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#1
Sep504, 01:43 PM

P: 146

Can a volume of space exist without the presents of some form of energy?



#2
Sep504, 02:36 PM

PF Gold
P: 7,363

It has been experimentally shown that "empty" space is a seething sea of particleantiparticle pairs that arise and selfannihilate. These virtual particles have opposite spins, charges, and timelines, but each of the members has MASS. There is therefore a baseline amount of mass populating every speck of "empty space". This ground state is called Zero Point Energy.
If you do a Google search on "Casimir Effect", you will find lots of interesting links, including explanations of how ZPE has been experimentally verified. 


#3
Sep504, 03:28 PM

P: 146

I assume this idea is widely accepted in mainstream thinking.



#4
Sep504, 03:38 PM

PF Gold
P: 7,363

Space versus energy



#5
Sep504, 03:53 PM

P: 1,308




#6
Sep504, 04:03 PM

Sci Advisor
PF Gold
P: 9,433

Here is a nice read that is not very technical
http://www.sciam.com/askexpert_quest...mber=1&catID=3 


#7
Sep504, 04:11 PM

PF Gold
P: 7,363




#8
Sep504, 05:23 PM

Sci Advisor
PF Gold
P: 9,433

http://arxiv.org/abs/hepth/9912205 


#9
Sep504, 05:42 PM

P: 1,308




#10
Sep504, 05:56 PM

Sci Advisor
PF Gold
P: 9,433




#11
Sep604, 10:32 AM

P: 1,308

It would seem that all entities of reality of any physical concern are assumed to be describable by some mathematical structure, be it stars, molecules, particles, or even dimensions. All represent some sort of structure, and there should be some sort of entropy or information associated with their form and their dynamics. I'm considering a hypothesis that the universe as a whole conserves entropy/information. Perhaps it is zero to begin with as well. I wonder if starting with this assumption can guide us in understanding (mathematically) how the universe was constructed from scratch (nothing?) I would think that such a starting premise would also be able to account for any superposition of quantum effects (such as in quantum geometry of gravity, etc.) since that premise is so closely linked to probabilities. Any thoughts gentlemen? 


#12
Sep604, 11:02 AM

Emeritus
Sci Advisor
PF Gold
P: 2,021

Plus there's the Cosmic Microwave Background radiation that permeates throughout the universe.



#13
Sep604, 12:03 PM

PF Gold
P: 7,363

Since we know that mass can distort spacetime, I'm prepared to accept elasticity over continuous creation, but I could be wrong about that. It could even be a combination  perhaps there is a limit as to how much these discrete units can be distorted, at which point they break and form two new units.... Pure speculation only, but there will be serious consequences for your entropic model in any event. 


#14
Sep604, 02:45 PM

P: 1,308

Let's see. What would be the classical limit of this "etropic universe"? As I understand it, classic physics is deterministic so that everything happens with a probability of 1. So there is no information added by new events. But what is the link between information and QM? Didn't they do some work on this in regard to black holes? What is the information content of the fundamental quantum mechanical situation where each measurement is a choice from an ensemble? Does the collapse of the wave function represent an increase in information, or decrease of entropy? Does the creation of possible states represent an increase of entropy? Are the two always balanced? Let's see. IIRC, the probability distribution across quantum states is normalized to 1. So there is no information in the existence of the distribution itself. But when the wave function collapses to one choice from the possibilities, there is an increase of information associated with that. Where then is the entropy at least balanced if entropy decreases with a choice from an ensemble. 


#15
Sep604, 07:58 PM

Emeritus
Sci Advisor
PF Gold
P: 4,014

IIRC, it was partly because of these entropy, ZPE, etc thingies that Hawking lost his recent bet!
While I'm sure all those who've posted to thread are clear about what's within the bounds of observationally validated theory and what's not, it may help some readers to have a summary (if this is significantly incorrect, I'm sure folk will amend it):  the Casimir effect is wellestablished, experimentally, and the observations are consistent with theory  'dark energy' or the 'cosmological constant' is ascribed as the cause of the observed acceleration of the expansion of the universe; however, while the observations are now much more clear cut than five years ago, IMHO they are still not as definitive as many portray them. The 'explanation' of the observations as ZPE/cosmological constant/dark energy/whatever is a topic of great energy and excitement among cosmologists; IMHO it's far too soon to say that there's a consensus on this  no region of space is 'pure vaccuum'; not only are there gravitational fields (everywhere, not just near the Earth), but also a very significant neutrino flux (both relict and of more recent origin), the CMBR (as Phobos said; it's everywhere except regions that are opaque to microwaves), and cosmic rays (a hollow sphere deep underground may be relatively free of these; most of the universe is not). None of this is 'theory'; there are good observational results for all (except the relict neutrinos).  anything at all coming from String/M Theory or LQG is pure theory (some would say pure speculation); there are *no* observations or experiments which constrain either theory in any significant way; this includes anything to do with 'stringrelated entropy', or 'discrete fundamental units of spacetime'. 


#16
Sep604, 08:39 PM

PF Gold
P: 7,363

There are experiments in the wings to probe the structure of spacetime using cosmic rays and gamma ray bursts. We will learn something about discretization of spacetime (and its coarseness) either way. String and LQG may be fringe, but if they show any promise in reconciling gravity with the other forces, the scientific community must explore them. 


#17
Sep904, 12:03 PM

P: 1,308

I think this all constitutes a proof that the universe as a whole conserves information, right? 


#18
Sep904, 02:07 PM

PF Gold
P: 7,363

What is the information value of a preSN star? Now what is its information value after it goes SN and blasts its matter all over? To revisit something from earlier in the thread, zero point energy exists as the ground state of "empty" space. Does ZPE have an information value in your U, or do you assign information value only to "real" things (things that are detectable to you because they exist above the ground state)? One last example  a new unshuffled deck of cards may represent a highly entropic state to you because you personally understand the significance of the suits and numbers, but does it really contain more information (in your Universe) than any of the quasirandom states that the deck might end up in after being shuffled? 


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