how does it be

[japan rocks/andromeda]

how does the universe never start even if it did what would be there before. it is all just an unsolvable brain teaser

[DanielC]

how does the universe never start even if it did what would be there before. it is all just an unsolvable brain teaser

 

The origin of the universe is not currently understood. To probe it, we need to start by developing a coherent theory of quantum gravity. Current research paths include String Theory, Loop Quantum Gravity and the "Exceptionally Simple Theory of Everything" (which, btw, is not simple in the sense that you understand it - the name is a mathematical pun).

[IM Egdall]

In addition to giving us a remarkably accurate model of gravity, Einstein's field equations provide an equally remarkable insight into the very existence of space and time. Per his gravitational field equations, if you remove all the matter and energy from the universe, you are left with no space, no time, no spacetime, no events in spacetime. You are left with nothing at all!

 

This has a deep meaning in the Big Bang theory. Per the theory, space and time in our universe began at the moment of the Big Bang. Thus before the Big Bang, before the existence of matter and energy, there was no space and no time. So under this construct, it makes no sense to ask what happened before the Big Bang; there was no "before" before the big bang!

 

 

 

Edited October 4, 2010 by I ME

[DanielC]

In addition to giving us a remarkably accurate model of gravity, Einstein's field equations provide an equally remarkable insight into the very existence of space and time. Per his gravitational field equations, if you remove all the matter and energy from the universe, you are left with no space, no time, no spacetime, no events in spacetime. You are left with nothing at all!

 

Can you justify this claim? I see nothing about the Einstein field equations that justify such claim. Start with:

 

G + lambda g = 8 pi T

 

If there is no matter or energy, then T = 0 and you get a universe of constant space-time curvature. There is nothing magical or special about this solution. This is in fact the simplest exercise when learning GR. There is nothing here that implies "no space, no time, no spacetime" like you suggested.

 

 

This has a deep meaning in the Big Bang theory. Per the theory, space and time in our universe began at the moment of the Big Bang.

 

Sorry to say, but I don't think you know what you are talking about. There is a sense in which you can say that space-time "began" at the Big Bang, but it has nothing to do with what you suggested. It has *nothing* to do with "remove matter and you get no universe".

 

The first thing you need to learn is that when we say that the universe is expanding, we mean that space itself is expanding / stretching. Run the clock backward and there was a time when the whole universe was the size of a tennis ball. This doesn't mean that there was a big empty universe and all matter was concentrated in a tiny space. No. The universe itself was that size. An ant crawling through that universe would have been able to walk on a "straight" line and come back to the point it started. Now continue running the clock backward and you find that at a time the entire universe was the size of an atom.

 

This is the picture that you should have in mind when you hear that space-time began at the Big Bang. The Big Bang is the expansion of the universe itself at the very beginning.

 

I hope some of what I've said made things clearer to you. If not, you could look for a GR textbook in your local library that can explain things a lot better than anything I can say in a forum post.

Edited October 4, 2010 by DanielC

[japan rocks/andromeda]

In addition to giving us a remarkably accurate model of gravity, Einstein's field equations provide an equally remarkable insight into the very existence of space and time. Per his gravitational field equations, if you remove all the matter and energy from the universe, you are left with no space, no time, no spacetime, no events in spacetime. You are left with nothing at all!

 

This has a deep meaning in the Big Bang theory. Per the theory, space and time in our universe began at the moment of the Big Bang. Thus before the Big Bang, before the existence of matter and energy, there was no space and no time. So under this construct, it makes no sense to ask what happened before the Big Bang; there was no "before" before the big bang!

 

 

 

i mean before the big bang there was nothing but how did nothing get there

[DanielC]

i mean before the big bang there was nothing but how did nothing get there

 

Don't listen to him. The truth is that we do not know what was happening in the early universe at around the Planck time (which is 10^(-44) sec). To understand the universe at this scale we need a theory of Quantum Gravity and we do not have one. So it is meaningless to make any claims about "before" the Big Bang or "what caused the Big Bang?". These are not questions that our current science can begin to address. One of the most intense research areas in physics today is quantum gravity, because we would really like to probe deeper and try to answer these kinds of questions.

