Did the Universe appear from an infinitely dense, infinitely small point?

[Aethelwulf]

And I really don't want to hear the ''this is not what mainstream says'' rubbish. I have read plenty texts on this subject and I can assure you, this is what maintream says.

Hawking has said this, Penrose has said this... leading Cosmologists have said this. This is in fact what is still being taught in universities. The reason why is because in the very initial state of the universe, there was no size we can speak about. Also, quantum mechanics can go to this state easily, but relativity would permit a singularity in this region. Some have considered this a break down on the theory.

And I am not talking about after the Planck Epoch, I would hope that part is clear enough.

[Aethelwulf]

Here is a discussion at physicsforums which I have been apart of for a while. The contributors quite clearly note that the current model we deal with is in fact one which arose from an infinitely dense, infinitely small point http://www.physicsforums.com/showthread.php?t=472481

[Shaula]

This is in fact what is still being taught in universities.

Statement is falsified by the fact that this was not what I was taught in university where I studied astronomy.

Anyone commenting on pre-Planck time physics is speculating. We do not have a model that works that far back. QM and GR become inconsistent and we need a theory of quantum gravity to make predictions we can test. Until we have testable predictions we simply cannot say what was happening.

[phunk]

I really don't think that is what the mainstream says. It's the most common misunderstanding, but it's not right.

When you take our current understanding of physics and the universe, and run time back towards zero, the physics breaks down before you get to infinity. Infinities are what you see when you run the simulation back to times when our current understanding doesn't work and you get an invalid answer. Some people say that the singularity is what the physics show, but they are either oversimplifying, not mentioning that the physics show that because they are incomplete, or they just don't understand.

We don't know how to model the planck epoch, so we don't know what existed at t=0 before the planck epoch.

[phunk]

Here is a discussion at physicsforums which I have been apart of for a while. The contributors quite clearly note that the current model we deal with is in fact one which arose from an infinitely dense, infinitely small point http://www.physicsforums.com/showthread.php?t=472481

I haven't read the thread yet, but if they say that, they're wrong.

NO model starts with an infintely dense point. The models end with an infinitely dense point, when you take our current understanding of physics and knowledge of the universe and run time backwards.

[Aethelwulf]

NO model starts with an infintely dense point. The models end with an infinitely dense point

Not in the big bang theory it doesn't - it begins with an infinitely dense point - the end of the universe may also posit a singularity, but this isn't what I think you are meaning. By the way, this infinitely dense point is a consequence of the general relativistic equations. Quantum mechanics doesn't normally permit this because of the uncertainty principle - you can't squeeze for instance particles into a dense point - that will define their locations with an infinite amount of accuracy.

[Aethelwulf]

I really don't think that is what the mainstream says. It's the most common misunderstanding, but it's not right.

When you take our current understanding of physics and the universe, and run time back towards zero, the physics breaks down before you get to infinity. Infinities are what you see when you run the simulation back to times when our current understanding doesn't work and you get an invalid answer. Some people say that the singularity is what the physics show, but they are either oversimplifying, not mentioning that the physics show that because they are incomplete, or they just don't understand.

We don't know how to model the planck epoch, so we don't know what existed at t=0 before the planck epoch.

I'd be careful saying ''its not right.''

You seem to be saying, like I have with many people on this forum so far, that the singularity is where many physicists believe the theory breaks down. I agree that many physicists believe this is true, but it is also true there is no ultimate consensus on whether singularities really do exist or not. It is still commonly taught today that as you do run the clocks of time back, you will get to a point of infinite density - now as the BB goes, this is the model it represents, the same point of infinite density and infinite curvature. A completely lawless spacetime region. All big bang models I have read take this artifact of the model on.

[phunk]

Not in the big bang theory it doesn't - it begins with an infinitely dense point - the end of the universe may also posit a singularity, but this isn't what I think you are meaning. By the way, this infinitely dense point is a consequence of the general relativistic equations. Quantum mechanics doesn't normally permit this because of the uncertainty principle - you can squeeze for instance particles into a dense point - that will define their locations with an infinite amount of accuracy.

