A few minutes ago I finished watching the final episode of Michio Kaku's four part documentary series about Time entitled Cosmic Time. Kaku claims that before the big bang time was non-existent but I have thought of something, which makes me question this claim.
I believe I am correct in saying that in a vacuum virtual particles are created and destroyed (annihilated, I suppose) all the time. Surely, before the big bang all of space would have been a vacuum? If this is the case then, intuitively, virtual particles would be created and destroyed within it and there would be time, although perhaps 'not as we know it'. This issue is solved if it isn't so simple: if there wasn't a vacuum before the big bang. But if that is the case then I still don't understand and therefore would still like an explanation.
Can anyone help me to understand this issue? Thanks! Nope - a vacuum is SOMETHING. It is 'spacetime' - the 4 dimensional 'arena' in which stuff happens. Without any matter then it can be considered in simple terms by Special Relativity. We know how a photon would move through it, for example, and we can describe on a quantum level the emergence of virtual particles within this spacetime.
At time t=0 there was no spacetime - no arena.
On a simple level a vacuum is space with no matter in it. Pre-big bang then there is no space for there to be any matter in.
(This is one interpretation, of course. There are others, but most accept the General Relativistic conclusion that space and time came into existence at t>0).
I see, thank you, that solves the problem. However, to fully understand this I would like you to take it a little further. If there was no vacuum before the big bang then the possibility for a vacuum is something that has resulted from the big bang, right? Why is this? What 'allows' for there to be a vacuum, or causes its existence? The typical view is that a vacuum is an area of space containing no matter, why then is this affected by, as it seems to me, the existence of matter (as created by the big bang)?
Well, I can give you the noddy version, based on Newtonian physics, or the more advanced version, based on Relativity.
If you want the noddy version then space is 3 dimensional. Those very dimensions came into existence at t=0. Before that there was no empty 'length, breadth and width' for there to be any matter in.
The more 'adult' version is that space and time are 'woven together' into a 'fabric' of the universe - called spacetime. There are 4 dimensions - 3 spatial and 1 temporal. This 'spacetime' was created at the instant of the BB and behaves according to GR - ie it is distorted in the presence of energy (mass). At time soon after t=0 then the whole lot was bent around into a small sphere.* This spacetime does not expand into a vacuum, because there IS no 'outside' for there to be a vacuum in.
There are a couple of analogies usually used here - both have significant failings. Probably the best is the ball of dough (representing spacetime) stuffed with currents (representing matter/galaxies/stars). Stick some energy in (stick it in the oven) and the whole thing expands. Now, imagine the dough as spacetime - it is expanding. The problem with the analogy is that we naturally assume the dough-ball is expanding INTO space/time, whereas in the theory the dough-ball IS spacetime.
The general problem is that we are used to perceiving time and space as 'absolutes'. Surely, we think, a second is always a second, and a metre is always a metre. Not so, says Uncle Albert. The only constant is the speed of light. These other things you THINK are constant - length, breadth, width, time - are all part of a greater whole which itself is constant. Your experience of the different 'constants' is completely dependent on the actual constant - spacetime. The faster you move through space, then the slower you move through time, and vica-versa, but your speed through spacetime is constant - c (the speed of light). Obviously, if you follow it through, this means that your experience of distances/lengths is also relative to your movement through space. There is no universal 'metre' - only for those in a particular frame of reference (ie those moving through space at the same rate).
Some people will tell you that this relativistic picture of the universe is very accessible, if explained correctly. I disagree - it is bleedin' hard to get your head around. Most explanations rely on using analogies (as I did) but the truth is that we are then referencing back to our very partial experience of space and time, and the analogy will inevitably 'break' at some point.
To really get your head around it you have to do the maths. It took me a year to get my head properly around Special Relativity and I'm still working on GR (ie I understand the basic principles of the theory, but the actual maths is pretty fiendish).
I don't know if this attempted explanation helps at all - I found that after a similar explanation by someone trying to help me, years ago, I had to go away and really think about it for quite a long time before I could really 'accept' it.
