'A Universe From Nothing' by Lawrence Krauss, AAI 2009

[shoejunk]

Here's my amateur's take on the implications of a flat universe, having just watched Krauss' lecture and read these comments and done some of my own thinking. Please, let me know whether I'm making sense. In a flat universe, it's possible for there to be infinite mass and infinite space if the universe is expanding, because due to relativity, all the mass that is far enough away would be moving away from us faster than the speed of light and all of that mass would not be observable or have any affect on us in any way. It would be as if that mass doesn't exist for us. That leaves only a finite amount of mass that is not moving away from us faster than the speed of light, which is our observable universe, which is finite in both mass and spatial extent. So it's possible that the 'actual' universe is infinite in space and mass while our observable universe is finite in both ways.

Another thing I was thinking about is Krauss' picture of the future of the universe, when galaxies get so far apart that all galaxies are moving away from each other faster than the speed of light, and so as far as any observer could then tell, only the galaxy that is around the observer exists. Now consider the empty space between the galaxies. In that space, if all galaxies are moving away from the empty space faster than the speed of light, it would be as if there was absolutely nothing in the universe at all from the 'point of view' of that empty space. Now, isn't that the same situation that we were at at the beginning of the universe? So if the conditions are the same, shouldn't the outcome be the same? Shouldn't we expect quantum fluctuations to create universes from nothing? So what we end up with as a picture of our universe is an ever expanding universe in which matter keeps spreading out more and more, but in which more galaxies keep popping up within the empty spaces, albeit perhaps only when they are so far away that we can't notice them.

 

[Chalnoth]

Here's my amateur's take on the implications of a flat universe, having just watched Krauss' lecture and read these comments and done some of my own thinking. Please, let me know whether I'm making sense. In a flat universe, it's possible for there to be infinite mass and infinite space if the universe is expanding, because due to relativity, all the mass that is far enough away would be moving away from us faster than the speed of light and all of that mass would not be observable or have any affect on us in any way. It would be as if that mass doesn't exist for us.

Well, you actually get the same answer in Newtonian gravity in this case. It's due to the 1/r^2 falloff of gravity: stuff further away contributes less to the force, so that if you add up all the mass extending to infinity, the result is a finite effect.

Unfortunately, the speed of light limitation isn't so simple in General Relativity: most of the galaxies we see today have always been moving away faster than the speed of light, by the most obvious definition of speed (speeds of distant objects are actually arbitrary: there is no one choice of how to define it).

Another thing I was thinking about is Krauss' picture of the future of the universe, when galaxies get so far apart that all galaxies are moving away from each other faster than the speed of light, and so as far as any observer could then tell, only the galaxy that is around the observer exists. Now consider the empty space between the galaxies. In that space, if all galaxies are moving away from the empty space faster than the speed of light, it would be as if there was absolutely nothing in the universe at all from the 'point of view' of that empty space. Now, isn't that the same situation that we were at at the beginning of the universe? So if the conditions are the same, shouldn't the outcome be the same? Shouldn't we expect quantum fluctuations to create universes from nothing? So what we end up with as a picture of our universe is an ever expanding universe in which matter keeps spreading out more and more, but in which more galaxies keep popping up within the empty spaces, albeit perhaps only when they are so far away that we can't notice them.

Well, this view of galaxies popping out of the expanding space was actually championed a while ago as an alternative to the big bang theory, termed the steady state universe. The observation of the CMB, though, basically cemented that it's the big bang, not the steady state.

If there are "other universes" being produced out of vacuum fluctuations within our own universe, those universes would appear to us as microscopic black holes that fluctuate out of the vacuum, then rapidly decay again via Hawking radiation. They might extend in their own space-time off into infinity, but are only connected to us via a tiny blip that looks like a microscopic black hole. Forever after, they are disconnected and cannot interact with our universe in any way.

 

[heusdens]

I started this https://www.physicsforums.com/showthread.php?t=313501" a while ago talking about Stephen Hawking's "No Boundary Condition".