Yes, in the big bang theory it does. The big bang theory didn't begin with someone saying "what would happen if there was an infinitely dense point", it began with someone saying "what happens if we run the universe backwards". The infinitely dense point is a prediction, a result, a conclusion, not the starting point. Nothing in the BBT is based on that infinitely dense point existing.

[Aethelwulf]

''Some people say that the singularity is what the physics show, but they are either oversimplifying, not mentioning that the physics show that because they are incomplete, or they just don't understand.''

The laws of quantum mechanics do not allow for singularities. This is why we say they break down, because it violates the uncertainty principle. I have questioned why this should scare us off and why we couldn't just use this violation to explain other factors of the theory.

[Aethelwulf]

Yes, in the big bang theory it does. The big bang theory didn't begin with someone saying "what would happen if there was an infinitely dense point", it began with someone saying "what happens if we run the universe backwards". The infinitely dense point is a prediction, a result, a conclusion, not the starting point. Nothing in the BBT is based on that infinitely dense point existing.

Right, this is what you meant.

That's fine, but then you have to start the clock again. You begin from a region where there is infinite curvature, which must invoke infinite energies. In fact, the entire region is singular, meaning every part of it is blown into unimaginable, non-physical concepts.

[Aethelwulf]

And I don't know if you can really say there is an infinite amount of energy you end with - the spacetime we live in surely if it has an ''end'' or a symmetry in time, it cannot be infinite? It'd be a large number sure, but it surely wouldn't be infinite.

[phunk]

You seem to be saying, like I have with many people on this forum so far, that the singularity is where many physicists believe the theory breaks down

That's the original definition of a singularity, where the theory breaks down. The popular definition of a singularity as an infinitely dense point arose because that is the most common prediction of the failed physics, for example in a black hole our physics don't know of a way to stop the collapse, so when you try to apply our physics to the situation in a black hole, there is a mathematical singularity leading to infinities. This doesn't mean that singularity means infinitely dense point, but it's become such a common usage of the word that it stuck.

[phunk]

Right, this is what you meant.

That's fine, but then you have to start the clock again. You begin from a region where there is infinite curvature, which must invoke infinite energies. In fact, the entire region is singular, meaning every part of it is blown into unimaginable, non-physical concepts.

Why would you "start the clock again" from an unknown condition with unknown laws of physics? You would have no way to predict what happens.

[Aethelwulf]

That's the original definition of a singularity, where the theory breaks down. The popular definition of a singularity as an infinitely dense point arose because that is the most common prediction of the failed physics, for example in a black hole our physics don't know of a way to stop the collapse, so when you try to apply our physics to the situation in a black hole, there is a mathematical singularity leading to infinities. This doesn't mean that singularity means infinitely dense point, but it's become such a common usage of the word that it stuck.

To believe in a breakdown of the theory is so far, a personal choice. It could be a prediction we may have to come to embrace. Anyway, I have already said that this is what the theory predicts at these regions. It was, by current belief because our theory tells us, began from an infinitely small region - no geometry existed. So we have now established this be the current mainstream belief, because anyone who says it isn't without any proper answer, they are no more than sharing what they believe in.

[Aethelwulf]

Why would you "start the clock again" from an unknown condition with unknown laws of physics? You would have no way to predict what happens.

You're right, I was just using your analogy to say, we need to begin from somewhere. Saying we wind the clock back doesn't say about looking at things from the positive time-direction --- but whilst we are on the subject, time couldn't have existed at this point - well - our theory wouldn't be able to describe time any way because there is no four metric to speak about spacetime points.

[antoniseb]

And I really don't want to hear the ''this is not what mainstream says'' rubbish. I have read plenty texts on this subject and I can assure you, this is what maintream says. ...

You seem to be trying to put words in our mouths that you can argue against. Look, if you carry most big bang models back before time we can observe things about, then yes... it would go to a geometric point... but the very thing you're trying to say doesn't make sense is the reason we all keep saying it is just models, and the models don't necessarily apply at that time.

[Aethelwulf]

And it's not that ''infinite energy'' has just stuck to the terminology like you stated - there are reasons within the theory we state this. The facts that all parameters are blown into unimaginable proportions at the big bang, we often say things like ''infinite energy'' because this is what the equations predict.

