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.
Because a proton, electron, and neutrino/anti-neutrino pair is a lower-energy state than a neutron.John15 said:Have looked at particle decay on wiki. No mention of quarks.
Why does a neutron decay when on its own and not when part of an atomic neucleus?
John15 said:Lots of interesting disscussion but it still leaves me no further forward.
Mass and energy are equivalent. Energy as I understand it is massless ripples through spacetime. How do you get from massless ripples to say an electron. If the BB theory is correct then all that could be there to start is massless energy.