Register to reply

Why does time require matter ?

by phinds
Tags: matter, require, time
Share this thread:
enosis_
#163
Dec15-13, 11:54 AM
enosis_'s Avatar
P: 120
BTW - sorry to post on an old thread - saw it on FB.
phinds
#164
Dec15-13, 12:53 PM
PF Gold
phinds's Avatar
P: 6,509
Quote Quote by enosis_ View Post


IF the universe ever stops expanding - THEN shouldn't gravity begin to re-gather all of the lifeless mass into a single point again?
There is no reason to believe that this can happen. That is, there is nothing to suggest that the universe is going to collapse.

Also, your "single point" concept is nonsense. The original universe was a dense hot plasma of unknown size but no reputable cosmologist believes it was a point. If might even have been infinite.
enosis_
#165
Dec15-13, 01:14 PM
enosis_'s Avatar
P: 120
Quote Quote by phinds View Post
There is no reason to believe that this can happen. That is, there is nothing to suggest that the universe is going to collapse.

Also, your "single point" concept is nonsense. The original universe was a dense hot plasma of unknown size but no reputable cosmologist believes it was a point. If might even have been infinite.
Ok - no single point at big bang.

If there is no longer expansion, why wouldn't gravity re-gather mass - somewhere/anywhere? Why would everything stop - wouldn't gravity still exist somewhere?
phinds
#166
Dec15-13, 01:55 PM
PF Gold
phinds's Avatar
P: 6,509
Quote Quote by enosis_ View Post
Ok - no single point at big bang.

If there is no longer expansion, why wouldn't gravity re-gather mass - somewhere/anywhere? Why would everything stop - wouldn't gravity still exist somewhere?
I guess what I should have said explicitly was, there is no reason to believe that expansion will stop. In fact, there is every reason to believe that it will continue and will continue to accelerate.

This means that your question is equivalent to saying "if the laws of physics stopped applying, what would the laws of physics say about <put in anything you like>?"
Naty1
#167
Dec15-13, 03:40 PM
P: 5,632
I post a few papers here because they gives some additional perspectives I did not see in this thread....
that gravity can be interpreted as a holographic phenomena of degrees of freedom, entropy, temperature.....for an expanding cosmological horizon...

The following paper was referenced in a previous discussion in these forums:
[I did not record the ARXIV link]

Emergent perspective of Gravity and Dark Energy
T. Padmanabhan


Decades of research have shown that one can associate notions of temperature and
entropy with any null surface in a spacetime which blocks information from certain class
of observers….. Any observer in a spacetime who perceives a null surface as a horizon will attribute to it a temperature...Well known examples of such null surfaces are black hole horizon and cosmological event horizon in the de Sitter spacetime…….
my own note: Thus [by inserting a few hbars on each side of] a gravitational equation, the gravitational field equation, evaluated on the horizon now becomes a thermodynamic [expression… allowing us to read off the expressions for entropy and energy.


If Chronos' post [was it #124?edit: #104 ] is right, gravity,hence time appear eternal....

Thermodynamics of Spacetime:
The Einstein Equation of State
Ted Jacobson 1995
http://arxiv.org/abs/gr-qc/9504004

Summary:
In thermodynamics, heat is energy that flows between degrees of freedom that are not macroscopically observable. In spacetime dynamics, we shall define heat as energy that flows across a causal horizon. it is not necessary that the horizon be a black hole event horizon. It can be simply the boundary of the past… a null hypersurface Can derive the Einstein equation from the proportionality of entropy and [boundary] horizon area together with the fundamental relation _Q = TdS…This thermodynamic equilibrium relationship applies only when a system is in “equilibrium”, not where the horizon is expanding, contracting, or shearing. In the case of gravity, we chose our systems to be defined by local Rindler horizons, which are instantaneously stationary, in order to have systems in local equilibrium. Classical General Relativity know[s] that [the] horizon area would turn out to be a form of entropy, and that surface gravity is a temperature.....
Our universe, of course, is not pure de Sitter but is evolving towards an asymptotically de Sitter phase. It is therefore natural to think of the current accelerated expansion
of the universe as an evolution towards holographic equipartition…… we can describe the evolution of the accelerating universe entirely in terms of the concept of holographic equipartition.
so it appears in this sense entropy never goes to zero....meaning neither does gravity nor time.