[IM Egdall]

Can you justify this claim? I see nothing about the Einstein field equations that justify such claim. Start with:

 

G + lambda g = 8 pi T

 

If there is no matter or energy, then T = 0 and you get a universe of constant space-time curvature. There is nothing magical or special about this solution. This is in fact the simplest exercise when learning GR. There is nothing here that implies "no space, no time, no spacetime" like you suggested.

 

 

 

 

Sorry to say, but I don't think you know what you are talking about. There is a sense in which you can say that space-time "began" at the Big Bang, but it has nothing to do with what you suggested. It has *nothing* to do with "remove matter and you get no universe".

 

 

I realize that some new theory of quantum gravity may give us a new way of looking at "before" the big bang. But for now, we have to use the theory validated by empirical evidence; general relativity. I base "no matter/energy means no spacetime" on general relativity and the words of physicist John Stachel as well as Einstein. I believe I am correct. Please let me know what you think.

 

Spacetime does not claim existence on its own, but only as a structural quality of the (gravitational) field. - Albert Einstein

 

The Ricci Tensor and the Ricci scalar depend only on the Metric Tensor (in a complicated, non-linear way). So you can write the left-side of Einstein's field equations totally in terms of the Metric tensor. Thus spacetime curvature and how it changes is solely represented by the Metric Tensor. The Metric Tensor serves two functions; the ten g's represent both the gravitational field, and the underlying spacetime co-ordinates.[ii] Einstein realized that since the ten g's determine the underlying spacetime background, the so-called "metrical structure" of spacetime; then if there are no mass/energies, then there is no metric and there is no spacetime!

 

In Einstein construct, the gravitational field "must be determined before the points of spacetime (events) have any physical properties! In more formal language "the points of the spacetime manifold," writes Stachel, "only derive their physical individuation from the metric (gravitational) field,"[iv] This means you can't just start with a flat spacetime, then add the matter and energy and see how spacetime curves. There is no spacetime; no spacetime co-ordinates, no metric before you add the matter and energy.[v]

 

On the basis of the general theory of relativity . . . space as opposed to 'what fills space' . . . has no separate existence . . . If we imagine the gravitational field, i.e. the functions g_ab to be removed, there does not remain a (flat) space, but absolutely nothing . . . there is no such thing as an empty space, i.e. a space without a (gravitational) field. - Albert Einstein[viii]

(i) Einstein (1952). As cited in John Stachel, Einstein from 'B' to 'Z', p. 297.

[ii] Stachel, p. 294.

[iii] Stachel, p. 297-298.

[iv] Stachel, p. 304.

[v] ""In non-generally covariant theories, the structure of spacetime is given a priori." writes Stachel. "But in the generally covariant theory of general relativity, the gravitational field (i.e. the presence of mass/energy) produces the structure of spacetime." Thus spacetime events are defined with respect to a unique gravitational field. If there is no mass/energy, gravitational field; then there are no events! Stachel, p. 297

[vi] Stachel, p. 295-296.

[vii] As cited in Stachel, p. 297.

[viii] Einstein (1952). As cited in Stachel p. 297.<BR clear=all>

Edited October 5, 2010 by I ME

[MRlogic]

theres such a lot of theories of what was there before. some say its a never ending death and rebirth of universes one after each other. some say there are countless numbers of unverses with different laws of physics then ours

[DanielC]

I realize that some new theory of quantum gravity may give us a new way of looking at "before" the big bang.

 

Saying "a new way" is incorrect. Currently we have no way whatsoever. A theory of quantum gravity may or may not tell us something about the origin of the universe, and today we basically don't know anything. That's the most accurate way I can put it.

 

But for now, we have to use the theory validated by empirical evidence; general relativity.

 

There is an error here. We do not, and cannot, use GR to understand anything "before" the Big Bang, or, for that matter, a few Planck times after the Big Bang. This is a realm where quantum effects cannot be ignored (as they are in GR) and traditional GR is useless.

 

 

I base "no matter/energy means no spacetime" on general relativity and the words of physicist John Stachel as well as Einstein. I believe I am correct. Please let me know what you think.

 

I still think you are incorrect. I have studied GR, so I am speaking from personal knowledge. I believe that Stachel spoke poorly in some ways. Most, or nearly all of what he says is correct. But the way it is phrased, I understand how someone who is not familiar with the math behind GR might interpret things the way you did.

