Philosophically you are correct , But somehow that lump of infinite density must have been there, but we don't know how long was it sitting there . Should we perhaps call it time in negative direction ?
No, then you would be talking about an alternate universe that is seperate from our own that may just have its electrons with an opposite charge. The Big Bang is still seen to be a point of orgin. Time in a negative direction wouldn't bring any energy to the point of orgin of the Big Bang, it would be sent into a negative universe further from that point in that negative direction.
Besides costly experiments, like particle accelerators and space probes, that try to delve deeper into the Planck epoch. Another reason why cosmology is so cool is because the laws of physics, space and time as we know them today weren't applicable.
Given the range of issues raised in this thread, It's probably quite on topic to ask what sense there is to the oft made claim the ('our') universe can sensibly be said to have begun as a point spacetime event, a finite time ago ~ 13.7by, at the big bang, whilst also be currently of infinite size - as one apparently plausible option. Now I know it has been earlier said the word 'effectively' might best be tacked on to 'infinite' re size issue, but that is rarely used elsewhere and it seems by most sources touting that idea, we are meant to take 'infinite' in the literal sense. That creates imo a logical consistency problem. That is, how can any finite expansion rate generate infinite size in finite time? This has nothing to do with the separate GR issue of whether the universe has a constant zero net energy or a continually (perhaps indeterminate) reducing one. One comes across enigmatic, never-quite-expanded-on claims the 'resolution' to this seeming absurdity is that the universe was already infinite in size at the beginning BB event. Huh? What kind of 'beginning' is that? And further, is not the the entirety of 'our' universe supposed to be exclusively encompassed by that point spacetime region we call 'our' BB event? So please, someone venture to explain how this rabbit is pulled from the cosmic hat.
I think General Relativity is your culprit, and this would not be new. It predicts infinities, and hence, its own downfall in singularities, but it is still experimentally tested everywhere in the observable universe. String theory and Loop quantum gravity are theoretical areas of research that attempt to explain the seeming absurdities, however, the technological demands for conducting experiments in these fields can be astronomical. Which sucks.
But isn't the issue here one of explaining the ultimate anti-singularity - infinite sized universe coming into being in finite elapsed time? Indeed to last bit. But it's my impression those two theories or grab-bag of similar hold promise of doing away with a singularity at BB event, but otherwise how would they explain infinite size in finite time? Maybe it's a case of people being too clever with words - just how is 'infinite' really being defined in this context? By equatting an apparent average zero spatial curvature = infinite spatial extent? If so it's an empty formality imo. We know, regardless of whether gravity really balances out overall energy density to zero, there is a huge amount of matter/energy in the observable universe. And on the largest scales believed to be near uniform in distribution. Well in an infinite, Copernican-principle universe that requires an infinite amount of matter be existent within. And all from a point event a mere few byo? Cough cough...
Well if there was no "before" there can't be a "now", there must have been something before the big bang. Now weather or not we find out for sure is probly impossible. As there is no way to tack before and event such as this. Time is infant, it has alwase existed, but space hasn't.
Well can energy ever truly go away though? Momentum is energy, i believe, Momentum can turn in to kinetic, heat, exta. Well there for energy is infinite isn't it? Well in that matter...
One idea that has came up in theoretical physics is that the universe is infinite in size and then repeats itself on out forever, so much so that there would be an infintie number of yourself doing the same exact thing if you traveled out far enough. There wasn't one location in our universe where the Big Bang happened and it happened everywhere at the same time. But I feel like it is a misconception of just the fact that the Big Bang didn't start at a particular location that you could mark in our own universe. I think the Big Bang could have started in a small area, it is just that small area has become all the areas that are present now, and not really that all areas possible had a Big Bang event at once. But, if it was not infinite in size at the moment of the Big Bang, then it started with infinite energy, then there would be a contradiction in that regard. They don't know which of these models is actually true, and so they just explore both possibilities. It is said that a theoretical physicist must explore unkown possibilities.
A truly spatially infinite universe logically requires it to be temporally infinite also, for the reasons already given. Sure but that should not be conflated with the issue of a finite vs infinite sized 'beginning' (likewise for the present). The standard BB+inflation scenario afaik holds that a point spacetime region expanded to become our universe. The everywhere you mention was contained within that embryonic point. A point, or for that matter any initially finite region, cannot expand to infinite size in finite time - period. The last comment is apt if one posits a finite net energy density. As I have said earlier, there is a school of thought - 'universe as the ultimate free-lunch', which claims gravitational energy is somehow a negative one and exactly balances out all the other forms of matter/energy. On a different matter - just how does email notification actually work here? My setting is for instant notification. Got 2 initially per this thread, to which I replied in each case. But no notification since entry #27. Is it not an automated arrangement?
Going through this thread again and see no mention of the accelerated expansion of the current universe or dark energy. And those of course tell us that the universe is not infinite in size.
Big Bang Thoerist are used to thinking of the Big Bang as being infinite. The further you tick back the clock to the moment of the Big Bang, everything starts to become infinite in General Relativity because of the singularity. That is why I proposed the question, " Are we really sure that we can see effects below the Planck Scale having an effect on Big Bang Cosmology?". Almost by definition of the Planck Scale it cannot be detected without infinite energy, so then if something below the Planck Scale did have an effect on Big Bang Cosmology, then it would mean that there was infinite energy at one point in time even though there was no singularity. It would be another infinity that has popped up from the Big Bang, without even considering that there would be different laws of physics because of a singularity. So then it would be easy to just assume that the universe is indeed infinite.
General Relativity predicts infinite density. Not an infinte number of cats licking an infinite and copious amount of chocolate ice cream.
How could you have infinite density without infinite energy? When an infinity comes into question there is no way to work out other values, everything would blow up into infinity! I don't think there is any real method to work with infinities. I would think that Quantum Mechanics predicts it has infinite energy if there are effects seen from the Big Bang that are below the Planck Scale.
I think the real reason why infinities come up in the equations is because Lorenzt Transformations end up in the denominators of the equations. It is not because they put the clock back closer to a time where it would be of infinite density. I don't know if anyone has really shown that the Big Bang has happened at speeds faster than light and that it does not blow up into infinities because of singularities brought up in General Relativity.
As far as I am aware, the question of whether the universe is infinite in size is still open. The fact that the expansion is accelerating doesn't affect the answer to the question of size.
The rate of expansion is exponential over distance. If the universe was larger then the further away areas would have just expanded away faster. SO then there is no way to determine the actual size. You could always say that it is larger and the further away areas just expanded more quickly.
No it is linear. Volume is exponential but the distance is linear (excluding the recent discovery of accleration).
