# In theory, is there anywhere in the universe where velocity=0?

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Earth is traveling at a certain velocity. Earth orbits the Sun at velocity X. The sun is orbiting the center of our galaxy at velocity Y. The galaxy is orbiting (something?) at velocity Z. On and on…

In relation to zero, Earth has a velocity of X + Y + Z + (?).

Is it theoretically possible that there would be a point in space where nothing is moving and velocity is essentially 0?

If so, what would time look like at this point in space?

Yes.

The velocities you list (X, Y,… ) are all velocities with respect to some reference frame. But all reference frames are arbitrary, and you can always define a reference frame where the velocity of some object is exactly zero, as long as it's not accelerating.

For instance, Earth's velocity in the Sun's reference frame is X, but in its own reference frame, it's zero.

This is not just semantics; it is probably one of the most profound concepts in physics that there is no such thing as an "absolute frame of reference". Before Einstein, people thought that time and space are absolute, but Einstein taught us that everything is relative.

In cosmology, there is a special reference frame in which all matter on average is zero. The coordinates of this frame are called comoving coordinates, and in many cases it makes sense to regard this as the most natural reference frame. But it is important to remember that it is still just a choice, and that any other reference frame is equally legit, although a bad choice of reference may make certain calculations harder or impossible to solve. In comoving coordinates, the cosmic microwave background (CMB) is isotropic, i.e. it looks the same no matter which direction you look. But since Earth is traveling with a non-zero velocity in comoving coordinates (at an average of 369 km s$^{-1}$), the CMB is slightly blueshifted in the direction in which we're traveling, and slightly redshifted in the other direction.

What would time look like? Time runs slower, the faster you move. In any non-accelerating reference frame (an inertial system), time runs "as it should", but an observer in this frame who measures how time runs in a frame that has a non-zero velocity with respect to his/her frame, will see it run slower.

The question itself is wrong, actually.

There is no such thing as absolute velocity, which is what you're assuming in your question. Velocity is always relative to a frame of reference.

Your speed relative to your chair is zero, but it's not zero relative to the airplanes flying over your house.

When you say "a point in space where nothing is moving and velocity is essentially 0", you must add "relative to such-and-such frame of reference", otherwise your statement makes no sense.

By that token, any object in any point of space has zero speed relative to any frame of reference rigidly attached to it, and non-zero speed relative to other frames. You can't talk about speed unless you specify the frame against which it is measured.

Speed doesn't even exist by itself. It's always relative to a frame. It's not a property of an object or (even worse) a property of "a point in space". It's a relation between an object (the moving thing) and another object (the frame). "Points in space" don't have properties themselves, space is featureless.

Cars may seem like they have a speed as an intrinsic property, but that's just their speed relative to the ground. The car's speed relative to its driver is very different (and hopefully equal to zero). And the car's speed relative to a comet in the Solar System is yet again different.

Any further considerations, such as the flow of time, etc., are invalid as long as you're not asking the right question. Again, speed can only exist relative to something and, as such, it depends on the choice of the frame. And time depends on that whole causal chain.

## The Universe Has Probably Hosted Many Alien Civilizations: Study

Many other planets throughout the universe probably hosted intelligent life long before Earth did, a new study suggests.

The probability of a civilization developing on a potentially habitable alien planet would have to be less than one in 10 billion trillion — or one part in 10 to the 22nd power — for humanity to be the first technologically advanced species the cosmos has ever known, according to the study.

"To me, this implies that other intelligent, technology-producing species very likely have evolved before us," said lead author Adam Frank, a professor of physics and astronomy at the University of Rochester in New York. [13 Ways to Hunt Intelligent Alien Life]

In 1961, astronomer Frank Drake devised a formula to estimate the number of extraterrestrial civilizations that may exist today in the Milky Way.

Adam Frank and co-author Woodruff Sullivan of the University of Washington were interested in the odds that intelligent aliens have ever existed anywhere in the universe. So they tweaked the famous Drake equation, coming up with an "archaeological version" that doesn't take into account how long alien civilizations may last.

Frank and Sullivan also incorporated observations from NASA's Kepler space telescope and other instruments, which suggest that about 20 percent of all stars host planets in the life-friendly, "habitable zone," where liquid water could exist on a world's surface.

The researchers then calculated the probability that Earth was the universe's first-ever abode for intelligent life, after taking into account the number of stars in the observable universe (about 20 billion trillion, according to a recent estimate).

"From a fundamental perspective, the question is, 'Has it ever happened anywhere before?'" Frank said. "Our result is the first time anyone has been able to set any empirical answer for that question, and it is astonishingly likely that we are not the only time and place that an advanced civilization has evolved."

But this doesn't mean that there are lots of intelligent aliens out there, just waiting to be contacted, the researchers stressed.

"The universe is more than 13 billion years old," Sullivan said in the same statement. "That means that even if there have been 1,000 civilizations in our own galaxy, if they live only as long as we have been around — roughly 10,000 years — then all of them are likely already extinct. And others won&rsquot evolve until we are long gone. For us to have much chance of success in finding another 'contemporary' active technological civilization, on average they must last much longer than our present lifetime."

(The 10,000-year figure cited by Sullivan refers to humanity's development of agriculture and other "rudimentary" technologies mankind has been capable of sending radio waves and other electromagnetic signals out into the cosmos for just a century or so.)

The new study has been published in the journal Astrobiology you can read it for free here.

## Question Edgeless universe?

Galileo was active, somewhat, in the Church. He even did some papers such as one on Dante's work. But he wasn't regarded highly as a theologian, but as a great scientist. He was very well liked by the Jesuits, at first. They were located at College Romano (in Rome) and were the more official scientists of their day. Many were brilliant and some were famous mathematicians.

So, when Galileo made telescopes, and gave them to others, he was able to demonstrate a number of things. But the observation that falsified the 2000-year Artistotle model -- formalized by Ptolemy to create practical-use astrological tables, then infused into Catholocism by Thomas Aquinas (he saw the church might look foolish not to adopt such great and suddenly popular reasoning on many things from Aristotle) -- was the telescopic observation of Venus. The Earth-centered model does not allow both a crescent and gibbous phase, but yet it became clear after numerous observations, even with weak lenses and bad seeing conditions, that both those phases exist.

The Jesuits, many who still liked and respected Galileo, agreed that the Aristotle model was falsified -- not that their was any SM back then, but facts are facts after all. Galileo tried to argue that Copernicus was right and that the Sun is the center of the "world" (universe). But their literal religious views, and Council of Trent demands, and other dogma, got them to adopt the Earth-centered Tychonic model where the planets, except Earth, orbited the Sun. This allows Venus to have both phases. So they discounted the wonderful elegance and unification the Copernicus had in explaining things like retrogrades.

Galileo, who had great clout and world acclaim for his discoveries, inventions, and mathematical prowess, got approval to write a book that, he hoped, would turn others within his church to agree with Copernicus (a church canon) and other Church Cardinals who also supported him and Copernicus. The book he wrote argued that tides "proved" the Cop theory and he, unwisely, used the Pope's arguments in a belittling way, though I am sure he did not mean anything personal since the Pope was his friend. The Pope, with tons of more troubling issues, quickly lost patience with Galileo and that's when things started going downhill quickly. The trial ended with Galileo recanting and being stuck at home from then on. [He did write another remarkable book, nevetheless.]

So, if you didn't mind reading all that, the 300 years was the time the Church took to apologize for their mistake regarding their treatment of Galileo. I think it was in 1992. Their adoption, however, of the Tychonic model may have been in only several months. The Cop model was likely consiered more practical to use for planetray calculations so I suspect there was a gradual, but non-vocal, adoption of the Cop model long before 1992.