 

I believe that the key point Stachel is making, which is novel for most people, is that matter does not travel through a fixed space background (as most people imagine), but that space itself is a function of mass, and that even the very notion of distance and time (aka, the metric) are flexible concepts which only realize their meaning in the context of the matter and energy that is actually present in the universe.

 

In any case, it is perfectly possible to solve the Einstein field equations for a universe with no matter. These simply set the term T = 0 and they are known as "vacuum solutions". The simplest case is if the cosmological constant is also set to zero. In that case, the solution to the Einstein equations is just flat Minkowski space-time, which you may already be familiar with. Another interesting solution is the Kanser metric:

 

http://en.wikipedia.org/wiki/Kasner_metric

 

There is a Wikipedia article that talks about vacuum solutions: http://en.wikipedia.org/wiki/Vacuum_solution_(general_relativity). But I'm not sure how relevant it is for you because most of the solutions are not really about a universe that is devoid of matter, which is what you are interested in.

 

Personally I would like to see a solution for a universe with no matter, but a non-zero cosmological constant. I could try to do it myself, but I haven't done GR in a while and solving the Einstein field equations requires *a* *lot* of tedious work. I might give it a try next week when I'm less busy.

 

Hope this helps.

 

theres such a lot of theories of what was there before. some say its a never ending death and rebirth of universes one after each other. some say there are countless numbers of unverses with different laws of physics then ours

 

I don't like the use of the word "theory" in this context. A scientific theory is something that makes specific predictions that can be tested. The sort of hypothesis that you are talking about do not lead to any testable predictions.

[IM Egdall]

Saying "a new way" is incorrect. Currently we have no way whatsoever. A theory of quantum gravity may or may not tell us something about the origin of the universe, and today we basically don't know anything. That's the most accurate way I can put it.

 

 

I still think you are incorrect. I have studied GR, so I am speaking from personal knowledge. I believe that Stachel spoke poorly in some ways. Most, or nearly all of what he says is correct. But the way it is phrased, I understand how someone who is not familiar with the math behind GR might interpret things the way you did.

 

I believe that the key point Stachel is making, which is novel for most people, is that matter does not travel through a fixed space background (as most people imagine), but that space itself is a function of mass, and that even the very notion of distance and time (aka, the metric) are flexible concepts which only realize their meaning in the context of the matter and energy that is actually present in the universe.

 

In any case, it is perfectly possible to solve the Einstein field equations for a universe with no matter.

 

Thanks for your insights. I understand (or think I do) the dynamic nature of spacetime. However, I still have an issue. You say a solution to Einstein's equations are possible with a universe empty of matter and energy. I don't doubt you. But I am still wrestling with Einstein's words:

On the basis of the general theory of relativity . . . space as opposed to 'what fills space' . . . has no separate existence . . . If we imagine the gravitational field, i.e. the functions g_ab to be removed, there does not remain a (flat) space, but absolutely nothing . . . there is no such thing as an empty space, i.e. a space without a (gravitational) field.

If there is no matter/energy, then there is no gravitional field. And according to what Einstein is saying here, then there is no space. Your thoughts?

[DanielC]

Thanks for your insights. I understand (or think I do) the dynamic nature of spacetime. However, I still have an issue. You say a solution to Einstein's equations are possible with a universe empty of matter and energy. I don't doubt you. But I am still wrestling with Einstein's words:

On the basis of the general theory of relativity . . . space as opposed to 'what fills space' . . . has no separate existence . . . If we imagine the gravitational field, i.e. the functions g_ab to be removed, there does not remain a (flat) space, but absolutely nothing . . . there is no such thing as an empty space, i.e. a space without a (gravitational) field.

If there is no matter/energy, then there is no gravitional field. And according to what Einstein is saying here, then there is no space. Your thoughts?

 

If you read that quote carefully, Einstein did not say "matter", he said "gravitational field". Look closely:

 

"If we imagine the gravitational field, i.e. the functions g_ab to be removed, there does not remain a (flat) space, but absolutely nothing... there is no such thing as ... space without a (gravitational) field."