I have no idea what all this means! Time for football.
julcab12
#168
Dec16-13, 01:02 AM
P: 157
Quote Quote by phinds View Post
I guess what I should have said explicitly was, there is no reason to believe that expansion will stop. In fact, there is every reason to believe that it will continue and will continue to accelerate.
"
... I'm quite weary when it comes to eternity on both ends due to the fact that it's not happening locally. Considering energy as a process of phase transformation and conversion at which each phase has it's unique behavior. On the side-note. I also agree that expansion is what we can come up 'directly' from the data and for obvious reasons. But I believe that at one some state in time that behavior(expansion) will be converted to a different behavior(?) in a manner of phase transition. Fortunately, When i tried to search that idea. I've stumble upon an article on 'phase transition' - cp-3 origins program. They're suggesting prior to their computations (I have no access) that some state of collapse IS happening (not the same as crunch). I'll remain skeptic on eternal inflation. I guess i have a problem with infinity. I don't know. It's just me.^^

http://sdu.dk/en/om_sdu/fakulteterne...psing_universe
phinds
#169
Dec16-13, 08:00 AM
PF Gold
phinds's Avatar
P: 6,509
Quote Quote by julcab12 View Post
... I'm quite weary when it comes to eternity on both ends due to the fact that it's not happening locally. Considering energy as a process of phase transformation and conversion at which each phase has it's unique behavior. On the side-note. I also agree that expansion is what we can come up 'directly' from the data and for obvious reasons. But I believe that at one some state in time that behavior(expansion) will be converted to a different behavior(?) in a manner of phase transition. Fortunately, When i tried to search that idea. I've stumble upon an article on 'phase transition' - cp-3 origins program. They're suggesting prior to their computations (I have no access) that some state of collapse IS happening (not the same as crunch). I'll remain skeptic on eternal inflation. I guess i have a problem with infinity. I don't know. It's just me.^^

http://sdu.dk/en/om_sdu/fakulteterne...psing_universe

I see your concept as unsupportable personal speculation and the paper you referenced seems to be nonsense. Just a couple of the things in it that jump out as being clearly wrong are:

(1) the statement that physicists believe that a collapse would put the universe "into a small, super hot and super heavy ball" . I've never seen it proposed by any serious cosmologist that a crunch, if there were one, would end up in a small ball because that implies that the universe STARTED as a small ball and no one believes that to be the case.

(1) the statement that the phase change would occur in one place and spread out at the speed of light and thus cause the collapse of the entire universe. Since the entire universe is believed to be much bigger than the observable universe and even things out at the edge of the OU are receding at about 3c, clearly such expansion would at most have an effect on a relatively small localized bubble, at most the size of an observable universe, and could not possibly cause the collapse of the entire universe because it would be causally disconnected from the rest of the universe.
julcab12
#170
Dec17-13, 01:12 AM
P: 157
Quote Quote by phinds View Post
I see your concept as unsupportable personal speculation and the paper you referenced seems to be nonsense. Just a couple of the things in it that jump out as being clearly wrong are:

(1) the statement that physicists believe that a collapse would put the universe "into a small, super hot and super heavy ball" .

(1) the statement that the phase change would occur in one place and spread out at the speed of light and thus cause the collapse of the entire universe.the entire universe because it would be causally disconnected from the rest of the universe.
I never had the math to begin with and i understand it's against the rules. So i'll cut right away.

