Please explain the statement "the big bang happened everywhere at once"

[CaptDude]

Obviously, I can understand the literal meaning of the phrase "the big bang happened everywhere at once" But I have never read a satisfactory explanation that eloquently helped me understand this concept...

 

[Clayjay]

Space-time mathematically starts at a point. There is no space or time outside of the singularity at the start of the Big Bang. There was no time or space at that point. Then things change
and time and space are created at that point; they are linked together and define each other.

The Big Bang theory is an abstract construct created through math and geometry. What happened before the Big Bang in my view a distraction.

"Where is the center of expansion in the universe today" a student asked.

"All the points in the universe today are the center of expansion of the universe today because all points where the same point in the beginning" the professor replied.

Yes - the BB happened at a point in time not in space. Because; to me, the time differential logically preceded the space differential. So for the Big Bang model there is no space outside of space time.

Just remember 95% of the universe is covered with "Dark energy and matter" which is saying we know nothing about 95% of the observed universe. On a human scale we know a lot but on a cosmic scale we know little, but we have good leads.

 

[Bandersnatch]

Obviously, I can understand the literal meaning of the phrase "the big bang happened everywhere at once" But I have never read a satisfactory explanation that eloquently helped me understand this concept...

Imagine a volume of space. It may be either infinite in extent, or finite in a way that curves on itself, so that going straight in anyone direction makes you come back to where you started.

This space is filled with some sort of energy at high density and high temperature.

Pick any number of points in that space, and measure how far away they are spaced.

At some point in time, all the distanced you had measured begin to increase simultaineously. As a result, the temperature and density of all the energy filling the space drops. Where once there was only radiation, particles and antiparticles begin to pop up and manage to stay around longer and longer without annihilating. Finally it gets cold enough for the electrons and protons to combine which in turn allows light to move freely. That light is the CMBR. The distances keep on growing, and the stuff filling the space keeps on cooling and getting on average less dense (although local clumps of matter coalesce to eventually form galaxies).

That's pretty much the Big Bang theory. It states that the universe as we see it today expanded from an earlier hot and dense state. Nothing more. That's why a question of "where did it happen" is not really applicable. It happened in the universe, or it happened everywhere are the best answers one can come up with, but the real answer is that the question is just not very sensible - the only reason it keeps getting asked is that BB is often, and misleadingly, described as an explosion.

A natural follow-up question to ask is: but what happened earlier than that? Where did all that energy come from?
If the BB were a person, it'd say: "Don't know, don't care. Not my jurisdiction".

Another source of confusion is the distinction between the BB theory and BB singularity. The singularity is what you get if you try and extrapolate the expansion backwards in time until you reach infinite densities and infinite temperatures at t=0. This is still a statement about the totality of space, and the reason people tend to confate it with a point in space is probably due to the fact that they first tend to come in contact with the concept of singularity in the context of black holes, whose singularities are of the spatial variety. It's important to remember that singularity is just a region where mathematics breaks down. The function $y=1/x$ has got a singularity at x=0. It's just an indication that the function is undefined for a certain value of the variable.

 

[Chronos]

It's almost a matter of philosophy. The answer could be ... In the beginning, there was nothing - and it became everything: or, if you prefer; In the beginning, there was everything - and we still have most of it left.

 

[guywithdoubts]

That phrase is used to keep people aware that there is no center of the universe and that popular artistic depictions of the Big Bang (you know, the little bright light emanating things) are not correct. Like they explained before, if the universe is infinite or it's curved so that is finite but there are no boundaries (think of the balloon analogy), then all points started separating from each other, thus "it happened everywhere at once".

 

[phinds]

Space-time mathematically starts at a point.

I agree w/ your post but this opening statement promotes the mistaken belief that it started at a point in SPACE, which it did not (as you clearly point out later) since if it had, there would be a center to the universe and there would consequently be a preferred direction to the motion of the expansion. There is neither.