 

This is absolutely correct, but notice that he didn't say "matter", he said "gravity". In GR, what we call "gravity" is actually just the curvature of space-time. You cannot separate space-time from its curvature. I can make a very good analogy:

 

Think of a 2D surface: the surface of a sphere, a flat square, a cylinder, a saddle, etc. They all have a curvature, right? A sphere has positive curvature (lines that start parallel will converge), a saddle has negative curvature (lines that start parallel will diverge) and a flat square has a zero curvature (parallel lines remain parallel). Agreed? Now I imagine that I ask you to give me a 2D surface, but give it to me without any curvature... I want to add the curvature later. You'd say that that's not possible. Any 2D surface you can imagine has some curvature. It may be positive, negative, or zero, but it has something.

 

Your reply to me might be: "If we imagine the curvature ... to be removed, there does not remain a (flat) 2D surface, but absolutely nothing... there is no such thing as ... a 2D surface without a curvature."

 

The equations g_ab are the metric of space-time. The metric is the thing that tells you how space is curved. It is the function that lets you convert from your coordinate system to distance, and inherent in that formula is the curvature of your space. You are familiar with one metric: the metric of Eucledian 3D space. Imagine that I ask you to find the distance between two points (x0,y0,z0) and (x1,y1,z1). You would do this:

 

distance = sqrt( (x0-x1)^2 + (y0-y1)^2 + (z0-z1)^2 )

 

This is a metric. If you were using polar coordinates, the equation would look different. This equation describes the curvature of the space (in this case, it is flat). The equations g_ab are the formulas that describe distance, an hence curvature, in our universe.

 

Does this help?

 

Thanks for highlighting that quote. I didn't read it carefully enough the first time.

 

I can see how this can lead to confusion if you are not careful with language. In one context you might say that a flat square has no curvature, but what you really mean here is that it has a curvature of zero. Likewise, you might say that without matter there is no gravitational field, but in that case, what you mean is that you have a space-time curvature of zero. Then a week later, in a different context, you might say that every surface has to have a curvature, meaning that the curvature always has some value, even if that value is zero, just like you might say that you cannot have a universe without a gravitational field, because the universe always has some kind of curvature, even if it is zero. Then someone else reads these two quotes out of context and thinks that you are saying something that you didn't mean to say.

 

Does that help?

Edited October 7, 2010 by DanielC

[IM Egdall]

Thanks for your clear explanation. I see your point that flat curvature is still curvature. But, boy, the way Einstein states it can be misleading.

Edited October 8, 2010 by I ME

[DanielC]

Thanks for your clear explanation. I see your point that flat curvature is still curvature. But, boy, the way Einstein states it can be misleading.

 

I completely agree. I think that both Einstein and Stachel spoke poorly. Maybe Einstein was being asked a question orally and didn't have time to prepare a carefully thought-out answer, but Stachel was writing a book and he should have been more diligent in thinking about how the reader might interpret what he wrote and how he quoted.

[Airbrush]

DanielC, those are some excellent explanations, much of what I cannot follow, but thanks for your input. My background is art and accounting, with an interest in astronomy & cosmology.

 

Could you explain how the universe originated by a quantum fluctuation?

 

When do you expect the Large Hadron Collider will start making headlines? What do you think it may prove or disprove?

Edited October 10, 2010 by Airbrush

[DanielC]

DanielC, those are some excellent explanations, much of what I cannot follow, but thanks for your input. My background is art and accounting, with an interest in astronomy & cosmology.

 

Always happy to help.

 

Could you explain how the universe originated by a quantum fluctuation?

 

The correct, but boring answer is that I cannot. And anyone who says they can is probably lying or delusional. We do not understand how the universe originated. Anyone who says that it was by a quantum fluctuation is just putting words together because quantum mechanics and general relativity are both useless in the realm of the origin of the universe. The first thing we need before we can answer your question is a quantum theory of gravity, and we do not have that. There are some research projects trying to do that. One is String Theory, and another is Quantum Loop Gravity. But both projects have a lot of issues yet to resolve, and neither one has made a single prediction that we've tested.

 

When do you expect the Large Hadron Collider will start making headlines? What do you think it may prove or disprove?

 

I have no idea I know that's not what you want to hear, but on the other hand, this is why it's interesting. This is the process of discovery. You don't know what you are going to find out. But the #1 thing they hope to answer is whether the Higgs boson actually exists. It is predicted by quantum mechanics. If it doesn't exist, physicists will spend the next few years figuring out how to revise the theory of quantum mechanics.

 

I am not a particle physicists (my background is astrophysics) so I cannot really answer questions about the LHC. If I tried to answer, I'd basically just be copying from Wikipedia.