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"It so happens that "negative time", or even time t=0, is equally as meaningless as Elephant Time or Verb Time. They are all undefined."

I'm very curious about the assertion that t=0 is meaningless. Is this the conclusion of a line of reasoning, or is it an axiom assumed in order to make the theory work?

It looks like the latter to me, but that may just be because I'm not familiar with the literature and concepts.

In the standard theory, t=0 is a "singularity." Energy density becomes infinite, for example, at t=0. What that really means is that t=0 is undefined in the same sense that 1/0 is undefined.

Consider the function 1/x. For all positive x, 1/x is defined. As you approach x=0 from the right, 1/x approaches infinity. Same thing for the density of the universe. But the point 1/0 itself is undefined, even though the limit is well defined from the right. Likewise, t=0 itself is undefined, even though the density is well defined for all times greater than t=0.

I wouldn't really consider this an "assumption." It is actually a consequence of assuming that the universe is expanding in accordance with the law of gravity and that energy is conserved. The only way to do it is to construct a "metric" ( http://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre... ) where a bunch of parameters are undefined at t=0, but well-defined thereafter.

Thanks for the explanation. I think part of my confusion arises from the (apparently) mistaken idea that t=0 is equivalent to "the first moment of time." But it looks like t=0 is closer to "before the first moment of time". In a certain sense, that's a contradiction, because you can't have "before" time, but in another sense it's the only way to speak of that which (logically, not necessarily chronologically) precedes time.

Would you say that's a decent summary, given that I'm translating from scientific terms to more philosophical terms?

> Thanks for the explanation. I think part of my confusion arises from the (apparently) mistaken idea that t=0 is equivalent to "the first moment of time." But it looks like t=0 is closer to "before the first moment of time". In a certain sense, that's a contradiction, because you can't have "before" time, but in another sense it's the only way to speak of that which (logically, not necessarily chronologically) precedes time.

Yes, I think that's right. It's more accurate to say that there was no first moment rather than that t=0 was the first moment. Reconciling that with the fact that time is nevertheless finite is an important part of understanding the big bang.

To put it mathematically, the set of points of time is open on the left end. The set of times is this: (0,\infty). And not this: [0,\infty)

Edit: By the way, when I say that time is "finite", I mean finite from now into the past. Not finite from "start" to "finish". The standard cosmological model with dark energy have time being infinite from "start" to "finish"

Yes, exactly, in the standard theory, the Universe is undefined. :-)

Have fun with that and your "dark energy." I will continue to laugh at you. :-D (And will get downvoted as a result, but it's worth it.)

It so happens that "negative time", or even time t=0, is equally as meaningless as Elephant Time or Verb Time. They are all undefined

But Hammer Time is still okay, right?

I understand perfectly well your point of view, you don't need to lecture me on it, I've heard it many times before, as I alluded previously.

  The universe did not come from nothing. Consider the following two claims:
  * The universe has a finite age.
  * The universe has always existed.
  Both of these claims are true.

This is a perfect example of the reasoning I described, thank you.

Here's the other bit:

  [1] It so happens that "negative time", or even time t=0, is equally as
  meaningless as Elephant Time or Verb Time. They are all undefined.

I understand this concoction you've formulated, but it isn't very convincing. There's absolutely no evidence that this interpretation of the word "always" is true, and further, it's a violation of Occam's Razor. It would be simpler to take "always" literally, but you are in fact, through what amounts to simple verbal trickery, changing its meaning.

You can state it's "meaningless" to speak of t=0, but you provide zero backup for this, other than it satisfies your fantasy.

You can state it's "meaningless" to ask what happened X minutes before the Big Bang, but again, this is only in the service of satisfying your fantastical theory.

Meanwhile, back in the Universe and the realm of Logic, it's very meaningful to ask what happened at "t=0", because such a state did exist. It even existed in your Big Bang Theory, which states there was an "initial state."

It is highly improbable (if not provably impossible), that such an "initial state" is realistically feasible, and it certainly violates Occam's Razor. Your "initial state" has no explanation. You in fact vehemently object to any attempts at an explanation, deriding them as "undefined." This is faith in its purest form.

Sorry, but I think you are a very religious man and don't realize it. Thank you, however, for the wonderful illustration of my point, I can use it as a historical example of the problem. :-)

To those downvoting me, you're welcome to speak up. This is a game of logic, and I was hoping that this community could keep the religious knee-jerk reactions down to a minimum. :-\

FWIW, I did not downvote you. But you still do not seem to comprehend the fact that the standard theory assumes time is finite. In order to disprove such a theory, you cannot just assume that time is infinite, because you are assuming the conclusion. If you convince me that you actually understand this, I will continue responding to you.

FWIW, I did not downvote you.

I know, HN doesn't allow downvoting of responses. :-p

But you still do not seem to comprehend the fact that the standard theory assumes time is finite.

Really? I thought I was very clear in demonstrating that I understood this through and through, hence the accusation of faith. I did not simply use an assumption that time is infinite as disproof, in fact I did not disprove BBT at all in my response, but merely gave reasons why I thought it was extremely unlikely to have a start.

You sound like a crackpot. You don't sound like you understand physics. You also sound cranky. If you want to have a discussion, you should stop using grandiose language.

itistoday, do you agree that atomic clocks appear to run more slowly as the gravitational field gets stronger?

Yes I do, though shouldn't that line of reasoning be another strike against some of the tenants of the BBT? If you have an infinitely dense object that represents everything, time shouldn't pass, so how could anything have ever gotten anywhere?

Again, no t=0. It never was "infinitely" dense, it just approaches this limit.

You said: it certainly violates Occam's Razor. Your "initial state" has no explanation. You in fact vehemently object to any attempts at an explanation, deriding them as "undefined." This is faith in its purest form.

Occam's Razor says to go with whatever the simplest model is that accurately predicts everything, not just the simplest model.

The Razor is a rule of thumb. If you have multiple theories / models that all accurately explain all observed phenomena, then they're all correct. In fact, since they make the same predictions, they're all equivalent. Occam's Razor basically says "don't waste time with theories that accurately explain the world but also make unfalsifiable / meaningless predictions."

Smugness doesn't constitute an argument. For any statement you make, I can respond "Ha, I knew you'd say that, how naive and predictable!" I can also add "I perfectly understand your position" despite giving no one any reason to believe this is true.

If our physicist friend didn't provide "backup" for his points, it's probably because he's just trying to set you on the right track. You can't reasonably expect someone to lay out the experimental results of every test we've ever run that has led us to assert TBB. And if you're going to persist in claiming that you understand the theory anyway despite all evidence to the contrary, I really doubt it would make any difference.

I am curious how you became so very confident that you are an enlightened genius and all physicists are naive and irrational fools. Especially since physics arrives at it's theories by empirical evidence whereas you seem to arrive at yours by proclaiming inapplicable truisms.