[Added: There is a term worth learning (teleology) if anyone finds interesting this period -- the birth of science. That time period held that all things in nature came with an intended purpose -- God's purpose. Science as it is today didn't exist as we know it then. Religion, being subjective, was infused with their science, so Galileo, when this was a problem for him, brilliantly argued that religion should be more flexible when discoveries (objective evidence) come along. Interpretations simply needed to be tweaked to make more sense whenever it became obvious a religious or philosophical view was in conflict with the evidence. He was probably the best at trying since he, IMO, was the first powerful person to properly combine today's SM elements including experiments, math, reasoning, etc. ]

#### Catastrophe

##### Approaching asteroid? Is this THE one?

You might like to have a look at this?

If The Universe Is 13.8 Billion Years Old, How Can We See 46 Billion Light Years Away?
Distances in the expanding Universe don’t work like you’d expect. Unless, that is, you learn to think like a cosmologist.

#### Catastrophe

##### Approaching asteroid? Is this THE one?

And here is the conclusion:
QUOTE
And so 92 billion light years might seem like a large number for a 13.8 billion year old Universe, but it’s the right number for the Universe we have today, full of matter, radiation, dark energy, and obeying the laws of General Relativity. The fact that space itself is expanding, and that new space is constantly getting created in between the bound galaxies, groups and clusters in the cosmos, is how the Universe got to be as big as it is to our eyes. Given what’s in it, what governs it and how it came to be, it couldn’t have turned out any other way.
QUOTE

#### Catastrophe

##### Approaching asteroid? Is this THE one?

Nope. There are many, many areas of misquotes and misunderstandings about those days. [The one that is most troubling is the claim that Bruno was burned at the stake for his views on astronomy.]

Galileo was active, somewhat, in the Church. He even did some papers such as one on Dante's work. But he wasn't regarded highly as a theologian, but as a great scientist. He was very well liked by the Jesuits, at first. They were located at College Romano (in Rome) and were the more official scientists of their day. Many were brilliant and some were famous mathematicians.

So, when Galileo made telescopes, and gave them to others, he was able to demonstrate a number of things. But the observation that falsified the 2000-year Artistotle model -- formalized by Ptolemy to create practical-use astrological tables, then infused into Catholocism by Thomas Aquinas (he saw the church might look foolish not to adopt such great and suddenly popular reasoning on many things from Aristotle) -- was the telescopic observation of Venus. The Earth-centered model does not allow both a crescent and gibbous phase, but yet it became clear after numerous observations, even with weak lenses and bad seeing conditions, that both those phases exist.

The Jesuits, many who still liked and respected Galileo, agreed that the Aristotle model was falsified -- not that their was any SM back then, but facts are facts after all. Galileo tried to argue that Copernicus was right and that the Sun is the center of the "world" (universe). But their literal religious views, and Council of Trent demands, and other dogma, got them to adopt the Earth-centered Tychonic model where the planets, except Earth, orbited the Sun. This allows Venus to have both phases. So they discounted the wonderful elegance and unification the Copernicus had in explaining things like retrogrades.

Galileo, who had great clout and world acclaim for his discoveries, inventions, and mathematical prowess, got approval to write a book that, he hoped, would turn others within his church to agree with Copernicus (a church canon) and other Church Cardinals who also supported him and Copernicus. The book he wrote argued that tides "proved" the Cop theory and he, unwisely, used the Pope's arguments in a belittling way, though I am sure he did not mean anything personal since the Pope was his friend. The Pope, with tons of more troubling issues, quickly lost patience with Galileo and that's when things started going downhill quickly. The trial ended with Galileo recanting and being stuck at home from then on. [He did write another remarkable book, nevetheless.]

So, if you didn't mind reading all that, the 300 years was the time the Church took to apologize for their mistake regarding their treatment of Galileo. I think it was in 1992. Their adoption, however, of the Tychonic model may have been in only several months. The Cop model was likely consiered more practical to use for planetray calculations so I suspect there was a gradual, but non-vocal, adoption of the Cop model long before 1992.

[Added: There is a term worth learning (teleology) if anyone finds interesting this period -- the birth of science. That time period held that all things in nature came with an intended purpose -- God's purpose. Science as it is today didn't exist as we know it then. Religion, being subjective, was infused with their science, so Galileo, when this was a problem for him, brilliantly argued that religion should be more flexible when discoveries (objective evidence) come along. Interpretations simply needed to be tweaked to make more sense whenever it became obvious a religious or philosophical view was in conflict with the evidence. He was probably the best at trying since he, IMO, was the first powerful person to properly combine today's SM elements including experiments, math, reasoning, etc. ]

## What does one mean when they say "Time is the fourth dimension", does it function like the other spatial dimensions?

I've often heard the idea that "Time is the fourth dimension" what does this mean? Could it be said that the entire (observable) Universe is traveling "forward" along the Fourth Dimensional axis? If it is a dimension why is it that everything seems to be "moving" in the same direction in this dimension?

Does everything "move" at the same speed?

Is there a force propelling all of existence "forward" through time?

No, because the time dimension acts differently in a geometric sense. It doesn't follow the pythagorean theorem.

For two spatial dimensions, the distance between two points is: d 2 = x 2 + y 2

But the 4d "length" between two events at different places and different times is:

Where c is the speed of light. The minus sign is the difference. This is known as hyperbolic geometry.

In a sense it's equivalent to an imaginary spacial dimension

Wait so. as t increases d goes to zero? Are we talking about two events' light cones intersecting?

It means you can specify the coordinates of an event with three spatial coordinates and a time coordinate. 5th Street and Third Avenue on street level at 5 PM is a coordinate in four dimensions.

Yeah-for example- why are you not sitting next to yourself on the couch? The x,y, and z of your location is the same as it was yesterday when you were on the couch, but you and previous you are in separate dimensions of time.

There's more to it than this. In Special Relativity, the Lorentz transformation (which tells us how to switch reference frames) couples time and space. This means roughly that two events that are close in space but far apart in time in one reference frame may be far apart in space but close in time in another reference frame. Therefore, to some extent, time is just space viewed from a different reference frame. In more precise language, a certain relativistic effect in one reference frame will occur because of length contraction, while the exact same effect in another reference frame occurs because of time dilation.

Is it just an abstraction then? Or is it an actual physical property similar to length-width-height?

So are all movies 3D then?

People have done an excellent job of answering the question in the title, so I'm hoping someone can answer the question in the text (which I find more interesting) to paraphrase :

By what mechanism does time move "forward", why are we progressing through time at all?

By what mechanism does time move "forward", why are we progressing through time at all?

Physics can't currently answer the "why" question here, but it can shed some light on the connection between time and the other dimensions.

Einstein's theories of special and general relativity treat the three dimensions of space and one time dimension as a single four-dimensional "space" called spacetime. Doing this turns out to have a very interesting consequence that directly relates to your question.

In classical mechanics in 3D space, we can represent an object's movement through space using a 3D velocity vector. This vector has a direction, pointing in the object's direction of motion through space, and a magnitude which represents its speed through space.

In spacetime, we can similarly represent an object's movement through spacetime using a 4D vector known as a four-velocity. This is a vector in 4D spacetime, and like any velocity vector, it has a direction which points somewhere/when in 4D spacetime, and a magnitude which represents the speed of the object through spacetime.

Yes! Here's where it gets interesting: the magnitude of an object's four-velocity, i.e. its speed through spacetime, is always equal to c, the speed of light. You are traveling at the speed of light through spacetime at this very moment.

Now, you may be sitting in a chair reading this, and wondering why you can't notice the fact that you're moving at the speed of light through spacetime. But it turns out, you can notice it, you just need to understand how to do that.

For a body (you) at rest in some reference frame, say sitting in a chair, the direction of your four-velocity lies entirely along the time coordinate. When "at rest", you're not moving through space at all, but you're moving through time at full speed, c.