I realize I'm not telling you anything you don't already know, I'm just trying to help others who read this thread to not get caught up in that fallacy.

 

[PeterDonis]

Space-time mathematically starts at a point.

Actually, strictly speaking, it doesn't, because the point singularity is not actually part of spacetime--it can't be, because the values of physical invariants (like the curvature scalars) are infinite there. The point singularity is really a limit of spacelike hypersurfaces that have a smaller and smaller scale factor as you get closer and closer to the limit. Each such hypersurface represents an instant of cosmological time, so you are correct that the Big Bang is best viewed as a moment of time, not a place in space.

 

[Helios]

Supposing that the universe is infinite, then it is infinite for all times, there's just a change in a scale factor. What bugs me is how some universal happening can happen everywhere at once. We marvel at synchronized swimmers doing their act in sync. It seems that all of infinite space had to do something on cue to get things started, and this contradicts my intuition as to how this is possible.

 

[Torbjorn_L]

"the big bang happened everywhere at once"

That depends on what you mean by "big bang". As you can see below, you can redefine "big bang" in order to push it further and further back in time. [If you find it practicable. I sincerely don't know why people insist on doing this. It is my failing of imagination.]

Inflation removes the singularity that used to be attached to the start of the Hot Big Bang. As I understand it (not having studied general relativity) the removal is inherent:

"Hence general relativity cannot be used to show a singularity.

Penrose's theorem is more restricted, it only holds when matter obeys a stronger energy condition, called the dominant energy condition, which means that the energy is bigger than the pressure. All ordinary matter, with the exception of a vacuum expectation value of a scalar field, obeys this condition. During inflation, the universe violates the stronger dominant energy condition (but not the weak energy condition), and inflationary cosmologies avoid the initial big-bang singularity, rounding them out to a smooth beginning."

[ http://en.wikipedia.org/wiki/Penrose–Hawking_singularity_theorems ]

Maybe something that could be said to break down spacetime reasserts itself "later" if we manage to look further back in time. (I assume then as a result of exotic physics.)

In the meantime, it is much more generic to identify various definitions of big bang to a certain time, meaning the space volume experienced it "everywhere at once". (Whatever "it" means for you.)

 

[Torbjorn_L]

It seems that all of infinite space had to do something on cue to get things started, and this contradicts my intuition as to how this is possible.

So far something like "all of ... space had to do something on cue" (or contra-intuitively, "infinite") has not been a necessary description.

The scale factor can expand space faster than the universal speed limit of anything within space, and the inflationary mechanism that solves the horizon problem so it appears everything happened on cue involves having a finite volume described as the observable universe..

The same appearance goes for the Hot Big Bang events, the only difference is that they happen over a larger volume (the local universe) intersected by the observable universe.

 

[PeterDonis]

What bugs me is how some universal happening can happen everywhere at once.

The Big Bang is not a "happening" in this sense. In the simple model with an initial singularity (i.e., without inflation and the refinements that leads to, which Torbjorn_L described in his post), the Big Bang just refers to that initial singularity, which is a boundary of spacetime, not a "happening". In inflation models where there is no initial singularity, the Big Bang just refers to the fact that, when the inflation period ends, the universe is filled with matter and radiation in an extremely hot, dense state, and is expanding very fast. This is not a single "happening", it's just a global description of the state of the universe at that instant of cosmological time; the "happenings" are the individual bits of matter and radiation in each little volume of the universe.

 

[Helios]

Do cosmologist who believe in an original singularity believe that infinity can originate out of point? Or does a singularity necessarily imply a finite universe? Or conversely, would an infinite universe negate the singularity belief?

 

[phinds]

Do cosmologist who believe in an original singularity believe that infinity can originate out of point? Or does a singularity necessarily imply a finite universe? Or conversely, would an infinite universe negate the singularity belief?

"Singularity" just means "the place where our math model breaks down and we don't know WHAT the hell was/is going on". ("was" in the case of the BB, "is" in the case of a black hole). It iS NOT a point.