Furthermore. I'm more speculating than they did. I'm just curious how they come up with such math(no google luck) to proposed that prediction. I can agree that the universe expansion is still accelerating(timescale not speed) according to latest consensus. I only mentioned a change in 'state'. Will it expand to infinity after the era of blackholes(exemption photon decay) resulting to extremely low energy state?- It is really hard to cut down 2 possibilities. It can either go ripping forever based from our present understanding on dark energy assuming that it will remain stable or constant forever. Or chill according to some model. Everything so far changes in state why does dark energy an exemption?

I'm just curious how they come up with such equation and radical concept of crunch. Since using comparison on 1st and second Friedman equation. We can easily dismissed the illusion of negative pressure i.e spatial curvature set to zero in the 2nd equation for convenience. They might used some exotic things to make it work which i'm speculating BTW.
Johninch
#171
Dec18-13, 03:15 PM
P: 96
Quote Quote by phinds View Post
I have read in serveral posts here that the concept of time in a total void is meaningless. That is, many scadzillions of years from now, assuming the expansion continues and black holes evaporate, and all goes REALLY dark (yes, I'm talking about a LONG time), the concept is that time loses its meaning because there's no way to measure it.

This really is perhaps one of those silly semantic arguments that I usually do not care for but this one is bugging me for some reason.

I GET completely the fact that you can't MEASURE time without matter but the concept that time just stops passing doesn't make sense to me. It is a somewhat pointless distinction, since even if time goes on, nothing HAPPENS. It's just the concept that "time stops" that bothers me and that SEEMS to be what I'm hearing from some of the threads here.

I'd appreciate any comments anyone has on this? Do you think time doesn't exist if you can't measure it because there's nothing to make clocks out of (and even no subatomic interactions to measure your ticks by) ?
I think that it is less an argument about semantics and more an argument about reality. Semantics would not be worth discussing. Your question may be over the border into philosophy, but I don’t see anything wrong with that.

First off, the scenario you paint with the long-term continuation of expansion does not produce a "total void". So long as there is some energy in some form, something must happen and that requires the time dimension.

If the universe ceases to exist, then spacetime vanishes with it. The multiverse theory says that there can be other universes with their own spacetime, perhaps operating under other laws of physics. They can be successors of this universe or they can be existing in parallel. But to get a continuation of time, there would have to some kind of link between the universes. There would be a contînuation of time if this universe is eternally waxing and waning.

Someone said that time should not be equated to the interval between events. I agree with this for two reasons: 1) events themselves take time too, and 2) I doubt that intervals exist anyway. The measurement of time is purely a comparison exercise, just like the measurement of the 3 dimensions of space is a comparison exercise. If space and time are inseparable, then the speed of light is a good yardstick for all of them.

So what about intergalactic space? It is supposed to contain dark energy which causes space to expand, and this requires time too. I don’t see how time can stop, so long as the universe contains something, which it must.

The scenario you paint of a very low density universe would nevertheless allow measurement to take place. That it is actually measured would require a measuring agent in this universe or in another one. In other words, the universe will always be measurable, so long as it exists. If time is inseparable from space, time is also inseparable from the existence of the universe.

Your reference to “time loses its meaning because there's no way to measure it” is understandable, but in the painted scenario, the universe wouldn’t have much meaning either. It probably never had a meaning.

That's my opinion.

.
phinds
#172
Dec18-13, 04:18 PM
PF Gold
phinds's Avatar
P: 6,509
Quote Quote by Johninch View Post
...
Someone said that time should not be equated to the interval between events. I agree with this for two reasons: 1) events themselves take time too ...
You misunderstand the exact meaning of the word "event" as used in physics. Your use is the standard English language meaning. In physics, an event is an idealized exact point in spacetime. Anything with duration (or length for that matter) is not an event, it is a set of events.


Register to reply

Related Discussions
How much time require to heat..? Introductory Physics Homework 5
Do theories of quantum gravity require that space-time is a lattice? Cosmology 2
Am I spending enough time working 9-5 on my PhD or will it require more? Academic Guidance 4
Must time require particle interaction (including decay)? High Energy, Nuclear, Particle Physics 4
FTL: Does time even matter? General Physics 40