You can observe this simply by watching the seconds ticking on a clock - if you're sitting still and the seconds are changing, you know you're moving at speed c through time. (Verifying that you're moving at c and not some other speed through time is beyond the scope of this comment - for now, just trust that Einstein knew what he was doing.)

This might all seem rather abstract, but it turns out to have real, testable consequences. In particular, when you're not at rest, and instead are moving through space, your speed through spacetime is still c, but now not all of it is along the time dimension - some of that constant speed has to go to your motion in the other dimensions. Which means, when you're moving in space, you're moving more slowly through time. Time will pass more slowly for you than it would have if you were at rest.

This, in a nutshell, is how the theory of special relativity works - at least, the aspect that relates to time dilation. You may already be aware that it's a well-verified theory - many scientific observations have confirmed that it's real, GPS satellites have to account for it, etc.

At our puny human speeds, we can't really notice how much the passage of time is affected by our motion through space, but we can measure it with precise enough instruments. For example, we can fly an atomic clock on a plane and observe that at the end of the trip, less time has passed for the moving clock than for a corresponding clock that remained at rest on the ground. This was first done by the Hafele-Keating experiment in 1971.

As a side note, it also turns out that gravity can be explained as curvature in 4D spacetime, making this view of spacetime as an integrated 4D continuum even more useful. This is the core of the theory of general relativity, the most accurate and well-verified theory of gravity.

Now, back to the original question - why are we progressing through time at all? As I said up front, we don't know why as such, but we do know that treating spacetime as an integrated 4D continuum produces a clear and natural relationship between space and time in 4D geometry, and tells us that everything is always moving at the same speed through spacetime. All we can change is which direction in spacetime we go.

In this model, time is still a "special" dimension, since no matter how much energy we apply to our motion through space, as objects with mass, we can never reach a speed of c through space, and thus the time component of our four-velocity is always non-zero - we're always traveling at some speed "forward" through time. But time is no longer something completely separate and apart from space, and the speed of travel of objects through time and space are directly related.

By what mechanism does time move "forward", why are we progressing through time at all?

As I understand it, that is actually an open problem in physics. If you look at physical equations they are generally invariant in the direction of time, that is to say, if we were to observe the universe "backwards" all of physics would hold true. Energy would still be conserved, so classical physical properties are not violated. This is counter-intuitive because it would be strange to observe water on a lawn leaping off the grass and forming a thin stream to enter a hose or a shattered vase collect its pieces and mend itself. Although energy is conserved, this does not happen. That behavior is prohibited by the second law of thermodynamics which defines Entropy, which may be thought of microscopically as a measure of disorder, and states that for any closed system, Entropy decreases monotonically with time. Because the second law seems to be the only defining feature of forward time, Entropy is sometimes referred to as the Arrow of Time.

Because we exist in a causal world. One event must be preceded by another. The first event is the cause and the second, the effect.

"Causality is not inherently implied in equations of motion, but postulated as an additional constraint that needs to be satisfied (i.e. a cause always precedes its effect)."

I'll leave relativity out of this for a minute and just answer from a purely Newtonian viewpoint.

A "dimension" is simply a degree of freedom an object has in which motion in that direction does not affect motion in any other direction. If you fire a bullet (in a vacuum so we neglect air friction) in the horizontal direction, its motion in that direction is not affected by whether or not gravity is acting on it. If there is a vertical gravitational field, the bullet will fall like any other object, and it will fall at the same rate as an object dropped with no motion in any other direction. But its fall will not affect its motion in the horizontal direction.

In this light, time is a dimension because it is totally orthogonal to the spatial directions. If you assume that time is ticking by independent of your motion (this is where the explanation becomes Newtonian), then you can have an object just sitting still, in which case it is "moving" solely in the time direction, or you can have an object moving, in which case it has another equation of motion in, say, the x direction, that is totally independent of its motion in the time direction (time is still ticking by at the same 'speed').

So horizontal velocity doesn't affect time of flight?

So let's start with space-like dimensions, since they're more intuitive. What are they? Well they're measurements one can make with a ruler, right? I can point in a direction and say the tv is 3 meters over there, and point in another direction and say the light is 2 meters up there, and so forth. It turns out that all of this pointing and measuring can be simplified to 3 measurements, a measurement up/down, a measurement left/right, and a measurement front/back. 3 rulers, mutually perpendicular will tell me the location of every object in the universe.

But, they only tell us the location relative to our starting position, where the zeros of the rulers are, our "origin" of the coordinate system. And they depend on our choice of what is up and down and left and right and forward and backward in that region. So what happens when we change our coordinate system, by say, rotating it?

Well we start with noting that the distance from the origin is d=sqrt(x 2 +y 2 +z 2 ). Now I rotate my axes in some way, and I get new measures of x and y and z. The rotation takes some of the measurement in x and turns it into some distance in y and z, and y into x and z, and z into x and y. But of course if I calculate d again I will get the exact same answer. Because my rotation didn't change the distance from the origin.

So now let's consider time. Time has some special properties, in that it has a(n apparent?) unidirectional ɿlow'. The exact nature of this is the matter of much philosophical debate over the ages, but let's talk physics not philosophy. Physically we notice one important fact about our universe. All observers measure light to travel at c regardless of their relative velocity. And more specifically as observers move relative to each other the way in which they measure distances and times change, they disagree on length along direction of travel, and they disagree with the rates their clocks tick, and they disagree about what events are simultaneous or not. But for this discussion what is most important is that they disagree in a very specific way.

Let's combine measurements on a clock and measurements on a ruler and discuss "events", things that happen at one place at one time. I can denote the location of an event by saying it's at (ct, x, y, z). You can, in all reality, think of c as just a "conversion factor" to get space and time in the same units. Many physicists just work in the convention that c=1 and choose how they measure distance and time appropriately eg, one could measure time in years, and distances in light-years.

Now let's look at what happens when we measure events between relative observers. Alice is stationary and Bob flies by at some fraction of the speed of light, usually called beta (beta=v/c), but I'll just use b (since I don't feel like looking up how to type a beta right now). We find that there's an important factor called the Lorentz gamma factor and it's defined to be (1-b 2 ) -1/2 and I'll just call it g for now. Let's further fix Alice's coordinate system such that Bob flies by in the +x direction. Well if we represent an event Alice measures as (ct, x, y, z) we will find Bob measures the event to be (g*ct-g*b*x, g*x-g*b*ct, y, z). This is called the Lorentz transformation. Essentially, you can look at it as a little bit of space acting like some time, and some time acting like some space. You see, the Lorentz transformation is much like a rotation, by taking some space measurement and turning it into a time measurement and time into space, just like a regular rotation turns some position in x into some position in y and z.

But if the Lorentz transformation is a rotation, what distance does it preserve? This is the really true beauty of relativity: s=sqrt(-(ct) 2 +x 2 +y 2 +z 2 ). You can choose your sign convention to be the other way if youɽ like, but what's important to see is the difference in sign between space and time. You can represent all the physics of special relativity by the above convention and saying that total space-time length is preserved between different observers.

So, what's a time-like dimension? It's the thing with the opposite sign from the space-like dimensions when you calculate length in space-time. We live in a universe with 3 space-like dimensions and 1 time-like dimension. To be more specific we call these "extended dimensions" as in they extend to very long distances. There are some ideas of "compact" dimensions within our extended ones such that the total distance you can move along any one of those dimensions is some very very tiny amount (10 -34 m or so).

Feel free to ask any followup questions

The "flow" of time is mostly a perception thing. Information only flows one way in time, and it can be said that this has to do with entropy, and the more mathematically probable (higher entropy) state being favored as time increases. Your memory is stored via chemical reactions, which behave under these laws of entropy, so you are experiencing this present moment, and you remember your past. But not everyone agrees on what is "the present" nor do they agree on what is "the past" or "the future."