I think that I finally got a handle on it, but now Lawrence Krauss has discussed http://www.youtube.com/watch?v=7ImvlS8PLIo" why he thinks that the universe is not closed, but flat, and he says by implication, 'infinite in spatial extent'.
(he also claims to have empirical evidence of the flatness of space-time on the largest scales)

I don't understand how he can reconcile this with the big bang (which he also seems to accept).
If the universe is infinite in spatial extent, at what point did it become infinite, because when the universe was 1 second old, it was not infinitely large (I think that this is the scientifically accepted view).
He is obviously a widely respected physicist, and I am not a physicist, so I expect that I just don't understand what he is saying.

Could anyone explain it to me, or can it not be expressed in natural language?

Thanks,
Schlofster

In the metaphore of the universe being a flat sheet of rubber (the 2D analpgue of the 3D universe) that expands uniformly in all directions, it is true that (in the mathematical sense, not in the physical sense) all space we can observe now can be brought back to a single 0D spot, but that does not claim to say that all of space was just that single 0D dot.

It seems that too many people make this same implication, which is just an assumption, but doesn't need to be right. It would (IMHO) make more sense to assume that space near the Big bang was already infinite, and thus is still infinite.

This certainly makes sense in the context of the inflationary scenario, in which in other parts of the universe, inflation keeps gong on, creating ever more expanding universe bubbles.

 

[Nihar Shah]

Universe can be flat or not

But there are not only one universe , there are total 14 universes.

Out of 14 universes some universes can be flat and some can't

I think universe cannot be defined as it is flat or not, Actually it is out of the boundry of the word " flat "

 

[mikeyj4]

I still do not see enough evidence to prove any of these theories to be, or even close to being scientific law. Essentially, the idea is that all matter came from nothing, which then leads to the idea that life evolved from death. All of these concepts have not been proven by science and are at this point a belief. So these systems of beliefs, you could say is a religion. But, examining all of the evidence, does it not seem as if all of this creation was most likely caused or willed into existence by an outside consciousness. And obviously that consciousness would then be far more superior to ours if that be the case. The question I pose is why do we seek answers to all of these questions? Is it just out of curiosity? And what does this have to do with what we are doing or need to do here on Earth? Are we simply trying to find outside solutions to our problems here, rather than looking at ourselves and being humble and honest? Just some thoughts that I've been pondering.

 

[Chalnoth]

I still do not see enough evidence to prove any of these theories to be, or even close to being scientific law. Essentially, the idea is that all matter came from nothing, which then leads to the idea that life evolved from death.

These statements of yours are beyond ridiculous.

First, the birth of the universe has nothing whatsoever to do with the beginnings of life on Earth. The two are entirely different concepts, studied in entirely different branches of science. They have basically nothing to do with one another, and almost no information is or needs to be shared between those fields.

All of these concepts have not been proven by science and are at this point a belief.

You haven't been paying any attention whatsoever to the discussion, and have simply imposed your own blinkered views upon it. This isn't at all how science is done.

In this particular case, if you actually talk to scientists, they will say, "We don't know exactly, because the evidence is so far insufficient, but here's how it could have happened..."

Nowhere in there is a statement of belief. It's a statement of possibility. It's a statement that demands investigation. It relies upon current, tested knowledge, and speculates what may lie beyond.

And the fact of the matter is that current, tested knowledge suggests that it is very much possible for a universe to come from nothing, despite your dogmatic, religious insistence that it can't. "I don't believe it!" is not an argument. It's a statement of blind, evidence-free belief. Which you seem to not be so proud of.

So these systems of beliefs, you could say is a religion. But, examining all of the evidence, does it not seem as if all of this creation was most likely caused or willed into existence by an outside consciousness.

No. Not even remotely. There is nothing whatsoever in any piece of science that even hints at the possibility. Science has, instead, been pointing in entirely the opposite direction, continually upsetting our notions that the universe has some sort of direction or purpose. The overwhelming conclusion of science is that there is no direction or purpose to the universe, that the only direction or purpose that exist are the direction and purpose that we and other intelligent, evolved beings make for ourselves.

 

[revo74]

From my understanding we have indirect evidence of virtual particles. No one is debating whether they exist or not. What is speculative however is this notion that virtual particles could become Universes.

Assuming that Krauss is correct that our Universe was a virtual particle with the right conditions that underwent expansion and became a Universe, there is something I am confused about, which I'm hoping someone can address.

