Defiant Heretic

A few days ago, I was thinking about how the matter in the universe will probably break down into its component particles, and eventually energy. I then wondered if it might be converted back to matter eventually for some reason, and if so, if this might have been what happened in the big bang.

If matter was not initially packed into a singularity, but instead scattered across the universe, is it possible that the big bang was actually energy converting into matter on a large scale, and the expansion of the universe is caused entirely by dark energy/cosmological constant?

(I don’t know if this is a valid theory, but I don’t see any glaring contradictions with what I know so far.)

elwoodblues

I'm not sure quite what you're saying here. Sounds rather like a cyclical universe, which has been kicked around physics circles for a long time. Big Bang, expanding universe, then gravity pulls it back in, eventually resulting in another Big Bang.

The decomposition of matter into energy is basically accepted as well. It just takes a long, LONG time for some particles to do it. As I understand it, it's entropy, so energy doesn't spontaneously 'compose' back into energy (not without good reason, anyway).

I could be wrong, though. It's been awhile since I've poked my nose into that corner of science. Been focusing on evolutionary biology and logic theory for the most part.

Oxymoron

Models of the universe are generally developed by the posing and solution of the Einstein field equations. It's hard to tell if your model is a valid solution of said equations, but its validity may depend on its being so.

crocodile deathroll

Here is a website that specializes on the area if you are interested. They even have an open forum
<a href="http://www.superstringtheory.com/experm/index.html" target="_blank">The Official String Theory Website </a>

Defiant Heretic

Well, it would be cyclical, but in the sense of state, not position. The particles would cycle between matter and energy, but might continue expanding instead of re-collapsing, depending on how gravity and the cosmological constant affect pure energy.
Yes, I didn't mean that matter would become energy spontaneously, just that it would decay eventually. I don't know whether the energy would convert to matter quickly or not. I'm basically asking if it would be able to convert to matter at all.

Gauge Boson

Unless something completely unexpected happens and the cosmological constant reverses itself or stops very soon (in cosmological time), this is highly unlikely. Of course, if the universe cycles, expanding then collapsing to a relatively small size, such a scenario is possible, though improbable. The only way I know of that massless particles can produce massive particles is through pair-production. That is, they must collide, annihilating eachother and producing a particle-antiparticle pair with the same energy and momentum.
A small problem with your hypothesis is that it makes a distiction between matter and energy; there is none. Matter is simply a form of energy. Massless particles (which I surmise would fall into your energy category) are no diferent from massive particles (except that they are unaffected by the Higgs field if it exists). They have momentum, they are affected by gravity, and they act gravitationally on other 'stuff'. They have no rest energy, but that doesn't matter because they always travel at the speed of light. If the cosmological 'constant' continues at its present value (a conservative assumption because Quintessence predicts that it may get larger), the universe will expand ever-faster. Here is a brief future history of the universe with a constant cosmological 'constant' (1). Times are given in years from now.
5x10^9: the Sun dies
7x10^11: the universe cools to the Gibbons-Hawking temperature (the lowest possible temperature due to vacuum energy)
5x10^12: contact is lost with everything beyond our cluster of galaxies - they receed faster than light
10^14: star formation ends
10^15: expansion causes planets to leave their parent stars
10^30: black holes consume the vast majority of matter in galaxies
10^37: galactic fuel exhausted at current rate of consumption (but stars died long ago)
10^65: quantum tunneling 'liquifies' matter (it decays into elementary) particles
10^85: the few electrons and positrons close enough together bind into a new kind of matter
10^98: the last black holes evaporate

Remember that as the universe expands, the deceleration parameter decreases (2, 3) due to decreasing energy density (dark energy is always of uniform density (2) ). It is already negative (2, 4, 6), so this will mean that the universe, even with a constant cosmological 'constant', will expand faster and faster.

Of course, we don't know the details of dark energy yet. But it is almost certain that it comes from vacuum energy. This energy is always gravitationally repulsive (2, 4, 5), so I am unaware of any mechanism that could cause it to reverse short of a drastic change in the laws of physics. According to Jeremiah Ostriker and Paul Steinhardt, Quintessence (a variable cosmological 'constant' that causes slightly slower cosmological acceleration than a true cosmological constant) may cause the acceleration to increase, remain constant, decrease, or switch off, but cannot reverse itself (2). Both the cosmological constant and Quintessence theories preclude a collapse.