## Contents

At temperatures near 0 K (−273.15 °C −459.67 °F), nearly all molecular motion ceases and ΔS = 0 for any adiabatic process, where S is the entropy. In such a circumstance, pure substances can (ideally) form perfect crystals as T → 0. Max Planck's strong form of the third law of thermodynamics states the entropy of a perfect crystal vanishes at absolute zero. The original Nernst heat theorem makes the weaker and less controversial claim that the entropy change for any isothermal process approaches zero as T → 0:

The implication is that the entropy of a perfect crystal approaches a constant value.

The Nernst postulate identifies the isotherm T = 0 as coincident with the adiabat S = 0, although other isotherms and adiabats are distinct. As no two adiabats intersect, no other adiabat can intersect the T = 0 isotherm. Consequently no adiabatic process initiated at nonzero temperature can lead to zero temperature. (≈ Callen, pp. 189–190)

A perfect crystal is one in which the internal lattice structure extends uninterrupted in all directions. The perfect order can be represented by translational symmetry along three (not usually orthogonal) axes. Every lattice element of the structure is in its proper place, whether it is a single atom or a molecular grouping. For substances that exist in two (or more) stable crystalline forms, such as diamond and graphite for carbon, there is a kind of chemical degeneracy. The question remains whether both can have zero entropy at T = 0 even though each is perfectly ordered.

Perfect crystals never occur in practice imperfections, and even entire amorphous material inclusions, can and do get "frozen in" at low temperatures, so transitions to more stable states do not occur.

Using the Debye model, the specific heat and entropy of a pure crystal are proportional to T 3 , while the enthalpy and chemical potential are proportional to T 4 . (Guggenheim, p. 111) These quantities drop toward their T = 0 limiting values and approach with zero slopes. For the specific heats at least, the limiting value itself is definitely zero, as borne out by experiments to below 10 K. Even the less detailed Einstein model shows this curious drop in specific heats. In fact, all specific heats vanish at absolute zero, not just those of crystals. Likewise for the coefficient of thermal expansion. Maxwell's relations show that various other quantities also vanish. These phenomena were unanticipated.

Since the relation between changes in Gibbs free energy (G), the enthalpy (H) and the entropy is

thus, as T decreases, ΔG and ΔH approach each other (so long as ΔS is bounded). Experimentally, it is found that all spontaneous processes (including chemical reactions) result in a decrease in G as they proceed toward equilibrium. If ΔS and/or T are small, the condition ΔG < 0 may imply that ΔH < 0, which would indicate an exothermic reaction. However, this is not required endothermic reactions can proceed spontaneously if the TΔS term is large enough.

Moreover, the slopes of the derivatives of ΔG and ΔH converge and are equal to zero at T = 0. This ensures that ΔG and ΔH are nearly the same over a considerable range of temperatures and justifies the approximate empirical Principle of Thomsen and Berthelot, which states that the equilibrium state to which a system proceeds is the one that evolves the greatest amount of heat, i.e., an actual process is the most exothermic one. (Callen, pp. 186–187)

One model that estimates the properties of an electron gas at absolute zero in metals is the Fermi gas. The electrons, being Fermions, must be in different quantum states, which leads the electrons to get very high typical velocities, even at absolute zero. The maximum energy that electrons can have at absolute zero is called the Fermi energy. The Fermi temperature is defined as this maximum energy divided by Boltzmann's constant, and is of the order of 80,000 K for typical electron densities found in metals. For temperatures significantly below the Fermi temperature, the electrons behave in almost the same way as at absolute zero. This explains the failure of the classical equipartition theorem for metals that eluded classical physicists in the late 19th century.

A Bose–Einstein condensate (BEC) is a state of matter of a dilute gas of weakly interacting bosons confined in an external potential and cooled to temperatures very near absolute zero. Under such conditions, a large fraction of the bosons occupy the lowest quantum state of the external potential, at which point quantum effects become apparent on a macroscopic scale. [5]

This state of matter was first predicted by Satyendra Nath Bose and Albert Einstein in 1924–25. Bose first sent a paper to Einstein on the quantum statistics of light quanta (now called photons). Einstein was impressed, translated the paper from English to German and submitted it for Bose to the Zeitschrift für Physik, which published it. Einstein then extended Bose's ideas to material particles (or matter) in two other papers. [6]

Seventy years later, in 1995, the first gaseous condensate was produced by Eric Cornell and Carl Wieman at the University of Colorado at Boulder NIST-JILA lab, using a gas of rubidium atoms cooled to 170 nanokelvins (nK) [7] ( 1.7 × 10 −7 K ). [8]

A record cold temperature of 450 ± 80 picokelvins (pK) ( 4.5 × 10 −10 K ) in a BEC of sodium atoms was achieved in 2003 by researchers at Massachusetts Institute of Technology (MIT). [9] The associated black-body (peak emittance) wavelength of 6,400 kilometers is roughly the radius of Earth.

Absolute, or thermodynamic, temperature is conventionally measured in kelvins (Celsius-scaled increments) and in the Rankine scale (Fahrenheit-scaled increments) with increasing rarity. Absolute temperature measurement is uniquely determined by a multiplicative constant which specifies the size of the degree, so the ratios of two absolute temperatures, T2/T1, are the same in all scales. The most transparent definition of this standard comes from the Maxwell–Boltzmann distribution. It can also be found in Fermi–Dirac statistics (for particles of half-integer spin) and Bose–Einstein statistics (for particles of integer spin). All of these define the relative numbers of particles in a system as decreasing exponential functions of energy (at the particle level) over kT, with k representing the Boltzmann constant and T representing the temperature observed at the macroscopic level. [1]

Temperatures that are expressed as negative numbers on the familiar Celsius or Fahrenheit scales are simply colder than the zero points of those scales. Certain systems can achieve truly negative temperatures that is, their thermodynamic temperature (expressed in kelvins) can be of a negative quantity. A system with a truly negative temperature is not colder than absolute zero. Rather, a system with a negative temperature is hotter than any system with a positive temperature, in the sense that if a negative-temperature system and a positive-temperature system come in contact, heat flows from the negative to the positive-temperature system. [10]

Most familiar systems cannot achieve negative temperatures because adding energy always increases their entropy. However, some systems have a maximum amount of energy that they can hold, and as they approach that maximum energy their entropy actually begins to decrease. Because temperature is defined by the relationship between energy and entropy, such a system's temperature becomes negative, even though energy is being added. [10] As a result, the Boltzmann factor for states of systems at negative temperature increases rather than decreases with increasing state energy. Therefore, no complete system, i.e. including the electromagnetic modes, can have negative temperatures, since there is no highest energy state, [ citation needed ] so that the sum of the probabilities of the states would diverge for negative temperatures. However, for quasi-equilibrium systems (e.g. spins out of equilibrium with the electromagnetic field) this argument does not apply, and negative effective temperatures are attainable.

On 3 January 2013, physicists announced that for the first time they had created a quantum gas made up of potassium atoms with a negative temperature in motional degrees of freedom. [11]

One of the first to discuss the possibility of an absolute minimal temperature was Robert Boyle. His 1665 New Experiments and Observations touching Cold, articulated the dispute known as the primum frigidum. [12] The concept was well known among naturalists of the time. Some contended an absolute minimum temperature occurred within earth (as one of the four classical elements), others within water, others air, and some more recently within nitre. But all of them seemed to agree that, "There is some body or other that is of its own nature supremely cold and by participation of which all other bodies obtain that quality." [13]

### Limit to the "degree of cold" Edit

The question whether there is a limit to the degree of coldness possible, and, if so, where the zero must be placed, was first addressed by the French physicist Guillaume Amontons in 1702, in connection with his improvements in the air thermometer. His instrument indicated temperatures by the height at which a certain mass of air sustained a column of mercury—the volume, or "spring" of the air varying with temperature. Amontons therefore argued that the zero of his thermometer would be that temperature at which the spring of the air was reduced to nothing. He used a scale that marked the boiling point of water at +73 and the melting point of ice at + 51 + 1 ⁄ 2 , so that the zero was equivalent to about −240 on the Celsius scale. [14] Amontons held that the absolute zero cannot be reached, so never attempted to compute it explicitly. [15] The value of −240 °C, or "431 divisions [in Fahrenheit's thermometer] below the cold of freezing water" [16] was published by George Martine in 1740.

