azekeil: (Ulysses_31)
[personal profile] azekeil
First, let me preface this by stating that I'm just a layperson who is quite interested in this sort of thing. I'm just putting some of my thoughts down as they occur to me without any scientific theory behind it.

Having just watched the first two of four episodes of "The Fabric of the Cosmos", they theorise that the the only reason time has a direction is due to the big bang. They also point out that the universe (i.e. space) appears to be accelerating its expansion, and that this is attributable to a majority of dark energy that is unseen (and unknown and not regularly detectable) throughout the universe.

From the first episode (and stuff I remember from A Brief History of Time and other articles) it would seem to me that if the direction of time ("the arrow of time") was caused by the Big Bang, then much like the fact that space is expanding as a result of the Big Bang, perhaps time is continuing to move forward as a result of the Big Bang? Perhaps the perception of the universe continuing to expand is simply a result of the energy from the big bang spreading out and dissipating, and time itself is slowing down making it appear that the universe is speeding its expansion when in reality it could be receding or even slowing down? This could even be enough to account for the dark matter/energy that scientists feel necessary to invent to account for their observations.

I haven't got to the bottom of the nature of time, space and spacetime so this is probably clearly ridiculous for obvious reasons, but I wanted to note it down as an interesting thought, perhaps one I can later come back to refute when I understand more.

Date: 2012-04-15 03:15 pm (UTC)
From: [identity profile] alexmc.livejournal.com
I think you need to ask yourself what you mean by "time itself slowing down".

I can guess what you mean, but is it ever meaningful to say that time goes at one second per second normally, and half a second per second when slowed down? Can time itself slow down?

Date: 2012-04-15 05:41 pm (UTC)
From: [identity profile] azekeil.livejournal.com
Heh, I see what you mean. I think I mean that if the speed of light in a vacuum is constant, then perhaps we've misjudged and what if it's going further in a second now than it was a while ago? I.e. that time is slowing down?

Date: 2012-04-15 09:19 pm (UTC)
From: [identity profile] alexmc.livejournal.com
I've seen the two programs you linked to now.

I don't know. Sounds like it is vague enough for a good SF story.

Date: 2012-04-15 09:47 pm (UTC)
From: [identity profile] azekeil.livejournal.com
Yeah, it's horribly vague. I need to build my understanding of spacetime etc first before seeing if my idea can be easily explained away before going any further :)

Date: 2012-04-15 06:09 pm (UTC)
From: [identity profile] air-bizkit.livejournal.com
Time isn't a thing. Its a human conceptual construct who's only function is to correlate events in relation to each other....as an actual force its a non-entity, unlike say, gravity.

Date: 2012-04-15 07:44 pm (UTC)
From: [identity profile] azekeil.livejournal.com
I don't think time is a force, but nor do I think it's just a construct. For example gravity affects time - they did an experiment where they flew an atomic clock around the world and it was slower than the control atomic clock left on the ground by a few billionths of a second, providing more evidence in favour of Einstein's theory of relativity.

Date: 2012-04-15 08:25 pm (UTC)
From: [identity profile] air-bizkit.livejournal.com
Just speculating here...

But to me, I 'could' read that as "gravity affects the free movement of atomic particles when applied as a force" ... which wouldn't mean 'time' had been affected, just the atom generating the pulse for the mechanism....

Date: 2012-04-15 09:48 pm (UTC)
From: [identity profile] azekeil.livejournal.com
Uh... but by inference everything else on the plane was also a few billionths of a second younger than the stuff on the ground. What do YOU imagine affecting time means?

Date: 2012-04-16 06:17 pm (UTC)
From: [identity profile] air-bizkit.livejournal.com
Time, as I said.. is merely a notional way of describing a number of events correlated to each other..

for example... car moving... car crash... car on fire...mangled steel...

A sequence of events which happens one after the other....... if time was to be affected...... either one of those states could be inserted somewhere else, or perhaps not happen at all.....

Or perhaps for it to be held in one of those states indefinitely.. i.e. stasis..

Date: 2012-04-15 10:36 pm (UTC)
gerald_duck: (lensing)
From: [personal profile] gerald_duck
Being more of a mathematician than a physicist, I approach all this from a symmetry perspective, and feel that thinking yields good results.

The dimensions of space are symmetric: the universe as a whole has no "up". You can orient your X,Y and Z axes any way you like and the laws of physics keep working.

Time is different: it's asymmetric. Specifically, the Second Law of Thermodynamics distinguishes the "past" from the "future" and doesn't work if you swap them over. This also means you can't exchange the T and X axes and expect the universe to keep working in the same way that it would if you exchanged the Y and X axes.

