A beginning

[Zero]

If the law of conservation of mass is to be considered, nothing can ever truly disappear, or simply come into being. If we consider this, is it logical, then, to assume that there is no true beginning to things? I mean, if we think about causality, then everything that happens has a cause before itself, so there can be no true first cause. There can't be any uncaused causes, and nothing can just poof into existance, so is it correct to assume that there are perhaps events that led up to the big bang, and probably an infinite chain of causes and effects leading into the past? I just don't see how there can be a true beginning to things... is there an uncaused cause at the beginning of everything? Thoughts, anyone?

[SCRawl]

The Big Bang is one of those special cases -- a singularity. Asking what happened a second before the Big Bang is like asking someone what's a mile north of the north pole. The question itself doesn't make sense.

In other words, there were no events leading up to the Big Bang. It happened, and everything else followed.

[Zero]

Yes, I understand that time doesn't pas near a singularity... one second is infinity... but how did things begin? Did they just... happen? I just can't understand how an expansion such as that would start without outside influence, at least. And events can lead up to the existance of a singularity, so even if time doesn't pass, there may have been things before it... however insane that can sound...

[Kuroneko]

If the law of conservation of mass is to be considered, nothing can ever truly disappear, or simply come into being.

In the context of general relativity, conservation of mass-energy-momentum is not so much a law as a derived theorem, in the sense that the core statement of general relativity, the Einstein field equation, logically implies the conservation law. This law, however, is not quite the familiar "x joules then means x joules now, just with more entropy", but actually states that the covariant divergence of the (stress-mass-)energy-momentum tensor is zero. The mathematical details are not important here, simply that this is a statement about the dynamical structure of spacetime, the curved nature of which prevents the comparison of energy 'here' with energy 'there', and thus is not reducible to a single, scalar number. Simply put, the question "how many joules [or kg or whatever]?" is globally meaningless for most spacetimes (locally, it is well-defined, since that is precisely what the energy-momentum tensor specifies).

A colorful example is an isolated black hole, which is a vacuum solution: the energy-momentum tensor vanishes at every point in spacetime--locally, there is no mass-energy anywhere in spacetime. The jump from this fact to there being no mass-energy globally, however, is unjustified, as this would mean that black holes have no mass (although there is a meaningful way to define global energy in asymptotically flat spacetimes, of which this is one, the point remains that this is still not possible in the general case).

I mean, if we think about causality, then everything that happens has a cause before itself, so there can be no true first cause.

Yes.

There can't be any uncaused causes, and nothing can just poof into existance, so is it correct to assume that there are perhaps events that led up to the big bang, and probably an infinite chain of causes and effects leading into the past?

No. According to the general relativity, it is simpler to assume that time is finite in the past direction and that there is no beginning. The Big Bang is not an event in sense of general relativity, because it cannot be assigned spacetime coordinates, so it does not count as a beginning. In other words, the time interval is open in the past direction.

I just can't understand how an expansion such as that would start without outside influence, at least. And events can lead up to the existance of a singularity, so even if time doesn't pass, there may have been things before it... however insane that can sound...

In the words of Doc, you're not thinking fourth-dimensionally! You're thinking of the expansion as something that needed starting in the first place, while this is nonsensical because time is part of the spacetime manifold. Your question is analogous to "what made time start going forward?". It's quite meaningless, since any change is done is in reference to time, and thus any serious attempt to answer it will lead to a hopeless circularity.

[Darth Wong]

Heavily simplified version: if time had a beginning, then by definition, nothing could have possibly happened before that moment.

[SirNitram]

Here's the problem: You're asking about a beginning, but we understand the term instead as a type of becoming. One or more things become a new thing and we define some point in the change as a 'beginning'. Lumps of iron coalsce into a planet. Organic matter self-replicates into a new lifeform. A tool begins after it's shaped from raw materials.

Whereas this is the real beginning: From henceforth, all was.

[Kuroneko]

Heavily simplified version: if time had a beginning, then by definition, nothing could have possibly happened before that moment.

Yes, but that doesn't quite satisfy the need to explain what is so special about the beginning of time that made time stop there (since GTR is time-reversible). I think it's important to realize that this does not need to be explained simply because there was no beginning-event in the physically meaningful sense.

[Surlethe]

No. According to the general relativity, it is simpler to assume that time is finite in the past direction and that there is no beginning. The Big Bang is not an event in sense of general relativity, because it cannot be assigned spacetime coordinates, so it does not count as a beginning. In other words, the time interval is open in the past direction.

Could this be illustrated by the behavior of y = ln(x) on (0, a]? It "begins" at 0, but is not defined there, and is finite in the x-direction toward 0:

[Kuroneko]

Could this be illustrated by the behavior of y = ln(x) on (0, a]? It "begins" at 0, but is not defined there, and is finite in the x-direction toward 0...