 

[PeterDonis]

Do cosmologist who believe in an original singularity believe that infinity can originate out of point?

No, they believe that the singularity is not part of spacetime. See post #7.

 

[CaptDude]

Guywithdoubts said: That phrase is used to keep people aware that there is no center of the universe and that popular artistic depictions of the Big Bang (you know, the little bright light emanating things) are not correct. Like they explained before, if the universe is infinite or it's curved so that is finite but there are no boundaries (think of the balloon analogy), then all points started separating from each other, thus "it happened everywhere at once".Thanks for all the replies. Very good information. However, I need to ask another question. Am I mistaken in saying I think the phrase "the big bang happened everywhere at once" could be rephrased as "inflation happened everywhere at once." Having asked that, even I don't think that is correct because, if I remember correctly, inflation began a micro-fraction of a second AFTER the big bang.
Yet a lot of you seem to be referrencing inflation in your answers.
Am I making it harder to understand than it is? Is my "eloquent" answer simply that space time started at a "point" (I know this is not correct but I don't know how to phrase it right) and then inflation expanded space/time to "everywhere at once"?
I also want to sk about the universe having to center. If the universe is infinite, that is understandable. But if the universe is finite, it is harder to understand. How can any finite geometric shape have no center?
P.S. I am very happy to have found a place to enrich my understanding of life, the universe, and everything. ;)

 

[phinds]

Thanks for all the replies. Very good information. However, I need to ask another question. Am I mistaken in saying I think the phrase "the big bang happened everywhere at once" could be rephrased as "inflation happened everywhere at once." Having asked that, even I don't think that is correct because, if I remember correctly, inflation began a micro-fraction of a second AFTER the big bang.
Yet a lot of you seem to be referrencing inflation in your answers.
Am I making it harder to understand than it is? Is my "eloquent" answer simply that space time started at a "point" (I know this is not correct but I don't know how to phrase it right) and then inflation expanded space/time to "everywhere at once"?
P.S. I am very happy to have found a place to enrich my understanding of life, the universe, and everything. ;)

You are getting confused because of the two radically different ways the term "big bang" is used. One way, the only way in my opinion that is meaningful or helpful, is the "Big Bang Theory" which is a very (but not completely well understood description of how the universe evolved starting at about one Planck Time after the "singularity" and saying NOTHING about anything before one Planck Time (other than "don't know WHAT was going on back then") and the other is just a reference to the singularity (more properly called the Big Bang Singularity) which is just a place where the math model breaks down and something we can't really say anything meaningful about (other than "don't know WHAT was going on back then")

Also, I would suggest that you refrain from saying that anything started out at a point and just say that it started out at a TIME and we don't know HOW it started out but we know a lot about what happened since then.

 

[CaptDude]

Do cosmologist who believe in an original singularity believe that infinity can originate out of point? Or does a singularity necessarily imply a finite universe? Or conversely, would an infinite universe negate the singularity belief?

I find this to be a very interesting question. Could somebody please give a thoughtful reply?

 

[Helios]

For an infinite universe, I don't believe that shrinking the scale factor will every result in a point. A point is finite. An infinite universe does not extrapolate back to a point. It never resembles a point at any stage, ever. A point-singularity is absurd.

But an infinite singularity ( sounds oxymoronic ) also is confounding. How can time start everywhere at once. It's as if we had an infinite number of marathon runners poised on an infinitely long starting line and God says "on your mark, get set go" and he fires a track pistol. Or how could inflation begin or end everywhere at once, as if a memo were distributed "inflation will begin in one second" and the whole infinite universe is going to get the word.

 

[PeterDonis]

For an infinite universe, I don't believe that shrinking the scale factor will every result in a point.

The point is not part of spacetime (see my previous posts), so it's not the result of "shrinking the scale factor" the way you appear to be thinking of it.

