- #106
nismaratwork
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- 0
What is spacetime made of? Math, because it's a model. If the real question here is "what is reality anyway" then the only real answer is, "who the @!&* knows?!".
petm1 said:How about change.
tauon said:if as you say, the supposed "fabric" of spacetime is experimentally unobservable ...
it is [mathematical] relations between objects and events.
Change of what and to what? Change of 'observations'?
brainstorm said:More specifically, if materialization is one expression of energy, and gravitation is a function of materialization insofar is mass is imparted; then kinetic energy of motion is what counteracts the gravitational attraction that tends toward reducing spacetime to non-existence.
GeorgCantor said:but this will hardly be accepted as a rigorous statement as perpetual motion machines are tossed out without an examination.
imiyakawa said:Virtual particles do not violate conservation, whilst perpetual motion machines do.
GeorgCantor said:Kinetic energy of motion cannot exlain the ever increasing rate of expansion of the universe and Dark Energy is pretty much the new "Standard Model" these days(a sort of ultimate free lunch). It's a baffling example of nothing becoming a something. It's theorized that vacuum fluctuations should account for this force, but this will hardly be accepted as a rigorous statement as perpetual motion machines are tossed out without an examination.
GeorgCantor said:I was speaking of virtual particles causing the acceleration of the expansion of the universe, not merely going in and out of existence with observationally negligible effects.
nismaratwork said:The universe as a whole does not necessarily have to conserve energy; consider Dark Energy, and the redshifting of photons with spatial expansion. Interestingly, those "virtual particles" don't account for enough energy to balance the possible loss due to expansion. We're talking about a scale that is not open to this kind of analysis.
brainstorm said:You can analyze a model on whatever scale based on the assumption that all relevant parameters are known. If that assumption proves false, and it turns out that there are other influential parameters that you didn't take into account in your model, the model becomes that much less useful, but you can still attempt modeling and extrapolation from the model - it's not impossible.
What I would like to know is do you recognize space as being limited to gravitational topography, in the sense of Einsteinian curved spacetime, or do you presume space to exist independently of matter and its gravity? My assumption is that mass/gravity determines the curvature of space, and therefore it is never possible for EM radiation to escape matter indefinitely. Do you agree or do you think light can proceed infinitely away from any and all matter?
If matter is being converted into energy by stars everywhere, then presumably the mass of the universe is decreasing, unless there is some other process by which energy is getting converted into matter. I have personal hunches about how this could be happening, which involves black holes, but I won't go into those now. The point is that various scenarios for the distant future of the universe can be projected from assumptions in the model of how energy and matter behave relative to each other.
If, for example, all matter got transformed into EM radiation, would the radiation continue infinitely in divergent directions, or would it attract itself into convergent patterns? I think it would do the latter if space itself can indeed only exist as a function of gravitation, for in that case radiation itself would probably exert sufficient attractive force to generate curvature in its trajectory, which would probably eventually culminate in contraction to the point of forming new matter.
When you give the example of red-shift, are you implying that light loses energy by red-shifting? Why wouldn't you think that the waves are growing in amplitude in proportion to their frequency decrease? Couldn't a photon lose frequency simply be expanding, and therefore retain the same energy?
nismaratwork said:Here's a question for an answer: which is more energetic? A photon of the UV wavelength, or that of the Radio wavelength?
brainstorm said:Wiki says radio waves are the least energetic and the lowest frequency. I do not understand what "photon" refers to exactly, i.e. whether it is a single EM wave or something else. The reason I thought it was decided that radiation behaved as particles is because energy is always delivered in fixed increments by radiation, which appear as packets. I think Planck discovered this, but I'm not 100%.
nismaratwork said:My point is that light (in whatever form you choose to envision it) redshifts with universal expansion, which is true for all EM radiation, and in a sense, matter.
brainstorm said:How so with matter? And what does this suggest about the conservation of energy and matter?
nismaratwork said:Here is an explanation, and in my view and a decent refutation of what I'm talking about: http://www.astro.ucla.edu/~wright/tiredlit.htm
Of course, the balloon analogy has its limitations, and there is no explanation as to how or why this effect does not take place. This is why I said "We're talking about a scale that is not open to this kind of analysis."
brainstorm said:Nice link. Thanks. But you completely ignored the questions in my post: 1) What did you mean when you said that matter, in a sense, redshifts with universal expansion; and
2) What is implied about the disappearance or appearance of matter/energy at any scale?
nismaratwork said:Ok, you just mean that matter can undergo redshift once it is converted into radiation.