(Personally, I wouldn't say time has a direction due to the big bang; I'd say it has a direction because of thermodynamics. It's the origin and direction of our universe's time axis that are intrinsic to the big bang.)

Frequently, we plot graphs of some quantity against time. Or we draw Feynman diagrams. And so on. Just as we can look at the entire M1 on a road map "all at once", we can look at an exponential decay "all at once" on a graph. To that extent, time's not special.

But our brains themselves are in the universe and subject to the laws of thermodynamics. That's why we treat time differently from space, why working out what's in a cardboard box feels to us like a fundamentally different activity from working out whether it will rain tomorrow. An extrinsic observer wouldn't necessarily be constrained in the same way.

To answer the specific question about how we know time isn't slowing down: we define time to be related to space by the speed of light in a vacuum, c. Yes, it's the "speed of light", but in a more fundamental sense it's the scaling factor between the dimension of time (which we measure in seconds) and the dimensions of space (which we measure in metres). However, thanks to Einstein, we know space-time isn't a straightforward Euclidean space. This results in effects like time dilation, gravitational lensing, etc. but our definition that space and time are related by c remains.

Part of the trouble nowadays is that people go on talking about "distance" and "time" colloquially, but physics has precise definitions of them. "What if time is slowing down" is a question that has some kind of colloquial meaning to us, but is rendered meaningless within the formalisms of modern physics.

Compare with asking someone in IT "what if hard drive storage capacities aren't increasing, it's just that bits are getting smaller?" or asking a geologist "what if plate tectonics isn't really happening, it's just that rulers shrink when you point them at the poles?" (-8

Date: 2012-04-16 10:28 pm (UTC)
From: [identity profile] azekeil.livejournal.com
Bear in mind that space itself is expanding. I've yet to work out whether that means that the absolute distance light travels in a second is changing too, or whether it is going the same distance etc.

This probably all sounds rather confused - it is. This is why I need to really get my head around all this stuff before I can really say anything on the subject that makes much sense :)

Date: 2012-04-16 10:35 pm (UTC)
gerald_duck: (duckling loop)
From: [personal profile] gerald_duck
No, the speed of light in a vacuum isn't changing. It's a constant by definition.

That's how we can tell that space is expanding. Or, more exactly, that's what we mean when we say that space is expanding. You could instead say that the speed of light is changing, but that redefinition of "the speed of light" would have a knock-on effect for the whole of the rest of physics (and the hard sums would turn out to be even harder if expressed in those terms).

Date: 2012-04-18 08:53 pm (UTC)
From: [identity profile] swaldman.livejournal.com
I think there's a certain element here of "there's only so much we can understand about the universe from inside the universe".

I tend to think that things like "space itself is expanding" or "time slowing down" (which make about as much sense as one another) are what the word "metaphysics" should really refer to :-)

Date: 2012-04-18 10:17 pm (UTC)
gerald_duck: (Duck of Doom)
From: [personal profile] gerald_duck
However, there is the metric expansion of space to consider, which is most certainly not metaphysical. And I'd consider it at two levels.

The first is that relativity is hard enough to understand at the best of times and the results get really strange when mind-buggeringly heavy things are moving around while you're trying to do the maths. The fundamental point to take on board is that, while if light travels for a second it's a pretty safe bet it'll end up very nearly exactly 300 million metres from where it started, if it travels for a billion years it's unlikely to end up anything close to a billion light years away, because all the nearby galaxies will now be in different positions and space-time will be differently curved.

The second is that if one does do the maths, there's a discrepancy. To me, present attempts to explain it with things like dark energy positively reek of epicycles all over again. We need another Einstein, or even another Newton, to work out what we're doing wrong. (And then we'll need to start saving up for whatever painfully expensive contraption is needed to test the new theory.)

Date: 2012-04-26 03:17 pm (UTC)
From: [identity profile] swaldman.livejournal.com
I tend to agree, both with dark energy etc and the profusion of particles from supersymmetry, if indeed that's the path things go down... there comes a point at which "We're totally wrong", or at least "there's another layer" becomes the simplest explanation.
Edited Date: 2012-04-26 03:18 pm (UTC)

Date: 2012-04-18 08:49 pm (UTC)
From: [identity profile] swaldman.livejournal.com
Excellent explanation - thank you. It saves me trying to write one that would be much less clear :-)

Date: 2012-04-18 10:22 pm (UTC)
gerald_duck: (quack)
From: [personal profile] gerald_duck
We aim to please. (-8

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