Sensible Erection | The origin of the universe and the arrow of time. Sean Carroll

Wednesday, 17 March 2010

The origin of the universe and the arrow of time. Sean Carroll

quote [ Speaking at the University of Sydney, acclaimed physicist and cosmologist Sean Carroll gives an entertaining and thought-provoking talk about the nature of time, the origin of entropy and how what happened before the Big Bang might be responsible for the arrow of time we observe today. ]

Sweet

[sci&tech] [by germanjulian@9:44pmGMT] [+10 Interesting]

Comments

jaxtraw said @ 10:06pm GMT on 17th Mar
Maybe the whole problem just goes away if you think of Minkowski geometry as a useful calculating aid rather than as a literal description of deep reality. Just a thought.

Naruki said @ 10:34pm GMT on 17th Mar [Score:1 Insightful]
That sounds eerily familiar... Wait:

Maybe the whole problem just goes away if you think of Genesis as an allegory rather than as a literal description of deep reality. Just a thought.

jaxtraw said @ 11:01pm GMT on 17th Mar
You do realise that in that metaphor, you're implying that the spacetime geometry at the basis of relativistic calculation is, like Genesis, entirely wrong?

Naruki said @ 11:33pm GMT on 17th Mar
Well, it wasn't a metaphor, and it wasn't meant as a critique. It's just what I thought of when I read your comment.

jaxtraw said @ 11:34pm GMT on 17th Mar
I just meant that maybe the theory's is correct (I'm quite the Einstein fan myself) but the interpretation isn't. Like, quantum mechanics appears to be correct, but maybe the Copenhagen Interpretation is wrong, that kind of thing.

insanemonkey said @ 6:03pm GMT on 18th Mar
How does that follow?

jaxtraw said @ 8:17pm GMT on 18th Mar
In Naruki's analogy, Genesis==Minkowski Spacetime.

KropperPrime said @ 6:48pm GMT on 18th Mar [Score:-1 Overrated]
See what you made me do now?

I had to upmod you insightful!

Please don't do that again.

f00m@nB@r said @ 12:21am GMT on 18th Mar
What's "deep" and what's "shallow"?

There is only experiment, and predictive power. "Interpretation" is only when you don't have a blackboard to write on so you need pronounceable words.

jaxtraw said @ 12:59am GMT on 18th Mar
Interpretation is at the heart of modern physics, hence Copenhagen Interpretation. Everyone agrees on the equations, but the problem is figuring out what they describe.

f00m@nB@r said @ 1:31am GMT on 18th Mar [Score:3]
Interpretation is at the heart of modern physics

No. I spent my entire adult life in academic physics. Worries about interpretation are confined to an extremely small minority in research physics.

jaxtraw said @ 7:52am GMT on 18th Mar
Well, no wonder they aren't making any progress then.

arctan said @ 3:51am GMT on 19th Mar
Progress toward what? Most physicists don't view themselves as being in the business of answering broad philosophical questions asked by laymen.

cold_water said @ 4:03pm GMT on 18th Mar
Bend over, I'll demonstrate the difference between deep and shallow!!

arctan said @ 3:50am GMT on 19th Mar
The philosophical problem of "Why is there an arrow of time?" doesn't go away at all. All that happens is you take away our framework for addressing and possibly answering the question.

MelloHippo said @ 11:14pm GMT on 17th Mar
I've always thought that whatever constancy we get from time has some relation to the constant expansion of the universe. What I didn't know is that the universe's expansion is speeding up. However, I still feel partly correct since he says the arrow of time is directly related to entropy, and expansion is a large part of the universe's entropy.

metternich said @ 11:22pm GMT on 17th Mar
I suppose I've always thought that, too but never put it into words.

MelloHippo said @ 11:35pm GMT on 17th Mar
Glad I'm not the only one. I even thought that idea was a popularly held one until I mentioned it to an astrophysics teacher one time and she looked at me like "uhh... what?"

rndmnmbr said @ 11:50pm GMT on 17th Mar
Time? Time is easy. We're only 3rd dimensional beings, capable of experiencing small slices of the fourth dimension as we move through it. Entropy just so happens to be the direction we're traveling. We can't reverse entropy because we can't control our position in the fourth dimension.

Naruki said @ 1:05am GMT on 18th Mar
Hah! No such thing as a small slice. Time either, for that matter.

MelloHippo said @ 2:01am GMT on 18th Mar [Score:1 Insightful]

insanemonkey said @ 5:58pm GMT on 18th Mar
I've seen "time doesn't exist" sprayed like that in a few place. Where was this? Looks like the UK...

I wanted to write "since when?" underneath...

serenitynow said @ 6:52pm GMT on 18th Mar
Obviously, you don't have time. Time is relative. I spent three years in Wellington, NZ, one weekend.

Naruki said @ 11:23pm GMT on 19th Mar
With the relatives?

Spaceloaf said @ 3:34am GMT on 18th Mar [Score:1 Interesting]
You didn't answer anything. The question is why can't we control our position in the 4th dimension.