In the link you posted, it said that redshift doesn't reduce the energy of radiation, it just dilates the waves such that it takes more time for the same amount of energy to reach a destination point. So, unless I am understanding something wrong, no energy is lost - it's just delivered at a slower rate over a longer period of time.I'm not arguing that this is correct, but it is puzzling. On one had the universe seems to be expanding, radiation redshifts, but the effects of this loss are not observed.
How exactly is the loss apparent?Dark Energy or vacuum expectation energy doesn't match or make up for the apparent loss. although neutrino pair creation has been put forth.
Regardless of what "many" or few take as a view, it's ultimately the reasons behind what they think that matters, not their conclusive opinions. Everything theoretical ultimately remains a mystery. The issue is what can be reasoned despite fundamental unanswerability, and how.Many take the view that conservation of energy doesn't apply to the universe as a whole, and until there is a way to confirm its symmetries (or not) it will probably remain a mystery.
One thing I don't understand is whether you agree that any matter/energy lost or gained at the level of "the universe" has to be lost or gained in some sub-set of it. So unless there is a specific mechanism for matter/energy to be lost or gained, conservation law is logical. The question I would be asking is what happens to radio-waves when they red-shift? Is their a lower limit to radiation frequency or does everything exist amid photons so old that their frequency has long since surpassed measurability?
This raises another question, which is why gamma rays are the upper-limit of EM frequency? I wonder if it is possible that yet higher frequencies begin behaving as material particles with the ability to slow down, for some reason. I only wonder this because gamma rays are supposedly the size of an atomic nucleus and the amount of energy expressed in them is growing exponentially; and because I wonder where the bridge between energy and matter (in that direction) takes place.
brainstorm said:So unless there is a specific mechanism for matter/energy to be lost or gained, conservation law is logical.
Dmitry67 said:No
I can give an example: you stand in front of the building (1000'000kg). It has 0 kinetic energy. Now you run towards it at 10m/sec. In your frame of reference (where you are at rest), kinetic energy of the building is now huge. Where did this energy come from? :)
Of course, you would say: this is not fair! When you started to run, you changed your frame, so you just can't compare energy of the building in 2 different frames!
Now the Universe. There is no frame which can cover the whole Universe. In Cosmology there is a pseudo-frame ('all universe at time t') but it is not a valid physical frame because if you draw this frame, you would see that it is not a flat surface in spacetime but it is curved!
Dmitry67 said:No
I can give an example: you stand in front of the building (1000'000kg). It has 0 kinetic energy. Now you run towards it at 10m/sec. In your frame of reference (where you are at rest), kinetic energy of the building is now huge. Where did this energy come from? :)
Of course, you would say: this is not fair! When you started to run, you changed your frame, so you just can't compare energy of the building in 2 different frames!
Now the Universe. There is no frame which can cover the whole Universe. In Cosmology there is a pseudo-frame ('all universe at time t') but it is not a valid physical frame because if you draw this frame, you would see that it is not a flat surface in spacetime but it is curved!
brainstorm said:Framing is an epistemological issue. In your process of running toward the building, you convert a certain amount of energy into momentum, which is conserved during your collision with the building. No energy is lost or gained during that process. The only reason you are able to suggest it is possible is by confounding your analysis by using framing to change the descriptions of what is going on. Running toward the building doesn't increase the KE of the building the same as would pushing the building over. And besides, the KE only matters once it gets expressed through transference to something else. Prior to collision, the KE expressed is just a build up of dynamic potential to transfer energy to another carrier, isn't it?