*You will appreciate that I am using a 3-D analogy for a 4-D topology, which I find impossible to visualise, let alone describe.
There is lot of debates goes on regarding time and space theory, as most of the theories are based on certain postulates not facts.
I haven't replied for a while because, aside from being busy, I've been thinking on-and-off about this. I completely agree with you, Chris, when you say it's hard to get your head around.
So, after some thought, I've cleared up a few questions I had and have a better understanding now. That said, I'm not content with the whole thing yet; two quite large questions that I'm still left with are as follows.
Firstly and most fundamentally: if there was nothing before the BB, what caused it? M Theory solves this problem by saying that the BB was caused when two membranes collided, which kind of makes sense. But this theory is a big jump, and really has no evidence despite the mathematics all working (as far as I know). It appears to me that nothing at all was suddenly given an inconceivable amount of energy, which exploded outward for some reason.
The second major issue I have is that the description you give necessarily gives spacetime an edge, a point beyond which it is no more. Obviously, this is the edge of a 4-dimensional 'object', which can't be imagined. However, it has spacial edges at the extremities of the universe and also an 'edge', in the 4th dimension, at the beginning of time.
Are these legitimate questions, or have I made a mistake in my thinking? Thanks a lot!
Well, yes and no.
The answer to the first question is unknown and, as yet, unknowable. There are some potential 'tests' for string theory - the LHC could provide one, even though that is not its purpose.
Our most successful theory of 'big stuff' is relativity. We know it isn't right (or at least it isn't complete) because it conflicts at a certain point with our other most successful theory of 'small stuff' - Quantum theory.
Standard interpretations of Relativity lead to the assumption that t<0 is a meaningless concept. Superstring theory may supplant this, but as you say we are not yet in a position to test it, so it remains philosophy rather than science.
As for the second part - yes, the problem with the dough-ball analogy is that it does indeed give an impression that there is an 'outside'. The other commonly used analogy is the balloon, which avoids this problem to some extent (but has other problems of its own).
Remember that spacetime is bent in the presence of mass. We can imagine spacetime as the skin of a balloon being inflated. Obviously the total 'surface' is growing, but for an ant crawling around the surface there is no edge - you can travel to infinity and never come across the 'edge'.
Both analogies have their problems - we are trying to visualise a 4-Dimensional 'fabric' in less dimensions, so any analogy will ultimately fail. The maths tells us, however, that there is no 'edge'.
If spacetime has no 'edge' then I see only two options. Either spacetime is infinite in all directions, spacial and temporal, which I don't believe is correct, or that if you arrive at what we could call an edge you would simply appear around the other side, which is comparable with the balloon analogy. I have heard the latter before. If we take the example of a 2D universe (existing on a plane), you can wrap it up into a doughnut shape giving it an extra dimension, but one that is not observable to any 2D creature living in the universe, if they go 'off one side', they appear at the other side. Extrapolating this analogy to our universe gives us the idea that spacetime is shaped like a 4D doughnut.
What I have described relies on an analogy to explain the concept, but actually fits our universe - with no 'edges'. So is this correct?
As for the origin of the big bang, I kind of assumed you would say we don't yet know. I heard somewhere before that the LHC could provide us with proof of String Theory, do you know what proof this would be?
Not a bad way of describing it.
As regards the LHC - if it is possible to detect the formation of micro-black-holes then that would provide strong support for superstring theory I think. The point being that for them to form our model of gravity as an inverse square law would have to be wrong. It would have to increase much faster at the sub-atomic level. Superstring theory offers a model of this, because gravity could be 'shared' between the 6 extra dimensions close to planck distances...
| Bikerman wrote: |
| Well, I can give you the noddy version, based on Newtonian physics, or the more advanced version, based on Relativity. |
'
Just wondering could you give an answer since it is old and wasn't "made" for this sort of questions, wouldn't you get a complete different answer then using the newer relativity.was there a big bang at all?
