Reducing matter density would 'inflate' space-time?

[Widdekind]

If mass, embedded in space-time, were to be found to 'decay', and actually 'disappear' from space-time, thereby reducing spatial mass density, down towards the Critical Value, would that "balloon-inflate" space-time? If such a 'vanishing act' were to occur gradually, over cosmic time, would the "balloon" of space-time "just keep inflating", progressively "pushing back" & "procrastinating" the Big Crunch?? Could such a "matter decay" process be construed as consistent, with the claims that the expansion of spacetime is accelerating???

 

Would it be feasible, to solve the Friedman equations, for a spatial matter density, that not only decreased as a(t)^-3, but also included this "radioactive decay" like effect, "over & above" the expansion-based density drop?? What would happen, if the space mass density were to decrease to criticality -- would spacetime "rip open" ??

 

Edited January 27, 2011 by Widdekind

[ajb]

Would it be feasible, to solve the Friedman equations, for a spatial matter density, that not only decreased as a(t)^-3, but also included this "radioactive decay" like effect, "over & above" the expansion-based density drop??

 

 

You can solve the Friedman equations for any mass density and pressure. You need some "equation of state" relating the two. If this is a power law then I think it is very easy to solve.

 

Have a look at the Wikipedia entry on equations of state. It should help you.

 

Now, you have to ask what sort of fluid would have this decay effect? It sounds to me to be very unphysical.

[Equilibrium]

If mass, embedded in space-time, were to be found to 'decay', and actually 'disappear' from space-time

I'm not exactly an expert in this, but how can mass disappear? The Law of Conservation states that energy cannot be created nor destroyed, and the equation E=mc^2 says that matter and energy is interchangeable (meaning that matter is really energy) .

So what I'm trying to say is that matter cannot disappear, and thus this is impossible.

(correct me if I'm wrong I'm only a kid)

[ajb]

I'm not exactly an expert in this, but how can mass disappear? The Law of Conservation states that energy cannot be created nor destroyed, and the equation E=mc^2 says that matter http://www.scienceforums.net/index.php?app=forums&module=post&section=post&do=reply_post&f=7&t=54389&qpid=586612and energy is interchangeable (meaning that matter is really energy) .

So what I'm trying to say is that matter cannot disappear, and thus this is impossible.

(correct me if I'm wrong I'm only a kid)

 

This is certainly true locally in general relativity. So, I would expect a universe that has a violation of the local conservation of energy not to be governed by general relativity.

 

So indeed, you would have to question the validity of the Friedmann equations in describing the expansion of such a universe. These equations are derived from general relativity. Allowing a decay or production of mass would give you something that is inconsistent and difficult to interpret. The whole thing is going to be very unphysical. Maybe you could rescue this by considering very small violations of local energy conservation as a perturbation and consider general relativity as an approximate theory of classical gravity?

 

But this does not necessarily mean the idea is completely daft from the start. The FRW cosmologies are quite independent of general relativity. It is only when deriving the dynamics does one need to invoke general relativity.

 

Such considerations went into the steady state theory. However this is not really supported by the evidence gathered though observation. So the initial idea of the OP seems a bit like a mix if the steady state (in reverse) and the big bang!

 

So the big question is "If not general relativity, then what?"

[Widdekind]

(thanks for the replies)

 

What about the apparent violation, of global (pan-cosmic), energy conservation, w/ photons, whose energy dependence decays, per theory, as a(t)^-4 ?

Edited April 12, 2011 by Widdekind

[csmyth3025]

(thanks for the replies)

 

What about the apparent violation, of global (pan-cosmic), energy conservation, w/ photons, whose energy dependence decays, per theory, as a(t)^-4 ?

Regarding your immediate question, as I understand it the energy "decay" of photons due to the expansion of space is not a loss of energy globally, but rather the simple relationship that energy density/pressure is inversely proportional to volume. I'm not an expert on cosmology, so if I'm mistaken please feel free to correct me.

 

Regarding your original post, the kind of universe your describing (with little or no mass) is, I believe, called a de Sitter universe:

 

A de Sitter universe is a cosmological solution to Einstein's field equations of General Relativity which is named after Willem de Sitter. It models the universe as spatially flat and neglects ordinary matter, so the dynamics of the universe are dominated by the cosmological constant, thought to correspond to dark energy in our universe or the inflaton field in the early universe. According to the models of inflation and current observations of the accelerating universe, the concordance models of physical cosmology are converging on a consistent model where our universe was best described as a de Sitter universe at about a time t = 10 ^{− 33} seconds after the fiducial Big Bang singularity, and far into the future.

(ref. http://en.wikipedia....Sitter_universe )

 

Chris

 

Edited to add the word "globally"

Edited April 12, 2011 by csmyth3025

[lemur]

If mass, embedded in space-time, were to be found to 'decay', and actually 'disappear' from space-time,

I don't think this is as far-fetched as people are making it seem in this thread. I find it fascinating that elements heavier than iron decay spontaneously into lighter elements and that there is a pattern of half-life shortening as elements get heavier. This pattern leads me to wonder what external factors are involved with weak nuclear stability. In other words, I wonder if there are are conditions under which heavier elements become more stable or lighter elements spontaneously fragment into even lighter ones. The latter would consume energy, but I think our physical assumptions may be skewed due to the fact that our point of view is oriented toward a certain consistency of matter-energy instead of, say, inside a star where energy is extremely abundant and matter is in constant flux as a result.