However, it is true that the limit of the scale factor as the singularity is approached is zero. This could be described (sloppily) as "shrinking to a point". But it's not a "shrinking" in any physical sense; it's just a mathematical statement about a limit.

How can time start everywhere at once.

Time doesn't have to "start". It's just a coordinate, a way of labeing events. Or, if you like, a way of slicing up spacetime into an infinite sequence of spacelike slices, each of which is labeled with a "time", and each of which represents "space at an instant of time". If the universe is spatially infinite, then each of those spacelike slices is infinite.

Or how could inflation begin or end everywhere at once

We actually don't know that it did, and inflationary models don't require it to. They only require that inflation began and ended homogeneously within our observable universe--which, since our observable universe was much, much, much, much smaller when inflation ended (smaller than an atomic nucleus, IIRC), does not present any problem.

 

[julcab12]

Actually that's how they describe and imagine singularity -- infinitesimal scale/density and the direction of the pure equation. Unless some dynamic is introduced. It can either bounce, tunnel or both depending on how we model reality. We really don't know. IMO It is more intuitive to think that our universe is in a state of transformations/transitions and identify each extent/event in a temporal fashion than weak origins and creation.

 

[Chronos]

Were we to observe the aftermath of a nuclear detonation, we would see an expanding cloud of hot, dense gas. Naively extrapolating backwards, it would appear to have originated from an infinitely hot, dense and dimensionless point. Obviously, it would be illogical to conclude a nuclear weapon was a dimensionless point [singularity]. While the BB was not in any sense a 'detonation', the math entices us towards a similarly illogical conclusion.

 

[CaptDude]

Am I mistaken in saying I think the phrase "the big bang happened everywhere at once" could be rephrased as "inflation happened everywhere at once." Having asked that, even I don't think that is correct because, if I remember correctly, inflation began a micro-fraction of a second AFTER the big bang.
Yet a lot of you seem to be referrencing inflation in your answers.
Am I making it harder to understand than it is? Is my "eloquent" answer simply that space time started at a "point" (I know this is not correct but I don't know how to phrase it right) and then inflation expanded space/time to "everywhere at once"?
I also want to sk about the universe having to center. If the universe is infinite, that is understandable. But if the universe is finite, it is harder to understand. How can any finite geometric shape have no center?

 

[Bandersnatch]

I also want to sk about the universe having to center. If the universe is infinite, that is understandable. But if the universe is finite, it is harder to understand. How can any finite geometric shape have no center?

Can you name the centre of the surface of a sphere?

 

[phinds]

Am I mistaken in saying I think the phrase "the big bang happened everywhere at once" could be rephrased as "inflation happened everywhere at once."

The statement is to emphasise that whatever the Big Bang Singularity was, it was not a single point in space as it is always portrayed on TV pop-sci programs.

I also want to sk about the universe having to center. If the universe is infinite, that is understandable. But if the universe is finite, it is harder to understand. How can any finite geometric shape have no center?

I suggest you read the article linked to in my signature.

 

[CaptDude]

Can you name the centre of the surface of a sphere?

THANK YOU! That is a very good answer to my second question on an intellectual and conceptional level.

 

[CaptDude]

y

The statement is to emphasise that whatever the Big Bang Singularity was, it was not a single point in space as it is always portrayed on TV pop-sci programs.
I suggest you read the article linked to in my signature.

I apologize if I am belaboring the point, but I really want to grasp the answers I am getting to my question; and since it seems this concept is one of the most misunderstood areas of cosmology, I will carry on with questions. I am getting there, but I have not arrived. Once again, I feel my following question is wrong - but I need to ask it anyway. So the statement "the big bang happened everywhere at once" is not to be taken literally but metaphorically?
P.S. Phinds, I did read your article before and after your previous post. Good stuff, thanks for the resource. I ask these questions after decades of self learning by reading about quantum entanglement, the duel slit experiment, Bose–Einstein condensate, the Copenhagen Interpretation of quantum systems, Heisenberg's uncertainty principle, Schrödinger's cats and kittens, gravity waves, and anything else I could find on quantum physics and cosmology. I state this to provide a list of subject for others to explore and to show I have some level of understanding and that my questions are to help me understand what I have not been able to learn from "traditional reading sources"

 

[DaveC426913]

So the statement "the big bang happened everywhere at once" is not to be taken literally but metaphorically?