This close approximation to the modern value of −273.15 °C [1] for the zero of the air thermometer was further improved upon in 1779 by Johann Heinrich Lambert, who observed that −270 °C (−454.00 °F 3.15 K) might be regarded as absolute cold. [17]

Values of this order for the absolute zero were not, however, universally accepted about this period. Pierre-Simon Laplace and Antoine Lavoisier, in their 1780 treatise on heat, arrived at values ranging from 1,500 to 3,000 below the freezing point of water, and thought that in any case it must be at least 600 below. John Dalton in his Chemical Philosophy gave ten calculations of this value, and finally adopted −3,000 °C as the natural zero of temperature.

### Lord Kelvin's work Edit

After James Prescott Joule had determined the mechanical equivalent of heat, Lord Kelvin approached the question from an entirely different point of view, and in 1848 devised a scale of absolute temperature that was independent of the properties of any particular substance and was based on Carnot's theory of the Motive Power of Heat and data published by Henri Victor Regnault. [18] It followed from the principles on which this scale was constructed that its zero was placed at −273 °C, at almost precisely the same point as the zero of the air thermometer. [14] This value was not immediately accepted values ranging from −271.1 °C (−455.98 °F) to −274.5 °C (−462.10 °F), derived from laboratory measurements and observations of astronomical refraction, remained in use in the early 20th century. [19]

### The race to absolute zero Edit

With a better theoretical understanding of absolute zero, scientists were eager to reach this temperature in the lab. [20] By 1845, Michael Faraday had managed to liquefy most gases then known to exist, and reached a new record for lowest temperatures by reaching −130 °C (−202 °F 143 K). Faraday believed that certain gases, such as oxygen, nitrogen, and hydrogen, were permanent gases and could not be liquefied. [21] Decades later, in 1873 Dutch theoretical scientist Johannes Diderik van der Waals demonstrated that these gases could be liquefied, but only under conditions of very high pressure and very low temperatures. In 1877, Louis Paul Cailletet in France and Raoul Pictet in Switzerland succeeded in producing the first droplets of liquid air −195 °C (−319.0 °F 78.1 K). This was followed in 1883 by the production of liquid oxygen −218 °C (−360.4 °F 55.1 K) by the Polish professors Zygmunt Wróblewski and Karol Olszewski.

Scottish chemist and physicist James Dewar and Dutch physicist Heike Kamerlingh Onnes took on the challenge to liquefy the remaining gases, hydrogen and helium. In 1898, after 20 years of effort, Dewar was first to liquefy hydrogen, reaching a new low-temperature record of −252 °C (−421.6 °F 21.1 K). However, Kamerlingh Onnes, his rival, was the first to liquefy helium, in 1908, using several precooling stages and the Hampson–Linde cycle. He lowered the temperature to the boiling point of helium −269 °C (−452.20 °F 4.15 K). By reducing the pressure of the liquid helium he achieved an even lower temperature, near 1.5 K. These were the coldest temperatures achieved on Earth at the time and his achievement earned him the Nobel Prize in 1913. [22] Kamerlingh Onnes would continue to study the properties of materials at temperatures near absolute zero, describing superconductivity and superfluids for the first time.

The average temperature of the universe today is approximately 2.73 kelvins (−270.42 °C −454.76 °F), based on measurements of cosmic microwave background radiation. [23] [24]

Absolute zero cannot be achieved, although it is possible to reach temperatures close to it through the use of cryocoolers, dilution refrigerators, and nuclear adiabatic demagnetization. The use of laser cooling has produced temperatures less than a billionth of a kelvin. [25] At very low temperatures in the vicinity of absolute zero, matter exhibits many unusual properties, including superconductivity, superfluidity, and Bose–Einstein condensation. To study such phenomena, scientists have worked to obtain even lower temperatures.

## In theory, is there anywhere in the universe where velocity=0? - Astronomy

In this epic documentary series, THE UNIVERSE takes you to the leading edge of our ever-expanding astronomical knowledge. A virtual collision of astronomy and history, these dense, enlightening episodes of unprecedented programming give unique insight - through recreations and animations - on the great "Eureka!" moments of celestial understanding and into the very latest discoveries. This insightful series gives serious, constructive consideration to the great human questions: Are we alone? Is Planet Earth as insignificant to the Cosmos as a drop of water? Is there anywhere else out there that that can support life? Or, is there truly no place like home?

In the second boundless season of THE UNIVERSE, THE HISTORY CHANNEL® takes you far beyond the comfort of our own solar system to discover the wonders of Deep Space. Venturing light-years from Earth, these programs guide you to the most fascinating phenomena and stunning events known to science.

Experience the Cosmos as no-one ever has - not peering at dots through a telescope or scanning pages of numbers - but firsthand. Strikingly realistic computer reconstructions give you a front-row seat at the hottest events in THE UNIVERSE, from colliding celestial bodies to collapsing suns, from distant, possibly viable planets to mysteries that defy explanation.
Source: History Channel

Part 01 - Alien Planets
Have planet hunters finally found proof of other Earthlike worlds? Astronomers have now discovered over two hundred alien worlds, beyond our solar system, that were unknown just a decade ago. Discover planets that rage with fiery hurricanes and bizarre planets covered by water so dense that it forms a kind of hot ice. Among these weird worlds, Earth actually seems like the oddball with the right conditions for life.

Part 02 - Cosmic Holes
Today, we know black holes exist, and now scientists are trying to confirm that other holes lurk in hyperspace. Our infinite cosmos could contain a variety of "holes" such as black, white, "mini" and wormholes. White holes are the reverse of black holes instead of matter being sucked into it, matter is ejected out. Wormholes are gateways in the fabric of space and time. They are included in Einstein's field equations as possibilities for their existence. Neither white holes nor wormholes have ever been found. Learn about new discoveries including, colliding binary black holes, intermediate black holes and manufacturing mini black holes.

Part 03 - Mysteries of the Moon
For thousands of years, mankind has found comfort in its presence. It's been a lantern for nighttime travelers, a timekeeper for farmers, and a location finder for sailors at sea. For some cultures, it's even been a god. It's the only cosmic body ever visited by human beings. From afar, the Moon's luminance has captivated us since the beginning of time. And a closer look at the beacon in the dark sky reveals an ever-present source of myth, intrigue, controversy and unsolved mysteries. The field of science may cast an empirical light on some things about the Universe, but lunar experts are the first to admit they don't have all the answers when it comes to our Moon. This episode explores the theories behind Lunar Transient Phenomena that have left scientists stumped for centuries takes to the Canadian waters to see how the Moon effects our planet through tides and dusts off some age-old myths and weighs arguments that without our Moon, humanity may not even exist.

Part 04 - The Milky Way
We used to think that Earth was at the center of the universe, but now we know we're not even at the center of our own galaxy. Countless wonders exist between where earth is situated and the massive black hole at the galactic center of our solar system. Within the Milky Way can be found the debris of old, dying stars fueling the birth of new stars and at the galactic center hypervelocity stars get catapulted clear beyond the Milky Way's outer rim at unimaginable speeds. Come along for a guided tour of 100,000 light-year-wide family of stars and stellar phenomena we call The Milky Way.

