John15 said:How does the BB theory allow for the creation of matter. Bt this I mean the sub atomic particles that make up atoms i.e. the quarks and electrons. From what I have read it seems to assume that they already pre-existed and condensed out of the fireball to form atoms.
John15 said:How does the BB theory allow for the creation of matter. Bt this I mean the sub atomic particles that make up atoms i.e. the quarks and electrons. From what I have read it seems to assume that they already pre-existed and condensed out of the fireball to form atoms.
Right, but this has nothing necessarily to do with the origin of energy in the universe; after all, these are vacuum fluctuations -- virtual particles. How do you suppose they become real? Now, particle production via changing gravitational fields and expansion is a real phenomenon, and might be relevant to the origin of matter. In fact, one can invoke this kind of particle creation to (sort of) reheat the universe after inflation. But you still need to start with a gravitational field for this to work...zhermes said:Regardless of the `big-band model' per se, the idea is that the energy density in the early universe was high enough for spontaneous creation of particles. If you're familiar with electron-positron annihilation to produce 2 photons, then you won't be surprised that the opposite can happen---if two photons have enough energy, they will react to form an electron and positron pair. The same type of thing can happen with all particles.
In what way are you saying that the processes of lepto- and baryogenesis are related to vacuum fluctuations? They are the mechanisms by which particles come to dominate over antiparticles, as you say, but this usually done through out-of-equilibrium, beyond-the-standard model particle interactions.This topic is referred to as leptogenesis and baryogenesis (for leptons and baryons respectively), which both focus on how/why 'normal' particles dominate over anti-matter particles---still an unresolved issue.
I agree, this has nothing to do with the origin of energy, in general, I supposed the existence of energy density, and tried to motivate how it can become equipartitioned with matter. As soon as there is energy, it's not just vacuum fluctuations and virtual particles.bapowell said:Right, but this has nothing necessarily to do with the origin of energy in the universe; after all, these are vacuum fluctuations -- virtual particles. How do you suppose they become real?
I'm not. You brought up vacuum fluctuations :)bapowell said:In what way are you saying that the processes of lepto- and baryogenesis are related to vacuum fluctuations?
I see. My confusion then was over your statement regarding the spontaneous creation of particles but I see now that you were referring to real particles. My apologies for misreading your post.zhermes said:I wasn't talking about virtual particle production (i.e. vacuum fluctuations) at all, just boring old particle physics.
John15 said:How does the BB theory allow for the creation of matter. Bt this I mean the sub atomic particles that make up atoms i.e. the quarks and electrons. From what I have read it seems to assume that they already pre-existed and condensed out of the fireball to form atoms.
The general picture goes as follows:John15 said:How does the BB theory allow for the creation of matter.
Exactly. Trying to understand the physics of the singularity invariably leads to nonsense. For this reason singularities are not to be interpreted physically -- they instead signify the breakdown or inapplicability of the physical theory.John15 said:Mark if gravity was involved at the start then at the singularity it would have been infinite re black holes so how could anything escape?.
Why are you associating single matter/antimatter particles with entire universes? There is a single universe, and early on there was a tiny asymmetry between matter and antimatter within that single universe. That's all.Regarding baryogenisis 1 billion antimatter + 1 billion and 1 matter = 2 billion and 1 universes coming out of the BB (2 billion anhilated) that is a lot to come out of a singularity.
These ideas are not addressed under the standard hot big bang model. This model considers instead the evolution of the universe from about the Planck time onwards.The obvious other question is is it reasonable to think that all that temperature and energy spontainiously came into being.
bapowell said:...these are vacuum fluctuations -- virtual particles. How do you suppose they become real? Now, particle production via changing gravitational fields and expansion is a real phenomenon, and might be relevant to the origin of matter. In fact, one can invoke this kind of particle creation to (sort of) reheat the universe after inflation. But you still need to start with a gravitational field for this to work...
...
I would also agree that it is significant, and it is the generally accepted way that primordial perturbations arise (although, history kind of confuses things here...in the early investigations of Parker, Ford, Fulling, Davies, and others, the phenomenon was termed "cosmological particle production", but in recent parlance we talk about the generation of "fluctuations" instead of particles, but the formalism and physical mechanisms at work are identical.) The evolution of quantum fluctuations, from their birth in the inflationary vacuum and their subsequent journey out to superhorizon scales where they become real life perturbations, is perhaps my favorite calculation in physics.marcus said:We're familiar with other cases where geometric circumstances create real (not virtual) particles e.g. Hawking radiation at BH horizon and Unruh radiation caused by acceleration or felt by an accelerated observer. So it seems that expansion of geometry itself, especially inflation, can produce matter. And Leonard Parker seems to consider this significant.
