The Official Cricketweb Science Thread!

[silentstriker]

As I understand it, our equations only 'work' upto t1=t0+10^-43s. We can't ask the question - "What happened before that time?" because the question presumes that "before t1" is a meaningful entity to talk about.

Yes, that is correct. However, that doesn't imply the question itself is invalid (though it might be) - it just means that we do not have any way as of now to be able to figure out if it is, let alone answer it.

[Ruckus]

I don't think this is true. The questions have been about the nature of the universe at earlier and earlier times but not about the origin of the universe itself. That appears to be a meaningless question to me. What is meant by 'origin' of the universe?

I actually meant it in a more general sense; i.e. anything related to our universe basically. Origins wasn't really the right word.

[silentstriker]

I actually meant it in a more general sense; i.e. anything related to our universe basically. Origins wasn't really the right word.

I see, but I do think it's still an artificial distinction. If other universes do exist, I sure want to find out about them - and not in sci-fi either.

You can say all the universes are part of one big 'macro' universe - it's just we can't visit the others but we can't visit other galaxies either. So it works out to be the same thing, in my mind anyway. I think there'll always be people who are curious about that type of thing. The only thing that would worry me would be if our theories get so far ahead of observation or experimental science that they cease to become relevant scientifically.

[Ruckus]

Yeah it's obviously a very subjective thing.

[shankar]

Yes, that is correct. However, that doesn't imply the question itself is invalid (though it might be) - it just means that we do not have any way as of now to be able to figure out if it is, let alone answer it.

The question is invalid. You have to assume the existence of instants of time prior to t1 before you can meaningfully ask the question of what happened during those instants of time. But we have no reason to presuppose the existence of these instants of time.

[shankar]

I actually meant it in a more general sense; i.e. anything related to our universe basically. Origins wasn't really the right word.

Fair enough.

[silentstriker]

The question is invalid. You have to assume the existence of instants of time prior to t1 before you can meaningfully ask the question of what happened during those instants of time. But we have no reason to presuppose the existence of these instants of time.

Well, we are talking about the plank epoch. The question is invalid because we don't know how to ask it within the framework of the physics that we know - at that point all the forces in our universe were one big unified force and our theories don't know what that would look like. If/when we have GUT and then TOE, we might indeed be able to explore the conditions of that time.

[shankar]

If/when we have GUT and then TOE, we might indeed be able to explore the conditions of that time.

That's the presumption I'm talking about. Why assume that the question will remain meaningful under the new theory?

[silentstriker]

That's the presumption I'm talking about. Why assume that the question will remain meaningful under the new theory?

I'm not presuming that. I'm saying it might be meaningful. We can't make any assumptions about where a theory of quantum gravity will lead us. I doubt it will be to an area of infinite density. The question cannot be dismissed. It may be true that it is meaningless - it is not meaningful at the moment (which I've mentioned before) because we know our theories are incomplete and thus we don't know how to frame the question appropriately in a scientific way. We know relativity breaks down at that point, so it would not be appropriate to make assumptions about space and time based on that theory prior to that time....

[shankar]

Hence the question is invalid at present. The question "What colour is the loch ness monster?" would be meaningful if a theory emerges proving its existence. Till then it's a meaningless question.

[silentstriker]

Hence the question is invalid at present. The question "What colour is the loch ness monster?" would be meaningful if a theory emerges proving its existence. Till then it's a meaningless question.

I am agreeing with you. All I was pointing out was that while the question cannot be asked in a meaningful way but it must be made clear that this is the fault of our physics - our theories are not complete and thus they are unable to frame the question in an appropriate way. If we had TOE, and they conclusively showed that the question was meaningless, then I think it would be more akin to the loch ness monster analogy.

[shankar]

All I was pointing out was that while the question cannot be asked in a meaningful way but it must be made clear that this is the fault of our physics - our theories are not complete and thus they are unable to frame the question in an appropriate way. If we had TOE, and they conclusively showed that the question was meaningless, then I think it would be more akin to the loch ness monster analogy.

The basic issue is this: Do we have any good reasons to predict what a new theory will look like? It might allow legitimate instants of time prior to t1. But it might also allow all sorts of other things that we cannot imagine. For example, "why did pink unicorns exist before t1?" is also a legitimate question according to you since a new theory might make such a question meaningful.

[silentstriker]

The basic issue is this: Do we have any good reasons to predict what a new theory will look like? It might allow legitimate instants of time prior to t1. But it might also allow all sorts of other things that we cannot imagine. For example, "why did pink unicorns exist before t1?" is also a legitimate question according to you since a new theory might make such a question meaningful.

No I think that's false. The question itself is not meaningless. Our theory is wrong and so therefore it is unable to allow us to ask the question. That is what renders the question meaningless - the fact that our physics is incomplete and so we are unable to frame the question properly. That is a very huge difference. We KNOW our theory stops working, so therefore we cannot ask the question properly.

[silentstriker]

It's similar to this: before we knew about extra-solar planets, could we ask if there was water on those planets? No. It's just that we lacked the ability to frame it appropriately because we weren't aware of the existence of planets, let alone water on it. Is the question itself meaningless? No. It's merely premature.

I think we're arguing semantics here, but I do not think it is at all similar to the unicorn analogy. Did something exist before t1 is a valid, if premature, question. In fact, one of the main purposes of a theory of quantum gravity would be to answer if that question is valid - I would say it's one of the more important questions - to give us an impression of a unified force. So no, the question is not meaningless, it's one of the reasons for trying to find a theory of quantum gravity in the first place.

[Spark]

In general, we look for a new law by the following process: First we guess it; then we compute the consequences of the guess to see what would be implied if this law that we guessed is right; then we compare the result of the computation to nature, with experiment or experience, compare it directly with observation, to see if it works. If it disagrees with experiment, it is wrong. In that simple statement is the key to science. It does not make any difference how beautiful your guess is, it does not make any difference how smart you are, who made the guess, or what his name is — if it disagrees with experiment, it is wrong.

Happy birthday to the great man. Would've turned 94 today if he were still alive.