Universe with only e+ , e- , photons, and gravitation?

In summary: I'm not sure how much more "flexible" string theory could be, but I guess it's theoretically possible. If so, it would be easier to solve since we would only have to solve the equations for the particles in the toy model rather then the full theory.
  • #1
Spinnor
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Universe with only "e+", "e-", photons, and gravitation?

In theory could we have a universe with only electrically charged spin 1/2 particles and antiparticles of mass m and electrical charge e and that interacted only gravitationally and electromagnetically?

If so could we fine tune things so that such a universe was long lived and closed?

In the early phase of such a universe would there be roughly twice the energy density in the fields of the charged particles as in the electromagnetic field?

Thanks for any help!
 
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  • #2


maybe this is a bit linked to my thread "what is strong gravity". but what is your idea.
 
  • #3


qsa said:
maybe this is a bit linked to my thread "what is strong gravity". but what is your idea.

I'm thinking (I hope %^) that the answer to my first question is yes. If we get some deeper "Theory of Everything" then I'm guessing the answer to my first question might go either way.
 
  • #4


Odd questions... Certainly you could write down a Lagrangian for quantum electrodynamics (with just one species of particle, as you describe) coupled to gravity, and you could calculate what this Lagrangian predicts in certain limits. You could also figure out the cosmology for such a universe, by imitating all the calculations performed in conventional cosmology, e.g. thermodynamics of the early universe. But your fictitious universe will be a lot simpler than the real one, e.g. it contains no atoms.
 
  • #5


We would still have positronium %^)

And if we made the mass m greater and e smaller then positronium might last long enough for more complicated temporary "atoms"? Under the right conditions two positively charged particles might be temporarily bound to two negatively charged anti-particles?

Thanks for your replies!
 
  • #6


Even standerd physics says only electrons exist. Protons are composites. But no agreed on confinment theory exists as far as i know. Almost all others have short life and are produced as part of interaction.
 
  • #7


mitchell porter said:
Odd questions... Certainly you could write down a Lagrangian for quantum electrodynamics (with just one species of particle, as you describe) coupled to gravity, and you could calculate what this Lagrangian predicts in certain limits. You could also figure out the cosmology for such a universe, by imitating all the calculations performed in conventional cosmology, e.g. thermodynamics of the early universe. But your fictitious universe will be a lot simpler than the real one, e.g. it contains no atoms.

So I will take that as a yes, thank you %^)

The follow up question relates to String Theory. Is String Theory "flexible" enough so that it could also include such a simple universe? If so wouldn't such a toy model be easier to solve then trying include all fields?

Thanks for any help!
 
  • #8


http://arxiv.org/abs/hep-th/0403247 contains a string theory model for quantum electrodynamics in four dimensions. It's Type IIB string theory with a space-filling D9-brane and another space-filling anti-D9-brane, and then you have a "probe" D3-brane interacting with that background. See table 2 and the bottom of page 5 for where the photon and electron come from.
 

1. What is the main difference between this universe and our current one?

The main difference is the absence of matter in the form of protons and neutrons. This means that there are no atoms or elements, and therefore no solid objects or living organisms. The only particles present are electrons, positrons (anti-electrons), and photons.

2. How does gravity work in this universe?

Gravity still exists in this universe and is the dominant force between particles. It is responsible for the attraction between opposite charges (electrons and positrons). However, without the presence of protons and neutrons, there is no gravitational pull between massive objects such as planets and stars.

3. Can life exist in this universe?

It is unlikely that life can exist in this universe as we know it. Living organisms require a complex structure of atoms and molecules, which are absent in this universe. Without these building blocks, it is difficult to imagine the existence of living beings.

4. How does the absence of matter affect the expansion of the universe?

The absence of matter means that there is no significant mass to slow down the expansion of the universe. Therefore, the universe in this scenario would continue to expand at an accelerated rate, driven by the energy of the particles present.

5. What would the universe look like in this scenario?

Without the presence of matter, the universe would be mostly empty and dark, with only particles and photons scattered throughout. There would be no stars, galaxies, or other structures commonly seen in our universe. The only sources of light would be from annihilation events between particles and from the cosmic microwave background radiation.

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