John15 said:A couple of points regarding answers.
Mark if gravity was involved at the start then at the singularity it would have been infinite re black holes so how could anything escape?.
Regarding baryogenisis 1 billion antimatter + 1 billion and 1 matter = 2 billion and 1 universes coming out of the BB (2 billion anhilated) that is a lot to come out of a singularity.
The obvious other question is is it reasonable to think that all that temperature and energy spontainiously came into being.
Has anyone ever tried to create matter out of energy, we create energy from matter in neuclear reactions but is it possible to reverse the process?
His point is that, since that tiny imbalance has resulted in the entire universe we see today, then the original amounts of both matter and antimatter before mutual annihilation must have been staggeringly large.bapowell said:Why are you associating single matter/antimatter particles with entire universes? There is a single universe, and early on there was a tiny asymmetry between matter and antimatter within that single universe. That's all.
If I recall, this can be directly calculated, in a way, through the relationship between matter energy density and radiation energy density (since the energy from all those annihilations would have been dumped into radiation). I believe the true imbalance was of the order of one part in a billion.DaveC426913 said:His point is that, since that tiny imbalance has resulted in the entire universe we see today, then the original amounts of both matter and antimatter before mutual annihilation must have been staggeringly large.
i.e. if the imbalance was on the order of 1/100th of a %, and that left behind a universe of 1060 particles, then the original number of particles must have been 2x1064.
marcus said:...
We're familiar with other cases where geometric circumstances create real (not virtual) particles e.g. Hawking radiation at BH horizon and Unruh radiation caused by acceleration or felt by an accelerated observer. So it seems that expansion of geometry itself, especially inflation, can produce matter. And Leonard Parker seems to consider this significant.
Ivan Agullo is giving an invited talk about this next week at the Atlanta APS meeting. So I'm kind of excited and would be interested if you have a comment.
bapowell said:...
I would also agree that it is significant, and it is the generally accepted way that primordial perturbations arise (although, history kind of confuses things here...in the early investigations of Parker, Ford, Fulling, Davies, and others, the phenomenon was termed "cosmological particle production", but in recent parlance we talk about the generation of "fluctuations" instead of particles, but the formalism and physical mechanisms at work are identical.) The evolution of quantum fluctuations, from their birth in the inflationary vacuum and their subsequent journey out to superhorizon scales where they become real life perturbations, is perhaps my favorite calculation in physics.
How does the BB theory allow for the creation of matter.
...characteristics of the state of the universe at the onset of inflation are not diluted by the inflationary expansion and can be imprinted in the spectrum of primordial inhomogeneities...
The evolution of quantum fluctuations, from their birth in the inflationary vacuum and their subsequent journey out to superhorizon scales where they become real life perturbations, is perhaps my favorite calculation in physics.
...The issue is that whether or not you get Hawking Radiation depends upon whether or not you have a cosmological horizon. And whether or not you have a cosmological horizon depends upon the contents of the universe: it isn't a function of the instantaneous expansion rate at any given time, but on the entire expansion history...
OP:
Provided the Universe always has a non-negative acceleration the radius of this horizon is equal to the Hubble radius at the present cosmological time.
Chalnoth:
No, this isn't true. It reduces to this only in a universe that has nothing but cosmological constant. We also have matter. Since our universe is currently about 70% cosmological constant (assuming it is a cosmological constant...), this isn't too bad of an approximation at the moment. But it would have been a horrible approximation billions of years ago.
...There are ...interaction effects which change the effective masses of both electrons and holes moving in a material because they change the surrounding field which must be carried around with the moving charges relative to what they would be in a vacuum. [any application during the incredible density of a bang?? holes have mass?? How 'dressed were the first electrons to emerge from the bang?? ]
... a propagating fermion [matter] interacts with its surrounding in such a way that the net effect of the interactions is to make the fermion behave as a "dressed" fermion, altering its effective mass and other dynamical properties. These "dressed" fermions are what we think of as "quasiparticles".