Not sure why you'd think it's only metaphorical.

It may be counter-intuitive, but I think it's pretty literal.

The way to intuit it might be in recognizing that... "Everywhere" was a very small place, a long time ago.

 

[phinds]

y

I apologize if I am belaboring the point, but I really want to grasp the answers I am getting to my question; and since it seems this concept is one of the most misunderstood areas of cosmology, I will carry on with questions. I am getting there, but I have not arrived. Once again, I feel my following question is wrong - but I need to ask it anyway. So the statement "the big bang happened everywhere at once" is not to be taken literally but metaphorically?

It is quite appropriate to carry on when you still have questions. As Dave said, it IS literal, I was just emphasizing the aspect of its refuting the "singularity = point" point of view. We have no idea how big the early universe was. It might have been infinite or it might have been finite but unbounded (as bandersnatch pointed out).

P.S. Phinds, I did read your article before and after your previous post. Good stuff, thanks for the resource.

I had good input from a number of people here before I got to the final version.

I ask these questions after decades of self learning by reading about quantum entanglement, the duel slit experiment, Bose–Einstein condensate, the Copenhagen Interpretation of quantum systems, Heisenberg's uncertainty principle, Schrödinger's cats and kittens, gravity waves, and anything else I could find on quantum physics and cosmology. I state this to provide a list of subject for others to explore and to show I have some level of understanding and that my questions are to help me understand what I have not been able to learn from "traditional reading sources"

 

[CaptDude]

It is quite appropriate to carry on when you still have questions. As Dave said, it IS literal, I was just emphasizing the aspect of its refuting the "singularity = point" point of view. We have no idea how big the early universe was. It might have been infinite or it might have been finite but unbounded (as bandersnatch pointed out).

I had good input from a number of people here before I got to the final version.

Ok, just got back from taking my dog for a long walk while thinking about all the answers I have been getting to my question. (Thanks to everyone who took the time to respond) As I stated previously, I knew my question about it being a metaphor was wrong, but a lot of the answers I have been given were metaphors. I want to sum up my thinking on the responses I have gotten, and of course, ask more questions.
(1) The big bang did not happen in space, it happened in time.
Question: If space and time are heads and tails of the same coin (i.e. intimately related) how did the big bang happen in one but not the other?
(2) I have come to the conclusion that the big bang did not happen in space because - before the big bang (or at the moment of the big bang is probably the correct way to phrase it) there was no space for it to take place in. The big bang was the creation of “all places”
Question: see previous question.
(3) If #2 is correct, then space (all places) was (were) created at that moment so that we say “the big bang happened everywhere at once”

Not sure why you'd think it's only metaphorical.

It may be counter-intuitive, but I think it's pretty literal.

The way to intuit it might be in recognizing that... "Everywhere" was a very small place, a long time ago.

 

[phinds]

I think the problem with these concepts is that it didn't exactly happen IN space OR time, it CREATED space and time, at least according to current thinking (which could be wrong). This is an exceptionally weird concept.

 

[PeterDonis]

(1) The big bang did not happen in space, it happened in time.

Your follow-up question here shows that you are uncomfortable with this idea, which you should be. You are right that space and time go together.

If #2 is correct, then space (all places) was (were) created at that moment so that we say “the big bang happened everywhere at once”

This is correct as far as it goes; but you have left out one thing, which phinds mentioned: the Big Bang created time as well as space, because it created spacetime.

The only potential issue with this way of putting it is that the word "created" isn't really the right word, because it implies that spacetime was created from something else. A better way of putting it would be to say that the Big Bang is a boundary of spacetime; and since all spatial locations in spacetime are "next to" the boundary at the instant right after it, the Big Bang happened everywhere at once.