If you take the arrow of time to its natural conclusion, eventually the arrow will disappear as the universe reaches its entropy equilibrium.

It's just like when you trace the position of the stars back in time, you conclude that there must have been a big bang. If you trace entropy back in time, there must have been some point where entropy was zero. Obviously that seems highly unlikely, so there must be some explanation for the imbalance we see today.

(Another question along these lines is why is antimatter so rare in the present.)

rndmnmbr said @ 4:36am GMT on 18th Mar
We can't control our position in the fourth dimension because we're not fourth-dimensional. And we're not moving through it - we're being moved, by a fourth-dimensional gradient called entropy. Our movement along this gradient is what we call time. When we come to the end of the gradient, there will no longer be something called time. There's no more motive force to our movement.

Spaceloaf said @ 5:54am GMT on 18th Mar
...because we're not fourth-dimensional.

That's a nonsensical statement. There's nothing that exists in this universe that is not four dimensional.

Let's ignore time for a second. It's impossible to make an object that is truly only two dimensional in our universe. All matter particles and force particles in our world interact in three spacial dimensions, and in the more general case with time.

As to entropy being a "gradient" for time, that is already well established. There's nothing insightful about saying that.

As I said in my post above, the interesting things are what happened to cause the gradient in the first place, and what will happen when the gradient disappears (e.g will causality even exist anymore). The very fact that we only know how to define time through entropy is what creates these questions.

rndmnmbr said @ 6:29am GMT on 18th Mar
We'll have to agree to disagree then. It seems logically obvious that we are only three dimensional. The whole concept was fairly well explained in Flatland.

arctan said @ 3:56am GMT on 19th Mar
We're not actually three-dimensional. We're four-dimensional. If you read the preface to most editions of Flatland published today you'll see the author acknowledge that. A. Square politely tells us that he isn't including time in his list of "dimensions" and that if you do include time then obviously Flatlanders are "three-dimensional" because they do, in fact, exist in and experience time.

We, too, are four-dimensional beings. We just *perceive* the dimension of time differently from the dimensions of space. This whole malarkey about us "moving through" time needs to be dropped -- nothing physically "moves through" time, we just have conscious minds that *perceive* the world as one instant of time after another, but in terms of what we actually *are* we're static, unmoving structures in space-time just like everything else is. The "motion" of time is, from a purely physical standpoint, illusory -- what needs to be explained is our minds, and why our minds work in such a way that we perceive an arrow of time (because our minds are dependent on chemical processes that are dependent on entropy -- but why?)

He also says that Flatlanders must also be "three-dimensional" in the purely spatial sense, in that Flatlanders have a very, very thin "thickness" to them -- to a Spacelander they're like very thin pieces of paper. They're unaware of their "thickness" only because everything in what they perceive as their "world" is equally thick. That's what the person you're replying to was getting at -- assuming, for instance, that string theorists are right and the universe has extra dimensions in it that we don't see, we probably don't see them because they're "compressed" the way the third dimension is for a Flatlander -- as though we're all moving on the surface of a sheet of paper but the paper also has a "thickness" to it that we can't perceive because the "thickness" is so thin we can't move up and down in it (so to speak).

serenitynow said @ 1:07am GMT on 19th Mar
quote [That's a nonsensical statement. There's nothing that exists in this universe that is not four dimensional.]

You're saying time is a fourth dimension?

How many seconds in a mile?

Omegaphobic said @ 11:21pm GMT on 20th Mar
Technically, 1/186282397.

That was a silly rhetorical question, wasn't it?

serenitynow said @ 11:08am GMT on 22nd Mar
Not at all. Time is relative to motion. Not distance.

quote[Technically, 1/186282397]

That's a silly answer, isn't it.

loomspace said @ 11:56pm GMT on 17th Mar
Who was his audience? Seems like a pretty basic 'Here are some observations of the universe, now in summary... we don't know. Buy my book.'

f00m@nB@r said @ 1:32am GMT on 18th Mar
Ain't physics fun? You get all these wannabe scientists who couldn't hack the classes back in school lapping this fuzzy stuff up.

lilmookieesquire said @ 9:05am GMT on 18th Mar [Score:1 Funny]
Ith thath wath onth my tongue?

mrcucumber said @ 1:34pm GMT on 18th Mar
I recently went to the Hayden Planetarium (again) because friends were in town. Passed through the "big bang" theater. Geez, talk about 4 minutes of fuzzy....

arctan said @ 3:58am GMT on 19th Mar
At least when they're ignorant they know they're ignorant, which is a lot less common in "softer" subjects like literary criticism or political science or history or (as we all know here) economics.

pleaides said @ 8:17am GMT on 18th Mar
This stuff is awesome, but it explodes my brain, and so doing totally ruins the carpet.

KropperPrime said @ 7:16pm GMT on 18th Mar [Score:1 Informative]
I agree, but you need a science-proof carpet.

serenitynow said @ 3:42pm GMT on 18th Mar
Well, Einstein proposed that in sending a straight line out into space(time) it would eventually return on itself. This would make time cyclical.