...electrons are quasiparticles, the same way the holes are quasiparticles, via Landau's Fermi Liquid theory...[so there are particle [matter] theories in fields, semiconductors, niow liquids, how about the 'plasma' of a bang??]
There are strong arguments that ALL elementary particles are essentially "emergent", meaning that they came out of vacuum many-body interactions.
If there were any particles around during inflation, inflation spread them so far and wide that we'd be lucky to have a single pre-inflation particle in our entire observable universe. The particles that are around today are a result of the end of inflation.Naty1 said:So a natural question might be "Did a particular 'fundamental' particle emerge from the bang first, say a gluon, photon or graviton, or maybe even a 'hole' or a Higgs particle?? When did the necessary conditions for 'particle emergence' begin, before inflation or during inflation or after inflation?
I think the problem here is lazy terminology. There is a "cosmological horizon" which is nonspecific and care should be taken to define fully what is meant. In my calculation, and I think rather commonly also, it defines the boundary of a causal region of the universe; it is equal to the particlel horizon. This distance, \sim H^{-1}, is what is important in my calculation, because when Fourier modes have wavelengths larger than this they cease to evolve because they are stretched across acausal distances. All spacetimes have a particle horizon, on account of the finite speed of light.Naty1 said:My question is how or if Chalnoth's comments apply to your calculation. Does your calculation have a 'valid cosmological horizon'...does it need one?
It's the boundary of the observable universe. There's likely more universe beyond the cosmological horizon.John15 said:By cosmological event horizon can I take it it refers to the edge of our universe? if so then should it not be expanding at the speed of light as light goes outwards from the universe? This of course gives the question what is it expanding into?
bapowell said:It's the boundary of the observable universe. There's likely more universe beyond the cosmological horizon.
We also have the conservation of energy which at some point must not have been valid as all the energy in the universe must have been created at some point unless the universe is not an isolated system.
Right. And just to be clear, if we're talking about particle creation, we're talking about an event horizon specifically.bapowell said:I think the problem here is lazy terminology. There is a "cosmological horizon" which is nonspecific and care should be taken to define fully what is meant. In my calculation, and I think rather commonly also, it defines the boundary of a causal region of the universe; it is equal to the particlel horizon. This distance, \sim H^{-1}, is what is important in my calculation, because when Fourier modes have wavelengths larger than this they cease to evolve because they are stretched across acausal distances. All spacetimes have a particle horizon, on account of the finite speed of light.
Chalnoth is referring to the cosmological event horizon, which only exists in accelerating spacetimes. For de Sitter expansion, the event horizon coincides with the particle horizon; this I believe is what he is referring to.
It's important to point out as well that neither of these horizons is accelerating -- it is the background spacetime that is doing that. In fact, during de Sitter expansion, the event horizon is constant in time!
If there were any particles around during inflation, inflation spread them so far and wide that we'd be lucky to have a single pre-inflation particle in our entire observable universe.
...characteristics of the state of the universe at the onset of inflation are not diluted by the inflationary expansion and can be imprinted in the spectrum of primordial inhomogeneities...
...As inflation ended, the field that drove inflation, the inflaton field, decayed. As it decayed, it produced an obscenely hot thermal bath of particles of all sorts. Only the stable particles survived after that thermal bath cooled.
In my calculation... it is equal to the particlel horizon. ... when Fourier modes have wavelengths larger than this they cease to evolve because they are stretched across acausal distances. All spacetimes have a particle horizon, on account of the finite speed of light.
Chalnoth is referring to the cosmological event horizon, which only exists in accelerating spacetimes. For de Sitter expansion, the event horizon coincides with the particle horizon; this I believe is what he is referring to.
It's important to point out as well that neither of these horizons is accelerating -- it is the background spacetime that is doing that. In fact, during de Sitter expansion, the event horizon is constant in time!
Can you site sources on that?phinds said:It has been concluded that conservation of energy does not apply on cosmological scales.
No idea what you mean by the first question, but the answer to the second is that this fact falls straight out of General Relativity. In General Relativity, there is no absolute way to define global energy. You can define a local energy density, but not a global energy. And you can't conserve what you can't define.John15 said:Any thoughts on my comments about particle stability and decay?