| yagnyavalkya wrote: |
| was there a big bang at all? |
Judging from all the evidence we have gathered so far... yes. That's why it is an scientific theory.i found this thread to be very interesting! i have always wondered about the universe, or if it even is a universe? it is so much to get your head around, yet somehow, it is my head that is in the way. its hard to believe either side of the argument of does it end. how can something have no end? but at the same time, it is unfathomable that something so vast could simply stop. It is not a wall, a border, or a fence, but simply the end. These thoughts have filled me with the desire to become an astronaut. However, i do not have 20/20 vision, but i think that if i get it corrected surgically, i can become an astronaut. Also, depending on how fast nanotechnology is developed, even blind people will be able to have 20/20 vision, and possibly go up into space. Thats just my 5 cents worth for today.
Ben
its really hard to understand that 'time didn't exist' or even 'space didnt exist' for us because we are so used to it!! that singularity is God no matter what you write below this quoting what I am saying here. 
| supernova1987a wrote: |
| its really hard to understand that 'time didn't exist' or even 'space didnt exist' for us because we are so used to it!! that singularity is God no matter what you write below this quoting what I am saying here. |
[MOD - if you want to talk about God then do it in the appropriate forum (philosophy and religion). The science forums are not the right place - Bikerman] | Bikerman wrote: |
[MOD - if you want to talk about God then do it in the appropriate forum (philosophy and religion). The science forums are not the right place - Bikerman] |
Now that's interesting... Scientific theories that involve God are verboten now? | ocalhoun wrote: |
| Bikerman wrote: |
[MOD - if you want to talk about God then do it in the appropriate forum (philosophy and religion). The science forums are not the right place - Bikerman] |
Now that's interesting... Scientific theories that involve God are verboten now? |
No, certainly not. IF there was a scientific theory involving God here then it would be fine. There isn't. There is simply an assertion that the BB singularity was/is God. That is not a scientific theory (how would you test the assertion?).
[MOD - the point I am making is not that God cannot be mentioned in the Science Forums, but that any such mention must contain some science, otherwise, if it is simply religion or philosophy then there is a more appropriate forum - Bikerman]haha... you would like an explanation to something no one can explain. Sure, some people may have theories, but no one can prove them.
| jabce85 wrote: |
| haha... you would like an explanation to something no one can explain. Sure, some people may have theories, but no one can prove them. |
You don't 'prove' scientific theories. You try to disprove them. Hence if your assertion can be tested (and possibly disproved) then we can say it is a scientific hypothesis. If not then it isn't. | Bikerman wrote: |
| supernova1987a wrote: | | its really hard to understand that 'time didn't exist' or even 'space didnt exist' for us because we are so used to it!! that singularity is God no matter what you write below this quoting what I am saying here. |
[MOD - if you want to talk about God then do it in the appropriate forum (philosophy and religion). The science forums are not the right place - Bikerman] |
Why do scientists like Stephen Hawking, Albert Einstein and Carl Sagan talk about God in their Science lectures or science discussions or science essays? | supernova1987a wrote: |
| Bikerman wrote: | | supernova1987a wrote: | | its really hard to understand that 'time didn't exist' or even 'space didnt exist' for us because we are so used to it!! that singularity is God no matter what you write below this quoting what I am saying here. |
[MOD - if you want to talk about God then do it in the appropriate forum (philosophy and religion). The science forums are not the right place - Bikerman] |
Why do scientists like Stephen Hawking, Albert Einstein and Carl Sagan talk about God in their Science lectures or science discussions or science essays? |
They don't. They talk about God in philosophical speculation if asked, but never as scientists. You are perfectly free to talk about God in any way you like but you do so in the philosophy and religion forum, not in the science forums unless there is a point of science. If anyone wants to post anything remotely scientific involving deities of any description then that is fine - in fact I wish they would.
Anyway I'm afraid the matter is not open for debate - my ruling was in red letters 