Part 05 - Alien Moons
Travel from the inner solar system to the Kuiper Belt and explore the moons surrounding the planets of the solar system. Many of these moons that were once unknown are now on the cutting edge of astronomical study. Some burst with volcanic fury another spews icy geysers and others offer the possibility of alien life. Are these strange worlds simply hostile environments unfit for humans or do other possibilities exist? Cutting-edge computer graphics are used to bring the universe down to earth and to imagine what kind of life forms might evolve in alien atmospheres.

Part 06 - Dark Matter / Dark Energy
Scientists have no idea what it is, but Dark Matter and Dark Energy make up 96% of the Universe. Dark Matter is everywhere. It passes through everything we know on earth at billions of particles every second, yet no one has ever gotten a direct detection of this mysterious dark substance. An even more bewildering force is Dark Energy, which is rapidly pushing apart our Universe. Discovered only ten years ago, scientists are struggling to comprehend its unusual characteristics and answer the ultimate question what is the fate of our Universe? Using cutting-edge computer graphics watch as the universe is brought down to earth.

Part 07 - Astrobiology
Scientists have no idea what it is, but Dark Matter and Dark Energy make up 96% of the Universe. Dark Matter is everywhere. It passes through everything we know on earth at billions of particles every second, yet no one has ever gotten a direct detection of this mysterious dark substance. An even more bewildering force is Dark Energy, which is rapidly pushing apart our Universe. Discovered only ten years ago, scientists are struggling to comprehend its unusual characteristics and answer the ultimate question what is the fate of our Universe? Using cutting-edge computer graphics watch as the universe is brought down to earth.

Part 08 - Space Travel
When man finally broke free of the Earth's gravitational pull the dream of traveling to other planets became a reality. Today scientists are proposing a bizarre array of technologies in the hope of traveling faster through space: from space craft sporting sails that catch laser beams, to propulsion engines powered by a bizarre entity known as anti-matter. Finally explore the science behind the seemingly fanciful notion of warp-drive and a theoretical particle that can travel faster than light.

Part 09 - Supernovas
A stellar explosion, the supernova is the sensational death of a star. It can shine as bright as 100 billion Suns and radiate as much energy as the Sun would emit over 10 billion years. Jets of high-energy light and matter are propelled into space and can cause massive Gamma Ray Bursts and emit intense X-ray radiation for thousands of years. Astronomers believe that this process creates the very building blocks of planets, people and plants. Meet the world's leading Supernova hunters, and take a look at recorded supernovas throughout history.

Part 10 - Constellations
A constellation is a group of stars that are connected together to form a figure or picture. These star pictures help organize the night sky and provide a useful tool for astronomers even today. Explore some of the 88 official constellations and learn about some of the highlights of each--like the star that's due to go supernova in the constellation Orion. Discover the 13th zodiac sign that no one talks about, and find out why Polaris, the North Star, will one day have to surrender its title.

Part 11 - Unexplained Mysteries
Delve into the myths, misconceptions, truths and amazing mysteries of our unique universe. Could life exist on Mars? Is time travel possible and does Einstein's theory of relativity support it? Is there a companion dark star to our sun and could it pose a threat to earth? Learn about the spark that lit the big bang. Take a journey from science fiction that predicted all these things, to the scientific reality of what they mean to us in the ever-changing universe.

Part 12 - Cosmic Collisions

It's been said that our universe is a cosmic shooting gallery. Gravity is moving everything around and things are bound to collide. Astronomers are attempting to understand how these collisions occur in the dark recesses of space. Learn about collisional families, which are clusters of comets and asteroids planetary collisions mass extinction impacts involving asteroids and comets stars collisions and galaxy cluster collisions. Cutting-edge computer graphics are used to bring this series down to earth as the heavens yield their greatest secrets.

Part 13 - Colonizing Space

Space colonization is no longer the fodder of science fiction, it is becoming a reality. Examine the efforts underway to establish a human colony on Mars, including how they plan to grow food, recycle wastewater and introduce greenhouse gases to revive the red planet and make it more habitable for humans. Cutting-edge computer graphics are used to bring the universe down to earth to show what life would be like on Mars, and to imagine what kind of life forms might evolve in alien atmospheres.

Part 14 - Nebulas
Take a tour through the "Art Gallery of the Galaxy" and view what are considered the "crown jewels" of the heavens. Nebulas are mysterious clouds of gas that aren't classified as stars, planets, moons or asteroids. Astronomers use the most sophisticated techniques to view them since they are practically invisible to the naked eye. Nothing less than stunning, nebulas glow, reflect or obscure the galaxy's light with amazing swirls of color. Nebulas mark the regions where the nothingness of space first coalesces, where stars are born and where stars die. Cutting-edge computer graphics are used to bring the universe down to earth.

Part 15 - Wildest Weather in the Cosmos
Imagine a tornado so powerful, it can form a planet, or winds sweeping across a planet but blowing at 6,000 miles per hour! How about rain. made of iron? Sounds like science fiction, but this type of weather is occurring daily in our solar system. Scientists are just beginning to unlock the secrets of these planets and their atmospheres. Can this research help scientists solve long unanswered questions that we have about Earth? As our own planet churns with the effects of global warming, it's natural to look into the heavens and wonder about the rest of the real estate.

Part 16 - Biggest Things in Space

We can't compare anything on earth to the biggest things known in space. The Lymann Alpha blob is a bubble like structure containing countless galaxies--perhaps the biggest object in the entire universe. Regions of radio-emitting gas called "radio lobes" could be even bigger. Then there are super galaxy clusters which are hundreds of galaxies merged together due to cosmic collisions. Discover which is the largest planet, star, star cluster, constellation, black hole, volcano, galaxy, explosions, moon, storm, impact crater and "void" in space.

Part 17 - Gravity
Gravity is the most powerful and exacting force in the universe. It is pervasive and penetrating. Gravity binds us together, its reach hangs stars in the sky and its grip crushes light. Gravity holds planets together, and leashes them to their suns. Without gravity, stars, comets, moons, nebulae, and even the Earth itself would not exist. Explore how science and humanity discovered, overcame and utilized gravity. Learn what it takes to propel objects into the heavens, to ride a wave or to ski down a slope. Take a front row seat as an astronaut subjects himself to the weightless wonders of the specially modified aircraft used to train astronauts known as the "Vomit Comet."

Part 18 - Cosmic Apocalypse
The Universe as we know it is condemned to death. Space, matter and even time will one day cease to exist and there's nothing we can do about it. Harsh realities are revealed about the future of our Universe it may collapse and burn or it might be gripped by a galactic ice age. Either of these scenarios might be a long way off. However, our Universe could suddenly be destroyed by a "random quantum fluctuation", a bubble of destruction that can obliterate the entire cosmos in the blink of an eye. No matter how it ends, life in our Universe is doomed.

Source: www.episodeworld.com

Review , from Amazon.com
With the DVD release (on five discs) of this, the complete second season of The Universe, the History Channel has now devoted a combined total of more than 25 hours, not including bonus material, to its documentary study of that combination of time, space, and matter that we call our universe. That&rsquos a lot. But then you consider the mind-boggling age and size of the universe itself: 13.7 billion years old, and big beyond our comprehension infinite, in fact, and expanding rapidly. By those measures, it&rsquos apparent that this fascinating series could probably air for longer than The Simpsons and Gunsmoke (the two longest running shows in TV history) put together and still not run out of things to talk about.