When we accept the first law of conservation of energy - that energy can't be created or destroyed - we can propose all energy here has always been here in some form or other, going through its changes (often catastrophic) according to the laws governing the universe.

Under this premise, time becomes 'eternal'. No beginning or end. Just repeating points in the process of time, points of action and reaction (Newton's law). This releases us from the 'linear time' argument which, unless you believe God wished everything into existence from nothing, doesn't satisfy the 1st law of thermodynamics.

So, the process of change over time becomes something that cyclicly repeats, according to Newton's law.

insanemonkey said @ 6:02pm GMT on 18th Mar
"Well, Einstein proposed that in sending a straight line out into space(time) it would eventually return on itself. This would make time cyclical."

...and would make the universe torus-shaped, which I find quite interesting.

serenitynow said @ 6:48pm GMT on 18th Mar
Why do you think it makes it torus shaped? Does infinity have a shape? I can understand the universe shaping things within it, but the universe being 'all that is' would be infinitely shapeless.

Misanthrope said @ 9:34pm GMT on 19th Mar
How would you move along or across something without a shape? More so how can something in existence not have a shape?

insanemonkey said @ 1:22pm GMT on 23rd Mar
On a sphere (like earth) if you were to move far enough in any direction you will eventually end up where you started. In a torus shaped universe you can move in any direction and you will evntually end up where you started. Not sure I can describe it better without waving my hands around or drawing pictures...

serenitynow said @ 2:16pm GMT on 23rd Mar
"In geometry, a torus (pl. tori) is a surface of revolution generated by revolving a circle in three dimensional space about an axis coplanar with the circle".

You've described your theory well. I understand it. But what you appear to have described is the regulation/ relativity of motion within infinite space. My idea is that infinite space itself has no geometric form, no boundary, no physical perimeter to describe it. It is space. But that is just the point I'm at with it.
The question I'd pose to you is - If the object A you sent into motion in space at 45degs, and then object B set off at 35degs, would they eventually describe the exact same path?
To me, the answer to that would define the next set of logic rules/steps toward the next question about the shape of space.

insanemonkey said @ 3:19pm GMT on 23rd Mar
It would appear I was arguing a half-remembered and barely related idea of a hyperdonut that I read about in Hyperspace by Michio Kaku.

Note to self: don't discuss advanced physics that you can't remember properly and don't really understand just after waking up.

To answer your question though...if I say "no", what then?

serenitynow said @ 6:40pm GMT on 23rd Mar
quote [On a sphere (like earth) if you were to move far enough in any direction you will eventually end up where you started. In a torus shaped universe you can move in any direction and you will evntually end up where you started.]

It just struck me what you said.
Why does the universe need to be torus shaped to achieve the same thing we do circumnavigating the surface of a globe (the earth )- returning to the same start point from any direction?
The only difference I can see is we're travelling on a surface, using the globe model.

Anyway, this is my surmising -
if you say no,

1/ Hypothetically, if the two trajectory objects (35 & 45 degs) do not eventually refer onto the same path, it suggests time and motion (e.g. a moving object) operates independently of space time - still accepting space is considered curved, which will bring both objects back to their same starting point at different times.

If yes,

2/ If the trajectory objects do refer to the same path, then time and motion (e.g. the moving objects ) and space time are interdependent/the same. The objects will be assimilated by (as against just a force operating on them) the curve of space time, making it interdependent with time and motion.
This idea is an allegory of the 'weak equivalence principle' (http://en.wikipedia.org/wiki/Equivalence_principle#The_weak_equivalence_principle) a keystone to Einstein's theory of relativity.
The simplest way to test the weak equivalence principle is to drop two objects of different masses or compositions in a vacuum, and see if they hit the ground at the same time (Galilieo's test of Aristotle's theory).
As space is a vacuum, and if we replace mass with position, I suspect a form of this principle applies.

So, where does that leave 'does the universe have a shape?

If 1/ no, paths don't converge, it suggests to me we have an 'open' universe. It's laws/forces, while influencing what's in it, don't give it shape.

If 2/ yes, paths converge, it suggests to me the universe is 'closed'. It has shape, and it's laws/forces determine everything within it.

.

insanemonkey said @ 1:24pm GMT on 23rd Mar
"does infinity have a shape"

Well I think the torus idea is reliant on there not being infinite space, but rather an infinitely loop bit of space. So you can move forever in any direction and you will never reach the edge. I've only just woken up, not sure if this will make any sense!

pelon said @ 9:25pm GMT on 18th Mar

bigjohnson said @ 11:37pm GMT on 18th Mar
i don't understand the reverse arrows in his theory.

he's saying that things generally don't go from high entropy to low...but isn't that the same idea as a reverse time arrow?

J-Loser said @ 12:18am GMT on 19th Mar [Score:1 Funny]
According to Einstein, Chuck Norris can roundhouse-kick you yesterday.

bigjohnson said @ 12:21am GMT on 19th Mar
or he already did, tomorrow

swiggy said @ 3:11am GMT on 19th Mar
see also:

swiggy said @ 3:57am GMT on 19th Mar
tell you what, i'm just gonna post this.