# Alan Guth, Gravitationally repulsive material?

1. Jan 9, 2014

### Herbascious J

Does anyone have any resources which explain the nature of Alan Guth's 'gravitationally repulsive material'? I would like to understand a basic explanation of how this material becomes a negative pressure at extremely high temperatures. I understand that this arises from GR and the standard model of particle physics some how. Is it like another state of matter beyond plasma??

2. Jan 9, 2014

### Chronos

This gravitationally repulsive state was suggested by Guth as a part of inflation. His idea is the very early universe contained a region imbued with repulsive gravity - a condition theoretically possible under GR and particle physics. This repulsive gravity provided the kick necessary to initiate inflation causing the universe to double in size every ~10E-37 seconds. It requires enormous energies, far beyond any we can probe experimentally today. The state of matter under these conditions is unlike any we are familiar with. It was still far too hot for leptons [electrons, neutrons, protons] to form, which did not occur until the universe was about 10E-8 seconds old. It was too even too hot for quark to exist until the universe was about 10E-35 seconds. Inflation ended around 10E-32 seconds, so the only 'massive' particles that could exist at that time were quarks.

3. Jan 9, 2014

### Herbascious J

Hi and thank you for the detailed information. I'm looking for a further description of "a condition theoretically possible under GR and particle physics". I would like to know why such high energies create negative pressure (and repulsive gravity) in matter. Is there some basic principle within particle theory that suggests negative pressure at high energies for matter?? Any input is appreciated.

4. Jan 9, 2014

### M. Bachmeier

Dark Matter... Dark Energy...

5. Jan 9, 2014

### Staff: Mentor

Can you explain why they should be relevant (and in case of dark matter, why repulsing) at very high energy densities?

6. Jan 9, 2014

### bapowell

It has nothing to do with "high energy" and it does not happen for just any kind of matter -- it is a special kind of energy, namely an energy density with quantum numbers of the vacuum (usually referred to as "vacuum energy"). Vacuum energy is a very unusual kind of thing; for one, it has a constant density. This means that it does not dilute as the universe expands -- it is persistent. It is *this* property that results in a negative pressure. High densities of vacuum energy are believed responsible for the early bout of ultrarapid expansion called inflation; in much, much lower densities it might also be implicated in the present-day accelerated expansion of the universe.

7. Jan 9, 2014

### M. Bachmeier

I would have to make assumptions, without evidence.

But I believe the standard model has yet to fully demonstrate a complete and stable standard.

Newtons equations were considered solid and without question for many years.

8. Jan 9, 2014

### Chronos

Affirming bapowell, current vacuum energy may be remnants of the original scalar field responsible for inflation. It was too feeble to become noticeable until several billion years ago. @M Bachmeier, you would be well advised not to indulge in such discussions based solely on 'instinct'. You will notice contributors here regularly offer references to published papers in support.

9. Jan 10, 2014

### Chalnoth

Just to be clear, while this is definitely a line of thought that many theorists have considered to be quite enticing, nobody has yet come up with a specific idea that is really compelling. There are multiple ideas for how this could be, but they tend to be rather ad-hoc.

Usually this kind of idea takes the form of a scalar field that causes inflation, and when inflation ends the field doesn't go away entirely. Instead it "tracks" the matter density for a while, until, at some sufficiently-low density, it "freezes out" and stops changing its value, effectively becoming a cosmological constant.

10. Jan 10, 2014

### Herbascious J

At what point is matter introduced? Shouldn't there be some kind of matter like energy during inflation that will decay into particles?

11. Jan 11, 2014

### bapowell

Inflation comes to end when the inflaton field finds itself in the vacuum. The field retains some potential energy even in the vacuum, which it dissipates by oscillating about the minimum of the potential (sort of like water sloshing about in a bucket). These oscillations manifest themselves as inflaton particles which subsequently decay into hot radiation, effectively resulting in a hot big bang from which conventional, post-inflationary expansion picks up.

12. Jan 14, 2014

### Naty1

Generally seems to be no consensus understanding of precisely what drove expansion. The 'gravitationally repulsive material' as has been noted is conjectured to be a state of vacuum energy.

I attempted to initiate a discussion of a related theory but it did not go as far as i had hoped:

Can torsion avoid the big bang singularity

In a nutshell:
wikipedia:
Somewhere I read that including torsion makes the stress energy momentum tensor non symmetric.....Including torsion is what appears to be the source of the high density repulsion.

In the Road to Reality, Roger Penrose notes an insight into the effects of including torsion: Apparently the amount of torsion affects the closing of a parallelogram of geodesic edges about a point. He says going in two opposite directions around the parallelogram yields two different points of closure resulting from the presence of torsion.

I'll see if I can find that in his book.

edit: Inflation has some 70+ or so variations. One listing is in "The future of Theoretical Physics and Cosmology" provided by Paul Shellard at Steven Hawkings 60th birthday celebration...Pg 764.

Last edited: Jan 14, 2014
13. Jan 14, 2014

### Naty1

Herbascious J:

If you plow through portions of Roger Penrose THE ROAD TO REALITY he has some interesting but commentary....[maybe worth a library read, but not a purchase for the current subject.]

here are a few comments, in no particular order:

Note 19.10:
and he lists on page 470 half a dozen references.....