The 18 episodes from Season Two cover an appropriately wide range of topics, from "Cosmic Holes" to "Cosmic Collisions," from supernovas to gravity. There are episodes about the weather in space, the largest objects in space (hint: they&rsquore really, really big, like the so-called "cosmic web" of galaxies, which is a hundred million billion times bigger than Earth), and traveling to and colonizing space. The amount of information and data provided is enormous. Jargon abounds, including terms like "lunar transient phenomena," "pulsar planets," "hot Jupiters," "dark matter" and "dark energy," "collisional families," the "heavy bombardment period," and many, many more. And the numbers are mind-boggling: for instance, it&rsquos estimated that the impact of the asteroid that landed on the Yucatan Peninsula some 65 million years ago, wiping out the dinosaurs, was equal to that of dropping a Hiroshima-sized atomic bomb every second for 140 years! Still, some may find the episodes that involve informed speculation more interesting than those that deal in facts. We know that the Moon affects ocean tides, but does it also have an effect on human behavior? If the Big Bang was the beginning of the universe, what came before it? Instead of using rockets to go to space, can scientists actually build a "space elevator" that will reach from an orbiting satellite some 60 thousand miles down to Earth? All of this is delivered by way of very convincing computer-generated imagery and other effects, along with dozens of interviews with astronomers and other experts, photos, film footage, and so on. Best of all, while it can get a bit dense, technically speaking, by and large The Universe will be readily accessible to most viewers. --Sam Graham

Product Description

We once considered ourselves to be at the center of the universe now we know that we are just a small spec in a giant cosmos. This season, HISTORY® ventures outsides of our solar system in another epic exploration of the universe and its mysteries. With strikingly realistic computer re-creations, you ll feel like you ve traveled to the edge of the unknown: visit strange and unfamiliar worlds in Exoplanets, prepare for the worst in Cosmic Collisions, and uncover the secrets of our own galaxy, the Milky Way. And that s just the beginning. learn exactly what Dark Matter is and how it takes up 95% of the universe take a front-row seat for the ultimate light show with Supernovas and while most people have heard of black holes (which swallow all matter that they come in contact with), find out more about White Holes which actually create matter.

Customer Review

25 of 25 people found the following review helpful:
5.0 out of 5 stars Great series!, November 4, 2008
By Lulu (Doh, Qat)
I ordered this series with the thought 'what more can they do?' I seen it all in season one, it cannot top that. Was I wrong! It was even better. To realize that the universe is about 13.7 billion years old, and so vast, that it's totally beyond our comprehension and still expanding. A truly unimaginable thought, that. There are so many amazing episodes, one of which shows the largest objects in space. They are seriously big, like the so-called "cosmic web" of galaxies, which is a hundred million billion times bigger than Earth. Then there's the fascinating Lunar transient phenomena, the pulsar planets, the hot Jupiters, the weather in space, dark matter, dark energy, and much more. Really mind-boggling stuff, this!
For instance it's estimated that the impact of the asteroid that landed on the Yucatan Peninsula about 65 million years ago, wiping out the dinosaurs, this was equal to that of dropping a Hiroshima-sized atomic bomb every second for 140 years! And another mind-boggling thought, where did we really come from. hmmn. Still, I'd like to go to heaven eventually:)

This series had me riveted to my screen. The computer-generated imagery and other effects is so realistic. It makes one feel as if one is truly there experiencing this phenomenal aspects. And it's explained so simply that anyone can understand it.
My favourite episodes are: Alien Planets, Dark Matter, Astrobiology, Space Travel,Unexplained Mysteries & Colonizing Space. A truly awesome series! Enjoyed every bit of it.

## Does Zero Gravity Exist in Space?

We have all seen footage of astronauts floating freely in space, performing twists and turns that seem to defy gravity. As a result of these portrayals, many people believe that there is zero gravity in space. However, this statement could not be further from the truth. Gravity exists everywhere in the universe and is the most important force affecting all matter in space. In fact, without gravity, all matter would fly apart and everything would cease to exist.

Gravity is the attractive force between two objects at a fixed distance r. The strength of gravity is proportional to the mass of the two objects and inversely related the distance between them. A larger massed object has a greater gravitational force than a smaller massed object does which explains the difference between the gravitational field of the Earth and Moon. The force of gravity between two objects decreases rapidly at a rate of 1/r 2 . Thus, the gravitational force of two equal masses 1 meter apart is 100 times stronger than if the masses were 10 meters apart. Using the two parameters, mass and distance, we can understand how gravity operates in the universe and causes objects to appear as though they are experiencing zero gravity in space.

Earth’s gravitational pull is responsible for the moon’s orbit. Similarly, all planets, asteroids, and comets in our solar system orbit the sun due to this gravitational pull. The fact that celestial bodies millions of light years away orbit the sun debunks the myth of no gravity in space. The sun has a tremendous gravitational pull because it accounts for 99.86% of our solar system’s weight.

Why, then, are objects seemingly able to float freely in space despite the sun’s gravitational field? Remember, the force of gravity is dependent on the mass of two objects. The celestial bodies have enough mass to experience the gravitational pull of the sun. Objects with relatively little mass will experience less of the sun’s gravitational force than celestial bodies like Jupiter. In addition, small objects far from the sun experience a weaker gravitational force. Although gravity never reaches zero, it gets close.

The premise of Einstein’s theory of general relativity can be used to explain gravity in space. Imagine the universe as a two-dimensional sheet that represents the space-time fabric. If one were to place a ball with mass m on this sheet, it would create a depression that alters the space-time fabric. This distortion in gravity changes the progression of an object that passes through the depression. A ball with mass 2m will create a bigger depression and thus have a greater force of gravity acting upon it. The further an object is from the ball, the less it will experience the distortion or the ball’s gravitational field. Einstein’s theory postulates that any object with mass distorts space time, including humans. Although we barely dent the sheet, we create a small gravitational field around us. As long as there is matter in space, there is gravity.

The infamous astronomical phenomenon known as the black hole illustrates just how important gravity is in space. A black hole is a region in space so compact that light cannot escape it. Black holes are formed by dying stars that collapse under their own weight and form a core that is infinitely dense. In Einstein’s two-dimensional sheet analogy, a black hole is so compact that it creates a hole in the space time fabric instead of a dent. Any particle or wave, including light, is trapped by the enormous gravitational pull the black hole creates. The presence of black holes directly opposes the notion of zero gravity in space.

If all mass creates gravity in space, how did the notion of zero gravity originate? It has undoubtedly been fostered by the experiences of astronauts in space who seem weightless and are consequently described as experiencing zero gravity. This explanation cannot be true, especially so close to earth, where the gravitational field is strong and constantly pulling the spacecraft towards it. To understand the astronomer’s experiences, it is important to distinguish “weightlessness” from “zero-gravity.” Astronauts feel weightless because their shuttle is in a state of continuous free fall to the earth. However, the space shuttle never falls to the earth because it is traveling horizontally at about 18,000 km/hr, opposing the force of gravity. If the spacecraft was not moving quickly enough, it would fall prey to the effects of earth’s gravitational field and fall to the earth.

There is no such thing as zero gravity in space. Gravity is everywhere in the universe and manifests itself in black holes, celestial orbits, ocean tides, and even our own weight.

## The Everlasting Lightning Storm of Venezuela

There is a place in Venezuela that is home to a bizarre, raging storm that almost never ceases. It is a vast, throbbing beast of a storm that thrums with continual lightning and bellows forth with thunder an object of singular, electrifying intensity that seems more like an angry living thing than a mere weather phenomenon. In this place, for sometimes up to nearly 300 days a year, the lightning sizzles across the sky and licks at the earth below in a dazzling display of nature at its rawest and most furious. Here, in one, tiny, swampy corner of Venezuela the storm beast makes its lair, and produces the most breathtaking spectacle of a natural light show on earth.