Krauss says that empty space or a vacuum in space at extremely small scales is not truly empty or "nothing". Instead there lies a brewing sea of energy where virtual particles pop in and out of existence in a fraction of a second. This suggests that this sea of energy is a feature of our Universe. It is not a separate entity. Now, it is my understanding that Krauss is claiming that our Universe spawned from this sea of energy, which suggests to me that one independent entity (our Universe) came from a separate entity (sea of energy). So does this mean that there are two entities? One which is a feature of our Universe and the other a realm of existence outside of our Universe where it came from?

In other words, how does the Universe "come from" a place that is part of it?

 

[Chalnoth]

In other words, how does the Universe "come from" a place that is part of it?

Well, this picture is one where our region of space-time was birthed from some other region of space-time, and that if you want to take the collection of all regions of space-time, that collection is eternal.

But in a very real sense, if you look into the far future of our own region of space-time, the most likely future is one where essentially nothing exists. All of the radiation will be redshifted away. All of the matter will have fallen into black holes or decayed, and all of those black holes will have then decayed. From this vast emptiness, however, new universes may be born.

That is the current best picture of a "universe from nothing". Yes, it isn't literally nothing. But nobody knows how to describe that mathematically anyway.

 

[revo74]

Well, this picture is one where our region of space-time was birthed from some other region of space-time, and that if you want to take the collection of all regions of space-time, that collection is eternal.

But in a very real sense, if you look into the far future of our own region of space-time, the most likely future is one where essentially nothing exists. All of the radiation will be redshifted away. All of the matter will have fallen into black holes or decayed, and all of those black holes will have then decayed. From this vast emptiness, however, new universes may be born.

That is the current best picture of a "universe from nothing". Yes, it isn't literally nothing. But nobody knows how to describe that mathematically anyway.

Thanks for the response.

I have another question then.

Is this "region" of space-time which our Universe spawned from some special place that gives birth to universes. A universe generator if you will or is it is another universe like ours? In addition, what would happen if a virtual particle in our own universe had the right conditions to become a new universe? Would it separate from our space-time continuum or expand within it? If the later I would have to image this would cause extreme catastrophe.

 

[Chalnoth]

Thanks for the response.

I have another question then.

Is this "region" of space-time which our Universe spawned from some special place that gives birth to universes.

No, not at all! It's just what we expect to happen everywhere from time to time.

In addition, what would happen if a virtual particle in our own universe had the right conditions to become a new universe? Would it separate from our space-time continuum or expand within it? If the later I would have to image this would cause extreme catastrophe.

Well, from our perspective, it looks like a microscopic black hole that almost instantly evaporates. But inside this microscopic black hole, the space-time becomes sort of twisted enough that a piece of it pinches off and expands on its own, independent of our universe.

 

[revo74]

No, not at all! It's just what we expect to happen everywhere from time to time.

So universes give rise to other universes. Do the laws of physics remain the same. Are these new universes essentially clones?

Well, from our perspective, it looks like a microscopic black hole that almost instantly evaporates. But inside this microscopic black hole, the space-time becomes sort of twisted enough that a piece of it pinches off and expands on its own, independent of our universe.

Would this be common sense speculation? After all the entire idea that our Universe is a special virtual particle is highly speculative to begin with.

What evidence or reasoning is there that supports this concept?

 

[Drakkith]

What evidence or reasoning is there that supports this concept?

None other than some math as far as I know. Similar to other different multiverse ideas.

 

[Chalnoth]

So universes give rise to other universes. Do the laws of physics remain the same. Are these new universes essentially clones?

Right now we don't have enough evidence to say for sure, but the general expectation is that the laws can be quite different every time.

Would this be common sense speculation? After all the entire idea that our Universe is a special virtual particle is highly speculative to begin with.

What evidence or reasoning is there that supports this concept?

In general this sort of idea is very much at the frontier of knowledge. The models we have today seem to suggest that this kind of thing is possible, but it's very difficult to say what actually happens in this regime. So for the most part, this should be filed under, "Possible idea. Needs work."

 

[Flatland]

The universe can be flat and still be finite and unbounded.