Page 746: Penrose raises this issue in the chapter SEPECULATIVE THEORIES OF THE EARLY UNIVERSE:

Also,

http://en.wikipedia.org/wiki/Einstein-Cartan-Sciama-Kibble_theory
[I think this is improperly stated.. seems like it should be 'torsion of spacetime'.....

Even Penrose mentioned the difficulties of the math....primes on super and subscripts.....and on and on....

If anone has any insights why spin and curvature might link to form repulsive gravity that would be great. For example, does spin force curvature to 'unwind'? And I can't imagine 'particle' spin....spacetime torsion, ok.

14. Jan 14, 2014

### Chalnoth

He's basically wrong about inflation. It is typically thought that the inflaton is not some entirely new field, but instead one of the menagerie of scalar fields which are likely to exist in any grand unified theory.

In essence, it's almost impossible to produce a grand unified theory that doesn't also happen to have a number of scalar fields in it. All that is required is for one of them to have the right properties to become the inflaton. This is a markedly lower barrier to cross than the one supposed by Penrose.

15. Jan 14, 2014

### Herbascious J

I have a question; It seems Guth is saying that energy from this inflation scalar field decays into particles. If it was possible to recreate sufficiently high energies (I realize it's not), could we convert matter back into 'inflatons'?

16. Jan 14, 2014

### Chalnoth

Yes, absolutely. Even if we could build a particle accelerator capable of such a feat, however, it would be much much harder to actually produce inflation: inflation doesn't just require inflatons, it also requires that the value of the inflaton field be nearly constant and of an appropriate value across a region of space (a very small region of space, but not a single point either).

17. Jan 14, 2014

### Naty1

18. Jan 14, 2014

### Chalnoth

Quantum gravity isn't necessary. If the inflaton field exists, then inflatons can be produced in sufficiently high-energy collisions, full-stop. This must necessarily be the case, because if it weren't, then inflatons could not decay into standard model particles. Which they had to to produce our universe.

19. Jan 15, 2014

### Naty1

Chalnoth:
What does "full stop" mean?

20. Jan 15, 2014

### Chalnoth

As in you don't need to know anything more about the inflaton field to know it can be produced in a particle accelerator than the fact that inflation ended, and the end of inflation produced standard model particles.

21. Jan 15, 2014

### Herbascious J

There is a line of thought that has hung me up on all of this. Perhaps my understanding is off. I believe that particles carry with them aspects like charge, spin, lepton number, baryon number, and even mass, etc. To me this is what distinguishes matter from other forms of energy. Although these attributes can be annihilated (anti-particle collisions) and reduced to pure energy, it seems that any field that gives rise to matter, should in some aspect contain these attributes in some form. Otherwise, shouldn't the energy of the inflation field simply decay into photon radiation? I apologize for my ignorance here, I'm stepping well out of my current grasp of things.

P.S. - I guess I'm arguing that this field should represent a high energy form of matter. I guess if matter can be reduced to pure photon energy then then reverse must be true and what ever the nature of the inflation field, the energy from it can become particles when released. Fascinating theories, but immensely counter intuitive :)

Last edited: Jan 15, 2014
22. Jan 15, 2014

### Chalnoth

Right. This is what normally happens when we produce massive particles in particle accelerators: they decay. We mostly know about them from their decay products. The recent Higgs detection, for instance, stems from combinations of outgoing particles (typically muons and photons) whose combined energies are around 125GeV.

Many of these more massive particles have decay times of $10^{-10}$ seconds or less (I'm not sure we yet have a handle on the decay time of the Higgs, but I'm sure it's tiny).

If the inflaton couldn't decay into other particles, it would still be around in large numbers.

23. Jan 15, 2014

### Naty1

Sounds good. That is how particles register. How we observe them. It is what they ARE. In the string theory view, different vibrational energies and patterns, analogoues to different resonant frequencies for example, underly those observed characteristics.

also sounds ok ....I think it is Leonard Susskind that mentions there are something on the order of [don't quote me here on the exponent, but it's huge] 1018 photons for every matter particle.

So if matter particles can transform to energy and energy can transform to matter, seems reasonable that attributes of each somehow reside within. In fact that's kind of what a grand unified theory does: unites strong,weak,electromagnetic and gravity into a single high energy entity. Everything in the universe originated from that initial high energy [bang] state.

On the other hand, as I understand things, the [matter] elements directly from the bang were hydrogen,helium lithium....lighter stuff.....I believe the proportions of those can be predicted quite accurately via existing theory. More elements originate from stars [fusion] that formed billions of years later and still more different from supernovas.

see 'nucleosynthesis' for more.

24. Jan 15, 2014

### Herbascious J

Ok, so (according to theory) the inflaton decays into the particles we observe. Does this make the inflaton a form of matter (unlike a photon)?

25. Jan 15, 2014

### Chalnoth

Quantum mechanically, a photon isn't really that distinct from other forms of matter, except for the fact that it has no mass. It's just one (of many) quantum-mechanical fields. It doesn't form solid objects because of the lack of charge and mass, but then neutrinos don't form solid objects either.

In some ways, an inflaton would be a bit more like a photon than, say, an electron, because it would be a boson (electrons, protons, and neutrons are all fermions). Though I suppose the particle it has most in common is the Higgs, as the Higgs is not only a boson, but is a scalar boson and also has mass.