This mesmerizing atmospheric phenomenon is known as Relámpago del Catatumbo, or Catatumbo lightning, and it only occurs in one very defined area of Venezuela, at the mouth of the Catatumbo River where it empties into Lake Maracaibo, in the state of Zulia. Here, the lightning almost never stops and it is startling in its intensity. For between 200 and 300 days a year, the storm produces an average of 28 strikes of lightning per minute for up to 10 hours at a time, sometimes unleashing up to 3,600 bolts of lightning per hour, or roughly one per second during particularly explosive displays, culminating in upwards of 40,000 lightning strikes a night. The National Weather Service calls 12 strikes per hour “excessive,” so yeah, it’s a lot of lightning. This immense amount of lightning is the single largest natural source of ozone in the world and is unique on this planet.

This lightning is not only produced in excessively large amounts, but is also remarkably powerful, with each bolt ranging from between 100,000 to 400,000 amps, far beyond the norm. This frighteningly potent lightning is so incredibly bright and constant that it is visible from up to 250 miles away, as a haunting, angry, flickering glow upon the horizon. This long distance visibility has led to the commonly held myth that the Catatumbo lightning is silent, since it can be seen from much farther away than its thunder can be heard. However, it does produce thunder, as all lightning does, in a a cacophony of unfettered, undiluted, raw noise. Nowhere else on Earth does lightning strike in such concentrations and with such relentless ferocity. The storm is also remarkably predictable, occurring in the exact same place every time, and starting practically on cue at around the same time, every time, just about an hour after dusk.

The Catatumbo lightning phenomenon has been well known for centuries. Natives of the region once referred to it as rib a-ba, or the “river of fire,” and revered it as a sign from the gods. Later, during the colonial period of the Caribbean, the highly visible light show was used as a means of navigation by sailors, who called it the “Lighthouse of Catatumbo” and the “Maracaibo Beacon.” The perpetual lightning storm also had a hand in changing history itself, as it was instrumental in the failure of at least two attempted surprise nighttime invasions of Venezuela. The lightning first betrayed the English Sir Francis Drake in 1595, lighting up the nocturnal invasion fleet and alerting nearby Spanish forces. In 1823, the Catatumbo lightning once again worked to thwart an invasion when it illuminated a Spanish fleet trying to sneak ashore under the cover of darkness during the Venezuelan War of Independence.

In addition to the sheer, staggering intensity of the storm is its continually shifting appearance. Depending on the level of humidity in the air on a particular night, the lightning bolts appear as different colors, and can even phase from one color to another in a single night. When air moisture is high, the minuscule airborne droplets of water act as a prism to scatter light and cause the lightning to become stunning explosions of brilliant red, pink, orange, and purple. When the air is dry, the lightning becomes crackling shocks of stark white in the absence of the prism effect.

This natural display of spectral beauty has its share of mysteries. For all of its majestic beauty and terrifying power, it has long been unclear as to what actually causes this ongoing storm to become so amped up and only in one small, well defined area. The most common explanation is that a combination of the unique topography and atmospheric conditions of the area, such as wind and heat, cause and feed the terrifying storm. The Lake Maracaibo Basin is surrounded on three sides by the Andes mountains, which form a sort of V that traps warm trade winds from the Caribbean. This hot air meets the cooler air descending from the mountains and the clash causes condensation. This condensation, plus the updrafts created by the additional moisture evaporating from the lake itself, creates the perfect recipe for the formation of thunderstorms.

It is also believed that the unique concentration and intensity of the lightning here can be attributed to the large reserves of methane that lie in the ground beneath the area. The Maracaibo basin sits atop one of the largest oil fields in the world, which produces vast quantities of methane gas. The theory is that this methane may seep into the atmosphere and increase conductivity, giving the thunderstorms and lightning an extra boost. Methane has sometimes been attributed to the myriad colors the lightning takes on as well. While undoubtedly there is a lot of methane to be found here, and it is now understood in particular concentrations under the epicenter of the storm activity, it is unclear how much of an influence, if any, it exerts on the storm. One popular theory in the 1960s was that uranium embedded in the bedrock of the basin might have some effect on the storm. Yet for all of the ideas put forth, at this point, it is not totally understood what causes the storm to rage so consistently and violently.

Another mystery to be found in the storm of Catatumdo is its tendency to suddenly stop for long periods. Although the lightning occasionally abates for short times, in 2010, after over a century of consistent, almost daily barrages of lightning, the Catatumbo storm suddenly and inexplicably ceased for over 6 weeks. With completely dark skies lasting from the end of January to the beginning of March, 2010, it was the longest calm in 104 years, so long in fact that scientists and people of the region feared that the rage of the storm had finally been spent. It was speculated that climate change and a drought caused by 2009’s powerful El Niño had conspired to snuff the lightning out forever. Then, as suddenly as it had gone quite, the storm once again roared to life to scorch the skies with its crackling lightning. No one is quite sure why the storm suddenly goes through quiet periods such as this, but they occur from time to time without warning. It is feared that ever increasing climate change could one day put an end to this unique and miraculous natural wonder forever.

For now, the Catatumbo lightning storm continues to light up the sky as it always has. It has become such a valued part of the country that Venezuela considers it a gift and a national treasure. The state where the storm occurs, Zulia, even features the lightning on its flag. The country is so proud of its never ending storm that it is actually pursuing plans to register the storm and its area as a UNESCO World Heritage Site, a classification that would be completely new for the organization as it typically only recognizes actual physical places. So far, these plans have not gone through, but the area does have the distinction of holding the Guinness World Record for most lightning strikes per square kilometer per year.

The Maracaibo Lake region and its Catatumbo lightning have become a big draw for tourists and scientists from all over the world, who come to study and experience the awe of this unrivaled natural spectacle. The country has made efforts to develop the area and turn the region into an eco-tourism zone to capitalize on the interest the storm has generated. This has proven to be difficult, as the region is infamous for harboring a myriad of drug dealers and armed guerilla groups, to the extent that the U.S. State Department advises against travel into the area. Nevertheless, looking at the raw power and beauty of this incredible natural phenomenon, one wonders if it may actually be worth it to make the journey.

This place is truly a unique, beautiful, and sometimes terrifying example of nature at its most furious. One can only hope that the continual transformation of our climate by humankind does not one day extinguish this unparalleled natural wonder forever.

## Is there anywhere big that wasn’t touched by the bombs

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Many places throughout the world probably avoided direct nuclear attack, but it's safe to say most major cities were hit. The true damage from the bombs came from the nuclear fallout and harsh winter that would follow the Great War, which probably killed just as many if not more people than the Great War itself.

Also it's important to remember the whole world was suffering from a resource shortage, which caused a lot of instability before the Great War started. Basically the world was fucked going into the Great War, the Great War just turbofucked it with nukes.

So Australia probably looked something like Mad Max before and after the Great War. But we have no idea what any other country looks like aside from a few offhand comments from a few characters.

c) to the resting distance d (where v' [the relative velocity] = 0).

However, there is work being done to quantize space-time in order to simplify physical problems with space-time at and smaller than the Planck scale. Quantum field theory breaks down at the Planck scale and this is the driving force and one of the final problems in coming up with a TOE (theory of everything). This is one of the instances when QM and Relativity clash.

**It's difficult (understatement) to probe into smaller and smaller information (Planck constant) about time/distance, mass/energy, etc. Just as its very difficult to probe light without mucking up your results (e.g. slit test).

At the current state of things, its impossible to tell if space-time is continuous or not at very small scales. Just as the mechanisms which cause randomness in QM are not explained, whether its turtles all the way down, whether there is an infinite universe or pink dragons just out of our line-of-sight, it's generally physics taboo to project your own opinions about "whats going on behind the scenes" without evidence of any kind.

I think that often times personal taste influences the understanding of physics. I've been guilty of it many times myself.

String theory (bleh) is taking a stab at quantum gravity, there is loop theory, and a whole muddled up mess of other things to confuse the crap out of everyone on the topic of 'how small is the smallest'.