 

[phinds]

The only potential issue with this way of putting it is that the word "created" isn't really the right word, because it implies that spacetime was created from something else. A better way of putting it would be to say that the Big Bang is a boundary of spacetime; and since all spatial locations in spacetime are "next to" the boundary at the instant right after it, the Big Bang happened everywhere at once.

I agree this is a better way to express it. Thanks for that improvement on my statement.

 

[Doug Huffman]

The way I solved my conceptual issue was by asking myself to point towards the BB and then to point to where the BB is not.

That was a wonderful epiphany that removed all sorts of stumbling blocks to understanding BB, universes and Mega/multiverse.

 

[CaptDude]

Your follow-up question here shows that you are uncomfortable with this idea, which you should be. You are right that space and time go together.
This is correct as far as it goes; but you have left out one thing, which phinds mentioned: the Big Bang created time as well as space, because it created spacetime.

The only potential issue with this way of putting it is that the word "created" isn't really the right word, because it implies that spacetime was created from something else. A better way of putting it would be to say that the Big Bang is a boundary of spacetime; and since all spatial locations in spacetime are "next to" the boundary at the instant right after it, the Big Bang happened everywhere at once.

Thank you all so much for helping me come to what I consider "a satisfactory explanation that eloquently helps me understand this concept" (see my original question at the top of this thread) I didn’t want the answer to be in an analogy or a metaphor and I am quite happy with the resulting conclusion you all helped me come to.

 

[Chronos]

Semantic explanations are unavoidably analogous or metaphorical. Math is a much better tool, but, unfortunately, ours is too primitive to flesh out all the details.

 

[Ken G]

My take on the question "how can something happen everywhere at once" is that it is asking the question "how seriously should we take the cosmological principle." My answer to that is, "no more seriously than any other useful organizational principle in physics, like conservation laws, symmetry principles, etc." Organizational principles are how we make sense of a vastly complicated universe, but we generally run into trouble when we take them too seriously. At what point do we stop asking "how can we think about things to make better sense of it" and start asking "is this how things really are?" I don't think there's any reason to ever go from the first type to the second type. So I would reframe the question, "why do we find success in seeking a time coordinate that allows the universe to behave similarly at large scales at given times"? There could be a lot of answers to that, but if one adopts inflation, the answer is probably "because due to inflation, the spatial extent of the universe that we perceive is too small for us to notice any differences other than those that have developed later due to gravitational instabilities."

 

[mes314159]

It seems to me that a problem with the balloon analogy is that while all points on the surface of the balloon are equivalent, the "center of expansion" of the balloon is unique. But that center is not actually on the balloon of course, and is "outside" the balloon universe. Since this whole analogy is in three dimensions however, people may still think that there is a center of expansion within the universe. So a question, does the big bang have a "mathematical center" in a higher dimension of space-time (as in Sphereland), or is that still a poor analogy?

 

[David Carroll]

One thing I never understood was this: When I was in nuke school in the Navy (which is the extent of my knowledge of physics), the teachers told us that Temperature was the measure of the random molecular kinetic energy in a system. But I never understood how scientists define, in a mathematically rigorous way, how "random" is measured in this context.

When I imagine the "Big Bang" - and I'm probably imagining it in the wrong way - I imagine a large mass of particles expanding uniformly from a single point. But if they are expanding uniformly, how could the mass of these particles have a temperature? "Uniformly", by any definition that I am personally aware of, seems about as opposite from "random" as one could possibly get. Can someone enlighten me on this matter?

 

[russ_watters]

Temperature is a measure of average kinetic energy. The fact that the direction of motion or the distribution of energies is random or has random components is irrelevant to that.

...and I'm not sure what that has to do with the Big Bang...

 

[David Carroll]

Temperature is a measure of average kinetic energy. The fact that the direction of motion or the distribution of energies is random or has random components is irrelevant to that.