Right, its domain is an open (or half-open, in this case) interval. I consider this distinction important because it removes the necessity for any 'metaphysical special-ness' from such a beginning, be it from theism or some other mechanism, and leaves only known physics (that is not to say that the physical understanding of the Big Bang won't be changed in the future--this is a question of interpretation only).

[wolveraptor]

It's frustrating having to describe the Big Bang without saying "the beginning of time", which logically doesn't make sense. You can't give time a beginning or end, because that implies an outside timescale being used to measure time...or something.

[Zero]

So basically, because all mater that exists in the universe was condensed into one point that can be best described as infinitely small, the effect of the enormous amount of gravity was to make it so that time didn't pass at all? There can't be a cause, because events can't happen if there's no time for them to happen... that's just wacky. It goes completely against common sense. I HATE SINGULARITIES! BLARG! Time doesn't flow at all, or flows backwards, and crap is stretched infinitely long and infinitely thin by tidal gravitational forces, and all because the gravity is so fucking heavy that light itself can't even escape. Sounds kinda boring...

[Surlethe]

[quote="Zero132132"]So basically, because all mater that exists in the universe was condensed into one point that can be best described as infinitely small, the effect of the enormous amount of gravity was to make it so that time didn't pass at all? [quote]

Actually, the big bang singularity wasn't just all the matter rolled up, because then there would be space around the matter. It was space, time, and matter-energy rolled up into nothing. What you're describing is a black hole singularity, which is basically a backwards little sibling of the big bang singularity.

I've heard the behavior of time around singularities described thusly: "Time flows into the singularity once you're inside the event horizon." In other words, once inside the event horizon, the singularity is always in your future.

Since the big bang is just a black hole singularity run backwards in time, you can think of all time as flowing out of the big bang singularity: it is always in your past.

Does it help to think of it like that?

[Zero]

Yeah, but it's still annoying to think that the thing just sort of happened... still annoying. But common sense has nothing to do with physics, so a common-sense notion of cause and effect has no space here. It's just confusing... blarg!

[Lord Zentei]

Think of it like this: the further back you go the shorter the important intervals of time become. So, one second after the big bang, things are happening in tenths of a second. One tenth of a second after the big bang, things are happening in hundredths of a second. One hundredth of a second after the big bang, things are happeining in thousandths of a second and so on and on and on. Thus the further back you go, the more events you can cram into any given amount of time.

There is no begining, no "first cause". Eternity is 14 billion years old.

[Kuroneko]

So basically, because all mater that exists in the universe was condensed into one point that can be best described as infinitely small, the effect of the enormous amount of gravity was to make it so that time didn't pass at all?

No, nothing changes locally. The gravitational time dilation you're referring to is a relative measure--time as measured 'here' vs. time as measured 'there'. Since by all current evidence (WMAP in particular), the conditions near the Big Bang were highly homogeneous, there would be no observable gravitational time dilation, even by hypothetical fiducial observers that could actually survive such conditions. If everyone is slowed down by the same amount, the slowdown loses meaning; if it's unobservable even in principle, it might as well be not anywhere at all.

There can't be a cause, because events can't happen if there's no time for them to happen... that's just wacky. It goes completely against common sense.

You're right, it goes against common sense and is wrong besides. Again, don't think of singularities as points in spacetime--they're more of a lack of spacetime, a 'hole' if you will. This means the Big Bang was not an 'event' in the physical sense of the word.

I HATE SINGULARITIES! BLARG!

Such a reaction is not uncommon.

Time doesn't flow at all, or flows backwards, and crap is stretched infinitely long and infinitely thin ... . Sounds kinda boring...

This one... not so much.

Think of it like this: the further back you go the shorter the important intervals of time become. So, one second after the big bang, things are happening in tenths of a second. One tenth of a second after the big bang, things are happening in hundredths of a second. ...

That would require some universal, observer-independent measure of time, which is unjustified. In the case of the Big Bang, there is nowhere for a second observer to be to observe this kind of speedup, hence it's not physically meaningful.

[Lord Zentei]

Think of it like this: the further back you go the shorter the important intervals of time become. So, one second after the big bang, things are happening in tenths of a second. One tenth of a second after the big bang, things are happening in hundredths of a second. ...

That would require some universal, observer-independent measure of time, which is unjustified. In the case of the Big Bang, there is nowhere for a second observer to be to observe this kind of speedup, hence it's not physically meaningful.

Sorry, it was more of an attempt to convey an intuitive idea of the open interval, and the absence of a begining, not that there was any universal measure of time. I guess it was not a good example.