Why has it been concluded that the conservation of energy does not apply on cosmological scales?
..This of course gives the question what is it expanding into? and unless energy/matter is being created then the density of the universe will be going down as the volume increases.
We also have the conservation of energy which at some point must not have been valid as all the energy in the universe must have been created at some point unless the universe is not an isolated system.
Can I take it that creation of matter has either not been tried or that it failed.
John15 said:Any thoughts on my comments about particle stability and decay?
Why has it been concluded that the conservation of energy does not apply on cosmological scales?
..All spacetimes have a particle horizon, on account of the finite speed of light.
And just to be clear, if we're talking about particle creation, we're talking about an event horizon specifically.
and that sounds correct, right?? but I don't know if the current Hubble Sphere meets all your requirements??The particle horizon is the maximum distance from which particles could have traveled to the observer in the age of the universe
Almost any GR textbook should talk about this; it has to do with the lack of a globally defined sense of time in general relativity (since the Hamiltonian generates time translations). See also: http://www.scientificamerican.com/article.cfm?id=is-the-universe-leaking-energyzhermes said:Can you site sources on that?
Yes, this is sort of a complicated issue. It is true that any particles hanging around at the start of inflation were most certainly redshifted away, exponentially diluted by inflation. However, it's not this simple, because if there are particles present at the start of inflation, then the fluctuations are not born in the vacuum as per the standard density perturbation calculation. If the initial state was thermal rather than vacuum (known as the Bunch-Davies vacuum), then the perturbations are affected; in particular, power is suppressed on large scales (see http://arxiv.org/abs/hep-ph/0508070). Non-vacuum initial states can also generate non-Gaussian temperature fluctuations: http://arxiv.org/abs/0710.1302.Naty1 said:I am not so sure: if appropriate conditions [ such as the cosmological energy density during the period of expansion, that roughly 10-35 seconds] remained constant...
and I was also alluding back to Marcus post #12...
The virtual particles are not diluted because they are continuously being created!If the negative gravitational pressure of inflation 'got stuck' briefly on an energy plateau, why not other factors conducive to particle production..like,maybe, virtual particles of the vacuum??...antimatter?? were NOT diluted...
Indeed it's a zoo. One important distinction is that the de Sitter horizon is fundamental to the spacetime, while the Rindler horizon is observer dependent.Glad you mentioned that; I am unsure of the implications and have been rather unsuccessful so far in distinguishing between different 'horizons' and different spacetimes effects on particle production... Unruh, de Sitter, Rindler,etc, have me confused because of apparently different 'accelerations'...
Good catch, and it's an important one. I set up the case where the wavelength of the Fourier mode is larger than the particle horizon, and I chose this horizon because it marks the limit of causal separation. Now, in non-accelerating spacetimes, what happens? The Fourier mode increases in length less quickly than the particle horizon -- if it was once superhorizon, it eventually falls into the horizon: hardly a prescription for particle creation! What we need is to not only push the modes out of the particle horizon, we need to keep them out!. This can only be done if the horizon is shrinking in comoving units, i.e. an accelerating spacetime. In this case, we have an event horizon as well, and this is key to ensuring that the once the fluctuation becomes acausal, it will remain so, becoming a real quantum. So, I admit I didn't give you the full story! All spacetimes have a particle horizon, and this distance is important for determining whether the fluctuation becomes acausal; but we also need an event horizon to ensure that it stays that way! Of course, inflation does eventually end, and so this event horizon does eventually go away. This is key to enabling the real perturbations to eventually re-enter the horizon as I described above. Once inside the horizon, causality is restored to these perturbation and they can begin to evolve into the rich assortment of galaxy clusters, and clusters of clusters, that we observe today.Naty1 said:Based on post #29, you and Chalnoth seem to agree on that, but he says:
which suggests something unique. What does that added 'qualifiation' imply...Does the Hubble sphere meet that criteria??
During inflation, the Hubble sphere effectively satisfies all criteria. During slow roll inflation, in particular, the Hubble sphere and the event horizon are almost coincident, making any distinction between them, especially over the long course of inflation, unimportant.I checked Wikipedia and it says:
and that sounds correct, right?? but I don't know if the current Hubble Sphere meets all your requirements??