...and I'm not sure what that has to do with the Big Bang...

Okay. Thanks, russ_watters.

Well, I asked because physicists will come out and say that the universe had "x" temperature when the universe was "y" minutes old.

 

[DaveC426913]

It seems to me that a problem with the balloon analogy is that while all points on the surface of the balloon are equivalent, the "center of expansion" of the balloon is unique. But that center is not actually on the balloon of course, and is "outside" the balloon universe. Since this whole analogy is in three dimensions however, people may still think that there is a center of expansion within the universe.

Yup, all analogies fall short of the real thing.

So a question, does the big bang have a "mathematical center" in a higher dimension of space-time (as in Sphereland),...?

No, the curvature works in 3 dimensions without there having to be a centre in a 4th dimension.

 

[David Carroll]

Temperature is a measure of average kinetic energy. The fact that the direction of motion or the distribution of energies is random or has random components is irrelevant to that.

...and I'm not sure what that has to do with the Big Bang...

But then if a projectile crashes, do we not say that the kinetic energy in the projectile was partly converted to heat? And wouldn't that imply that, post-crash, the temperature of the system registers a higher temperature than it did pre-crash? But the average kinetic energy of the system pre-crash would simply be the kinetic energy derived from the projectile's motion plus its pre-crash temperature, wouldn't it. So where did the higher temperature come from, post-crash?

I don't mean to take it off-topic. But we ARE on the topic of the big bang happening everywhere at once. And this is precisely relevant to a question I have on the big bang happening everywhere at once.

 

[vela]

Temperature is a measure of average kinetic energy. The fact that the direction of motion or the distribution of energies is random or has random components is irrelevant to that.

I wouldn't say it's irrelevant. When a pitcher throws a baseball, the average kinetic energy of all the particles increases, but you wouldn't say the temperature of the baseball has increased.

 

[vela]

When I imagine the "Big Bang" - and I'm probably imagining it in the wrong way - I imagine a large mass of particles expanding uniformly from a single point.

This thread is precisely about how this is not the correct way to picture the Big Bang.

 

[David Carroll]

This thread is precisely about how this is not the correct way to picture the Big Bang.

Good to know. But, at the very least, no one can accuse me of being off-topic. ;)

 

[russ_watters]

I wouldn't say it's irrelevant. When a pitcher throws a baseball, the average kinetic energy of all the particles increases, but you wouldn't say the temperature of the baseball has increased.

You tried to break my explanation, but swung and missed [/baseball analogy]: I said "the fact that...the direction of motion is random...", so a baseball is not a correct example of my explanation.

 

[David Carroll]

Basically, my question boils down to this: in the first few seconds of the universe, was the expansion uniform? If so, how could the universe "have a temperature" in those first few seconds if temperature is a measure of the random kinetic energy of the particles (though russ_watters says that "random" has nothing to do with it)?

 

[russ_watters]

Basically, my question boils down to this: in the first few seconds of the universe, was the expansion uniform? If so, how could the universe "have a temperature" in those first few seconds if temperature is a measure of the random kinetic energy of the particles (though russ_watters says that "random" has nothing to do with it)?

The expansion was essentially uniform, but in addition to the uniform expansion, there was random motion.

Now we can bring the baseball in: if the baseball is moving in a straight line (or even: if it is sitting still on the ground!), can it have a temperature?

 

[dragoneyes001]

one question the term "infinite" is is tossed around as if its a guaranteed fact.

without any ability to prove the universe is in fact infinite doesn't that make most of the theories based on shaky ground?

 

[phinds]

one question the term "infinite" is is tossed around as if its a guaranteed fact.

without any ability to prove the universe is in fact infinite doesn't that make most of the theories based on shaky ground?

I'm not aware of any serious physicists who say that the universe is infinite. We don't know and that has no impact at all on any theories I'm aware of. What theories did you think would be impacted by discovering that the universe is finite but unbounded, as it may well be?