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Q & A: origins of dark energy?

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Most recent answer: 11/27/2011
Q:
I understand that energy can only transform into matter in a particle accelerater(ie. a tiny big bang),so could the loss of energy from the supposed spark of life explain the concept of dark energy.
- nick collins (age 48)
bexhill, east sussex, england
A:
A couple of points there are a little hard to follow. By transforming energy into matter, I think you mean photon collisions giving matter-antimatter pairs. It's true that such processes must have been common in the earliest stages of the big bang, when there was a high density of high-energy photons.  I have no clue what "the spark of life" refers to. Even Google wasn't much help, turning up references to some tv series.

So what sorts of things are suspected as possible origins for the dark energy that's usually believed to give the acceleration of the cosmic expansion? In general, the sorts of interactions we see between particles are leftovers from some much more general set, frozen into a particular state. One version of this idea (string theory) allows for some very large number of possible background states, differing in the ways that extra dimensions are curled up on a tiny scale. Each of these background states has its own energy density. In this picture, the dark energy density would just come from the accident of which background state had formed in our universe. Needless to say, at this point there's an element of speculation involved.

Mike W.

(published on 06/16/2011)

Follow-Up #1: the spirit of dark energy

Q:
the spark of life means your soul or spirt or concious
- nick (age collins)
bexhill, east sussex, england
A:
I'm not sure how those phenomena are supposed to connect to the universe-wide accelerating expansion.

Mike W.

(published on 06/22/2011)

Follow-Up #2: living energy

Q:
If a human body has energy in the form of electricity firing between neurons in our brain or flexing muscles in our heart or arms and legs, then where does this energy go too when we die. When a body dies it’s matter decays and is returned too the earth to be recycled. Decaying human body --> soil nutrients --> grass --> cow --> living human body. Energy cannot recycle in this way; it must therefore go somewhere else. Someone (don’t know their name) did an experiment (don’t know what it was called) on a dying human, that weighed them, before and after their death, and found a loss in mass (don’t know how much - not much), but was not bodily fluids or gases, so they believed it could only be the conscience or the soul. This does not mean I believe in an afterlife or a god This thought brings us to my theory. Electrical energy --> consciousness/spirit/soul (*)--> death --> floating in the atmosphere (*) --> dissipation from the top of the atmosphere, by the solar winds (more energy and matter) into the cosmos, as Dark Energy. This could also be applied to matter as volcanic dust and water vapor --> solar winds --> Dark Matter. It could explain the decrease over eons in the size and mass of the earth. Indeed on a universal scale it might explain how all energy and matter, both organic and stellar can transform into Dark Matter and Dark Energy. Increasing the overall mass of the Universe and therefore increasing its expansion at an exponential rate. (*) I realize and except these points are very open to personal belief and interpretation, but its only a theory.
- nick (age collins)
bexhill, eas sussex, england
A:
First, I should make clear that here we use "energy" only in the well-defined physical sense, with just that single meaning, and never in some other metaphorical sense. Of course there's some energy associated with being alive. We're warmer than our environment, usually, so there's some miscellaneous thermal energy. There are those little bits of electrical energy in nerve currents. There's quite a bit of energy available in our chemistry, which is way out of equilibrium with the oxygen-containing atmosphere.  Nothing interesting happens to that energy after death. The speck of electrical energy almost instantly reverts to heat. The heat trickles out into the environment. The chemicals gradually react with each other and the atmosphere to approach equilibrium, releasing more heat.

Mike W.

(published on 06/24/2011)

Follow-Up #3: dark energy

Q:
Well, apparently there is "dark energy," now that it's been officially blessed by the Swedish Academy of Sciences. Let's take as axiomatic that everything that happens in this universe has a cause which is in this universe. You may consider this to be tautological based on the definition of "universe." You're obviously a materialist. What is the material source of this officially sanctioned "dark energy?"
- mark (age 55)
ca, usa
A:
You're referring to the recent Nobel prize for measuring the accelerating expansion of the universe. Given the dynamics of General Relativity, one obvious way to account for that acceleration would be if the vacuum fields were to have some positive energy density. We've mentioned some possible candidates for the sources of such an energy density above. The mystery, in the current framework, is not why there's some such energy density but why it isn't much, much larger, as one would get from a naive calculation using standard quantum mechanics. It is also possible, however, that some other physical effect is responsible for the accelerating expansion, so one should not as yet say for sure that dark energy as such has been confirmed.

Mike W.

(published on 10/29/2011)

Follow-Up #4: pressure in General Relativity

Q:
nope, sorry. A positive energy density leads to an increase in the universe's T_{mu nu}, and slows the contraction. Due to the m^2 term in QED a negative energy density would have the same effect. you're going to have to do better than that.
- mark (age 55)
ca, usa
A:
I believe you've dropped the pressure term. If the energy density is fixed and positive, that gives a negative pressure (-dU/dV). It counts 3 times more as negative pressure than it does as positive density. It's not my area, but I believe this is a nice standard description:

Mike W.

This is an unchecked post, since Lee is currently in Paris.

(published on 11/27/2011)

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