Yes, this is correct. So no, the current Hubble Sphere does not work here, because particles beyond the horizon can never arrive, meaning that it depends upon the entire future expansion.Naty1 said:I checked Wikipedia and it says:
and that sounds correct, right?? but I don't know if the current Hubble Sphere meets all your requirements??The particle horizon is the maximum distance from which particles could have traveled to the observer in the age of the universe
Indeed it's a zoo. One important distinction is that the de Sitter horizon is fundamental to the spacetime, while the Rindler horizon is observer dependent
...So no, the current Hubble Sphere does not work here, because particles beyond the horizon can never arrive, meaning that it depends upon the entire future expansion.
...the Hubble sphere effectively satisfies all criteria...
do we know what quarks are made of? do they have mass or are they just energy? From what I understand singly they decay rapidly yet in groups of 3 they basicaly make up the protons and neutrons and protons seem to be virtually eternal, I have found it strange that they should decay rapidly when single yet be stable in 3's. Presumably they were all created in the early stages.
It is strange that certain things like electrons are stable and others not, is there a reason why certain configurations are stable and others not?
Capitalized 'ACCELERATION' is mine:... The process of a Higgs field assuming a non zero value throughout space...is called spontaneous symmetry breaking...it interacts with quarks and electrons...and resists their ACCELERATIONS...[its] what gives an object its inertia...The Higgs field resists only ACCELERATED motion...The Higgs field gives fundamental particles their mass...but when these particles combine into composite particles like protons, neutrons and atoms, other sources of mass come into play...the variety of masses [result because]...different particles interact more or less strongly with the Higgs field...Above 1015 degrees when the Higgs field had yet to condense, not only were all species of fundamental particles massless, but without the resistive drag of the Higgs field, all force particles were massless as well.,...all particles were essentially identical... the electromagnetic force and the weak nuclear force, responsible for radioactive decay, appear so different in the world around us ..because the underlying symmetry..is obscured by the non-zero Higgs field...the vacuum, nothingness, plays a central role in making things appear as they do...
Above 1015 degrees when the Higgs field had yet to condense, not only were all species of fundamental particles massless, but without the resistive drag of the Higgs field, all force particles were massless as well.,...all particles were essentially identical...
If the fundamental particles were massless, doesn't that imply they were moving at c?
Naty1 said:yes, that is what 'radiation' does!
Yeah, I guess that's a fine way to look at it. Observers who are locally accelerating are Rindler observers; these guys measure an Unruh temperature. They are distinct from observers who are locally at rest in an accelerating spacetime; these guys measure a de Sitter temperature.Naty1 said:Brian: in your description above, do you distinguish between different 'types' of acceleration and if so how does that affect results and horizons...for example 'local' acceleration versus cosmologicallly accelerated [Hubble type] expansion...'local' versus 'global'...Do we have to pick particular models to understand different types??
I think we need to be clear on what we mean by "satisfy requirements" -- I have a feeling Chalnoth and I have different things in mind. My statement was that during inflation (especially slow roll inflation), the Hubble radius and the event horizon can be more or less taken to coincide. The actual distinction turns out to be of no practical importance, because the calculation of the primordial power spectrum requires that fluctuations are evaluated in the long wavelength limit: k/aH \rightarrow 0. So the fluctuation is born in the inflationary vacuum and is evolved out to superhorizon scales where it becomes a classical perturbation (this transition is formally identical to the gravitational production of particles, and constitutes the de Sitter temperature). So, the actual calculation is concerned with the perturbation when it is way outside both the event horizon and the Hubble radius, making distinguishing between them unimportant. As a computational approximation that's very good during slow roll, often people simply evaluate the fluctuation at horizon (Hubble radius) crossing (when k=aH) rather than following it all the way out to the long wavelength limit (this is OK because during slow roll the amplitude of the fluctuations really does freeze in). Implicit in this calculation is that an event horizon exists (somewhere between the Hubble radius and the long wavelength limit) which it certainly does during inflation; but exactly where it is is not particularly relevant to the calculation. It only significantly differs from the Hubble radius as inflation is ending; during inflation it probably differs by terms of order the slow roll parameters (\sim \dot{H}/H^2), but I've not worked this out. You can see that during de Sitter expansion, they exactly coincide.These posts, just posted, seem contradictory...are they?
yes, that is what 'radiation' does!
Alpha radiation doesn't. Neither does Beta particles.
