Tag: Einstein

Question from Andreas:
I know, this may have already been answered, but this piece of information so far successfully hid from my search for knowledge. This is why I’d like to ask a physicist
— Lawrence Krauss — these two questions regarding space and time.

Question 1:
First, as I get it, since Einstein there is no universal time, but a space-time. (Newton was so much easier to grasp for a simple human mind.) Means, space and time are tied together, influence each other and got into existence at the same time which was the big bang. Am I right so far?
Thus space started to exist and to expand since then, as did time — start to exist, that is.

So here comes my first question, because I don’t understand a “what was before” question I sometimes read or am asked (mostly by religious people). I don’t claim to understand Einstein, and I assume only a dozen people on Earth fully do — so maybe I got it all wrong, which is why I have to get this answered.
Is it true that there was no time before the big bang? If so, why are people asking themselves, how and when and why the big bang took place? It cannot be answered (well, the how can be answered to an extent) when there was no time in existence before, so there was no “before the big bang”… or what did I get wrong here?
And the implications? Am I right about shaking my head if people ask the “but what was before” question?!?

Question 2:
Another issue I have with time is distance, the speed of light and our view into the universe. Due to the limitation of the speed of light, we look backwards in time when we look into the universe and see distant galaxies. So we see the past. The farther away a star/galaxy is, the older the image we see. So how do we know if it’s still there? How do we know if a galaxy very far out, in a distant past, isn’t long gone and its stars exploded in nova and supernova explosions? And how far can we look back? I once read that the farthest out we can see is the actual time of the plasma that was “shortly” after the big bang… and we cannot see past that. And that we can see residual “background noise.” If that is true, how can we have a current picture of the universe? Isn’t everything we think about it an extrapolation of a past situation—the only thing that we can see, but we have to calculate how it might have developed since then to now in order to have a full understanding of the universe in its present state?

Isn’t it therefore impossible to have a clear picture of the universe, its number of galaxies, its size etc.? It could be no more than a wild guess, like “yes, we see the images, but we cannot put it together in one map of the current (state of the) universe…”

Those were my two questions.
I am really looking forward to seeing them answered by someone who actually understands what he’s saying, and can even do the calculations (e.g. the time+distance thing), as this gives me headaches for a year or two now, and I just couldn’t find it anywhere else… yet.

The biggest thanks in advance!

Answer by SmartLX:
With the disclaimer that I am absolutely not Lawrence Krauss, I’m happy to help.

Question 1:
There are multiple cosmological models with some kind of Big Bang, and there is a form of time “before” it in some of them. When considering the multiverse hypothesis in particular, you have to consider the possibility that before our system of space-time began others might already have been running. (“Before” in this context relates to causality; if something in another system of space-time caused ours to emerge, you can think of the cause coming before the effect.) If indeed there was no time before the Big Bang, though, then the “before” question is indeed inapplicable, and our ideas of cause and effect have a hard time applying as well.

To summarise in the context of the religiously-charged “what was before” question, we don’t know whether there was a before, if there was a before there didn’t have to be a god in it, and if there wasn’t a before then the Cosmological Argument is nonsensical. The Argument from Contingency is a version that attempts to get around the time-based limitations, but it still has most of the same flaws.

Question 2:
Statistically speaking, we know many stars we can see are long “dead”. Our sun has a total lifespan of about ten billion years, and the larger a star is the sooner it burns out. The best telescopes can pick up images from several billion light years away, and some of the far-out stars are hundreds or thousands of times bigger than the Sun. Even one billion light years out, time will be up for a significant percentage of them since they’ve had to last another billion years since they radiated the light we’re seeing.

So of course our picture of the universe is incomplete. We live in a fortunate time, cosmologically speaking, because the expansion of the universe hasn’t progressed to the point where all galaxies are out of sight of each other, or else we might not know there are other galaxies at all. As it is, we are constantly revising our estimates (and estimates they certainly are) about the contents of the universe based on the information we can gather. Right now the estimate for the proportion of stars with planets around them is rocketing upward as we find evidence of more and more extra-solar planets. Just because we don’t know everything doesn’t mean we can’t learn anything.

I think you misunderstand one significant thing. Our model of the present universe is not an extrapolation from an assumption of the Big Bang; rather our concept of the Big Bang itself is largely an extrapolation from the current state and movement of the universe. Put simply, everything is rushing away from everything else (unless held together by local gravity) so in the past everything was closer, further in the past everything was even closer than that…and at some point beforehand everything was together, and the physicists worked from there. We try to model the current universe based as much as possible on real observations of its present state, rather than extrapolating from an extrapolation – though sometimes we do resort to that.

Feel free to pick up on any of these points in a comment if you think it could be clearer.