Edited April 12, 2011 by lemur

[csmyth3025]

I don't think this is as far-fetched as people are making it seem in this thread. I find it fascinating that elements heavier than iron decay spontaneously into lighter elements and that there is a pattern of half-life shortening as elements get heavier...

Although there are many isotopes of elements heavier than iron that decay spontaneously, there are also many that are not thought to be subject to spontaneous decay (even theoretically). I believe the heaviest of these is Zr₉₂.There are an additional 55 heavier elements (up to atomic number 164) that are thought to spontaneously decay in theory but have never been observed to do so.

(ref. http://en.wikipedia....observed_decays )

 

Chris

[Widdekind]

Although there are many isotopes of elements heavier than iron that decay spontaneously, there are also many that are not thought to be subject to spontaneous decay (even theoretically). I believe the heaviest of these is Zr₉₂.There are an additional 55 heavier elements (up to atomic number 164) that are thought to spontaneously decay in theory but have never been observed to do so.

(ref. http://en.wikipedia....observed_decays )

 

Chris

 

 

Would that be at absolute zero temperature? With thermal oscillations, in the nucleus, and more binding energy-per-nucleon available, w/ an iron structure, would such a decay occur, given astronomical time scales?

[csmyth3025]

Would that be at absolute zero temperature? With thermal oscillations, in the nucleus, and more binding energy-per-nucleon available, w/ an iron structure, would such a decay occur, given astronomical time scales?

As far as I know, temperature has no effect on the half-life of nuclei that sponataneously fission and will not make a nucleus that has no tendency to fission aquire such a tendency.

 

Chris

[Widdekind]

What would happen, if our cosmos was critical, according to current matter density... when you factored in, the contribution of photons? Photons "mysteriously lose mass-energy density", during spacetime expansion, yes?

[Airbrush]

I'm not exactly an expert in this, but how can mass disappear? The Law of Conservation states that energy cannot be created nor destroyed, and the equation E=mc^2 says that matter and energy is interchangeable (meaning that matter is really energy) .

So what I'm trying to say is that matter cannot disappear, and thus this is impossible.

(correct me if I'm wrong I'm only a kid)

 

If or when protons decay there would be a flash of energy released. So matter is not destroyed only converted into energy and maybe some other lighter particles. But protons are supposed to have a very long life, so maybe the universe is not old enough yet for any protons to decay.

 

"The spontaneous decay of free protons has never been observed, and the proton is therefore considered a stable particle. However, some grand unified theories of particle physics predict that proton decay should take place with lifetimes of the order of 10 to the 36th power years, and experimental searches have established lower bounds on the mean lifetime of the proton for various assumed decay products.

 

"Experiments at the Super-Kamiokande detector in Japan gave lower limits for proton mean lifetime of 6.6 x 10^33 yr for decay to an antimuon and a neutral pion, and 8.2 x 10^33 yr for decay to a positron and a neutral pion."

 

http://en.wikipedia.org/wiki/Proton#Stability

Edited June 2, 2011 by Airbrush

[DrRocket]

If mass, embedded in space-time, were to be found to 'decay', and actually 'disappear' from space-time, thereby reducing spatial mass density, down towards the Critical Value, would that "balloon-inflate" space-time? If such a 'vanishing act' were to occur gradually, over cosmic time, would the "balloon" of space-time "just keep inflating", progressively "pushing back" & "procrastinating" the Big Crunch?? Could such a "matter decay" process be construed as consistent, with the claims that the expansion of spacetime is accelerating???

 

Would it be feasible, to solve the Friedman equations, for a spatial matter density, that not only decreased as a(t)^-3, but also included this "radioactive decay" like effect, "over & above" the expansion-based density drop?? What would happen, if the space mass density were to decrease to criticality -- would spacetime "rip open" ??

 

 

All the preceeding replies notwithstanding, decay doesn't do much for the picture.

 

Assuming that you have not tossed general relativity out the door, energy as well as matter, is included in the stress-energy tensor that determines gravitation. So unless not only the matter, but also the energy that is associated with decay "disappears", gravity marches on. If both the matter and energy disappear, you have a local violation of general relativity. That would be a big deal indeede.

 

If general relativity is off the table, then we are back to ajb's question, "What replaces GR ?"

Edited June 2, 2011 by DrRocket

[Airbrush]

All the preceeding replies notwithstanding, decay doesn't do much for the picture.

 

Assuming that you have not tossed general relativity out the door, energy as well as matter, is included in the stress-energy tensor that determines gravitation. So unless not only the matter, but also the energy that is associated with decay "disappears", gravity marches on.

 

So what you are saying is that even if matter decays into other particles and releases some energy, the energy released retains a gravitational effect? Suppose a galaxy could be converted 100% into energy. The energy will continue to pull on neighboring galaxies?

[lemur]

What if mass is relative the way spacetime dilation causes the yardstick to shrink or expand for length contraction? Could it be that while mass is measured as constant, it is actually changing in different gravitational situations and its stability could ultimately give way as a result, e.g. less radioactive atoms becoming radioactive with half-lives shortening, etc.? Is this along the lines of what this thread is contemplating?

[J.C.MacSwell]

So what you are saying is that even if matter decays into other particles and releases some energy, the energy released retains a gravitational effect? Suppose a galaxy could be converted 100% into energy. The energy will continue to pull on neighboring galaxies?

 

Basically yes. In fact if you had a "containment shell" around it that would not allow any energy (say photons) to escape, it would be indistinguishable from mass with the same containment. That would effectively still be it's mass.