(1) "The Fate of Life in the Universe", Scientific American, vol. 12, no. 2: Cosmology special issue. Krauss, Lawrence M. and Starkman, Glenn D.
(2) "The Quintessential Universe", Scientific American, vol. 12, no. 2: Cosmology special issue. Ostriker, Jeremiah P. and Steinhardt, Paul J.
(3) Universe, Fifth Edition. Kaufmann, William J. III and Freedman, Roger A. W.H. Freeman & Co., New York, 1999.
(4) "Cosmological Antigravity", Scientific American, vol. 12, no. 2: Cosmology special issue.
(5) University Physics with Modern Physics, 10th Edition. Young, Hugh D.; Freedman, Roger A.; Sandin, T.R.; Ford, A. Lewis. Addison-Wesley-Longman, 2000.
(6) "Why Cosmologists Believe the Universe is Accelerating." Turner, Michael S. <a href="http://www.arxiv.org/abs/astro-ph/9904049" target="_blank">Available online at the arXiv e-print archive</a>.

[ November 17, 2002: Message edited by: Gauge Boson ]

[ November 17, 2002: Message edited by: Gauge Boson ]

[ November 20, 2002: Message edited by: Gauge Boson ]</p>

Defiant Heretic

So you're basically saying that massless particles, e.g. energy, could only be transformed into massive particles, e.g. matter, if they were in close proximity to each other, and since dark energy exerts a greater influence than gravity, the universe will be unlikely to attain a high enough density for this to occur. Is this an accurate summary?

By the way, even though it looks like my hypothesis is wrong, I’d still like to clarify a few points.

• I realize that matter and energy are essentially the same thing. I meant energy would change into matter in the same sense that water vapor changes into ice.
• The point at which I had matter turning into energy would probably be right after 10^98: the last black holes evaporate.

Gauge Boson

Essentially, yes. Except that the force exerted by dark energy is gravity and the massless particles must actually collide (though "collide" has a slighly different meaning in quantum mechanics because particles only have equivalent cross-sectional areas).

We wouldn't know anything if nobody ever proposed a hypothesis that later turned out wrong (though yours is just very unlikely). If the cosmological 'constant' remains constant, at 10^98 years from now the universe would be expanding very fast, perhaps faster than during inflation (I'll have to look up the current value of the deceleration parameter for a back-of-the-envelope calculation). The particles evaporating from the black hole would be pulled apart too fast to ever collide. It could eventually be so fast that the 'virtual' particles that probably provide the dark energy could be pulled apart faster than they could annihilate, analogous to how black holes evaporate (one way of thinking of black hole evaporation is that 'virtual' pairs near the event horizon can lose a particle into the black hole, though there are other, mathematically equivalent conceptualizations). If, OTOH, quintessence ended abruptly at, say, 10^20 years from now, the expansion would still accelerate too fast due to the low, decreasing density and already-rapid expansion.

It is worth noting, however, that a couple of decades ago dark energy was never thought of, except when quoting Eistein saying that the cosmological constant was his "biggest blunder" (he invented it to make the universe static and eternal by perfectly countering the gravitational pull of energy in the universe). So it is still possible that we might someday discover an unknown mechanism that could cause partial recollapse, though obviously unlikely. Unless the laws of physics drastically change, however, the recollapse would need to be to the point that the universe would no longer be a statistical system. This is because the laws of thermodynamics (in this case, the second law) only apply to statistical systems. Without this, entropy would remain high, possibly at its maximum (the "heat death", though a cosmological constant prevents this if the expansion reaches a high enough speed).

This leads us to another question: would the universe itself have to recollapse, or only the particles in it? Only the 'stuff', because only the observable universe matters. This might have a different effect on the resulting universe, though, if spacetime exists independently of 'stuff' (we really don't know the answer to that one yet ).

BTW, I'm glad to see someone asking tough questions. Thanks.

lpetrich

That must be a typo -- the Sun will become a Red Giant about 5-7 billion years (10^9) from now, and will become a white dwarf and slowly cool off afterwards.

Kharakov

I thought electrons and positrons annihilate eachother to form photons (high energy- gamma).