[Aethelwulf]

You seem to be trying to put words in our mouths that you can argue against. Look, if you carry most big bang models back before time we can observe things about, then yes... it would go to a geometric point... but the very thing you're trying to say doesn't make sense is the reason we all keep saying it is just models, and the models don't necessarily apply at that time.

Which is fine... but equally I keep saying, at this point there was no geometry. Just because our theory presents problems being used in the initial conditions should not be meant to be taken this is not the correct approach.

[Aethelwulf]

You seem to be trying to put words in our mouths that you can argue against. Look, if you carry most big bang models back before time we can observe things about, then yes... it would go to a geometric point... but the very thing you're trying to say doesn't make sense is the reason we all keep saying it is just models, and the models don't necessarily apply at that time.

What really got on my nerve today is when I have people tell me this is not what current mainstream theory says - when quite obviously it is.

[phunk]

You're right, I was just using your analogy to say, we need to begin from somewhere. Saying we wind the clock back doesn't say about looking at things from the positive time-direction --- but whilst we are on the subject, time couldn't have existed at this point - well - our theory wouldn't be able to describe time any way because there is no four metric to speak about spacetime points.

If we wind the clock back to the end of the planck time, then we can wind it forward again and it behaves as we expect. If we go into the planck time, we can't do that anymore, because we don't have laws of physics that can describe the situation. The point of infinite density happens beyond the timeframe we know how to describe, to say it actually existed is just a massive assumption that what we do know continues past what we don't know and keeps going to infinity.

[phunk]

Which is fine... but equally I keep saying, at this point there was no geometry. Just because our theory presents problems being used in the initial conditions should not be meant to be taken this is not the correct approach.

The bolded part is one of those unknowns. You're assuming it to be true and drawing conclusions based on that unsupported assumption.

[Aethelwulf]

If we wind the clock back to the end of the planck time, then we can wind it forward again and it behaves as we expect. If we go into the planck time, we can't do that anymore, because we don't have laws of physics that can describe the situation. The point of infinite density happens beyond the timeframe we know how to describe, to say it actually existed is just a massive assumption that what we do know continues past what we don't know and keeps going to infinity.

Good points, but it only strengthens my claim. I already said that we can't deal with time below the Planck time. Yet, BB arose from such a state, we are led to believe. This is mainstream, again.

[Aethelwulf]

The bolded part is one of those unknowns. You're assuming it to be true and drawing conclusions based on that unsupported assumption.

Unknown in what way? Point's are point. There was no geometry...

[Aethelwulf]

You can't dress up a statement ''the BB appeared from a point,'' in any other way than it says on the tin.

[phunk]

Unknown in what way? Point's are point. There was no geometry...

The universe isn't a point at the end of the planck time. We don't know what happened before that, so we don't know that it was ever an infinitely dense point. I'm not sure how to say it more clearly.

[phunk]

Good points, but it only strengthens my claim. I already said that we can't deal with time below the Planck time. Yet, BB arose from such a state, we are led to believe. This is mainstream, again.

Given the bolded part, how can you keep making claims about it?

[Aethelwulf]

The universe isn't a point at the end of the planck time. We don't know what happened before that, so we don't know that it was ever an infinitely dense point. I'm not sure how to say it more clearly.

If there was no length, it must have been a point. That is a mathematical certainty.

[Rhaedas]

You're still running on the assumption that the BB covers the very beginning. It never was meant to cover that, nor does it try to. Someone once quoted that any time you get infinity as an answer, then something is wrong. So the model needs refining, and that's what is being done today. But you don't throw out the model altogether, particularly when it works better than anything else so far proposed.

The best way to argue against a theory is to provide a better theory. So...carry on.

[Aethelwulf]

Given the bolded part, how can you keep making claims about it?

GR is the theory of geometry - this is how we deal with time as a dimension of space. As I have said, just recently, right above, if there are no lengths then you can be mathematically certain you are dealing with a point.

You have such a point as the origin of the mainstream model the BB.

[Aethelwulf]

You're still running on the assumption that the BB covers the very beginning. It never was meant to cover that, nor does it try to.

Yes it does... the BB at this phase is called the high energy phase. It is currently believed by mainstream that this is the phase in which the unification of all forces had been present. The description of reality at no point jumps the singularity and pointlike existence. That wouldn't be the BB if it had.