If no energy is created or destroyed at the micro-level of empirically observable matter-energy, how could it occur at a more complex level or larger scale?
nismaratwork said:It's a principle that just doesn't apply; energy cannot be created, yet here we are. At the scale of the universe as a whole, it's not that the notion is invalid, it just does not apply to it.
brainstorm said:Implicit deus ex machina is not an interesting scientific proposition. I am interested in what process(es) could convert energy into matter and how/when this may occur naturally. I suspect either something to do with black hole gravity, ultra high energy radiation, or both. I would also like to establish whether radiation can ever permanently escape gravitational fields. If it can't, then it would seem that energy inevitably gets converted into matter, which inevitably gets coagulated into a body with sufficient gravitation to result in nuclear fusion, converting the matter back into energy. This would, I think, establish the universe as a perpetual system of matter-energy conversions, which could also mean that it has no beginning or end. The big bang is suggested to be an absolute beginning, but technically I don't think BBT addresses what happened prior to the amalgamation of the energy/matter that began expanding in the first place. It may have been due to the convergence of a prior universe of dynamic matter-energy into a singularity with the propensity to expand. I think the key to theorizing this would involve finding some mechanism whereby black holes can destabilize or otherwise generate radiation. The only theory of this I know is that of Hawking radiation, but could that process be significant enough to result in big-bang levels of energy-expansion?
nismaratwork said:You are, in a different area, making my point: there is no theory to cover the period "before" there was a "before (before BB), and conservation of energy doesn't apply to the universe as a whole, only its subsystems. You can show how energy is conserved in a given system, but not for the entire universe, which logically should be losing energy, but empirically seems not to be. How matter is created from energy is spelled out in E=Mc2, but the conditions for that are no longer present (in any part of the universe that I know of).
nismaratwork said:You can show how energy is conserved in a given system, but not for the entire universe, which logically should be losing energy, but empirically seems not to be.
I don't think you can call the universe an empirically observable entity. The universe is a theoretical superset of everything that exists. As such it is an extrapolation of what is imagined to exist in the same way as the set of all observable matter-energy phenomena, which is theoretically a subset of the universe in its imagined entirety. In short, empirically observable occurrences can only be a subset of the total set of everything theorized to exist as part of "the universe," so the universe can't be empirically circumscribable.apeiron said:Perhaps it is indeed better to start with the empirlcal here? We observe the universe to be largely flat, homogenous, isotropic, and so can impute a conservation principle at work.
So you think energy is dissipating into nothingness? What makes you think it is not simply transferring or transforming into new expressions? This is why I asked you if you think radiation can proceed indefinitely away from all gravity fields? I don't think it can/does.Then what seems to be in exact balance is cooling and expansion. So there is a fundamental equilibrium between energy and spacetime. The universe is a dissipative structure which is its own heat sink. Radiation spreads and cool. An initial thick hot point runs down a gradient of dissipation to become a thin cold void.
apeiron said:Perhaps it is indeed better to start with the empirlcal here? We observe the universe to be largely flat, homogenous, isotropic, and so can impute a conservation principle at work.
Then what seems to be in exact balance is cooling and expansion. So there is a fundamental equilibrium between energy and spacetime. The universe is a dissipative structure which is its own heat sink. Radiation spreads and cool. An initial thick hot point runs down a gradient of dissipation to become a thin cold void.
Of course, dark energy is the new complication - both necessary because there was not enough energy/matter/gravity to balance the observed expansion rate, and a complication as it seems to throw in an extra little persistent acceleration, implying an open thermodynamic story.
So on the whole, the universe looks like a closed story - a gradient simply being run down from a hot point to a cold void, a phase transition we are seeing from the inside. But there is still a small nagging openness. I think this will be due in the end to a marginal QM uncertainty as various people have speculated.
You can just postulate that the unobservable parts of the universe behave similarly to the observable parts and tentatively assume that if matter-energy is being conserved in all observable/fathomable mechanisms present that it would be conserved in the unobservable parts too. You just have to acknowledge that your assumption is tentative and state your assumptions so that they can be subject to critique.nismaratwork said:I disagree, first, because I can't imagine a way of defining the symmetries needed to invoke Noether's Theorem for the universe as an entity, and because Brainstorm is right; how is it empirically observable as a whole? We see only a small slice of it, and we know that; for the rest... ? How do you formulate a conservation law for something that is ill defined in the sense needed for such a thing?
brainstorm said:This is poorly written so here's an example: Presumably there are stars/galaxies in existence beyond the Hubble horizon where stars have red-shifted beyond visibility. Still, they are presumed to exist as part of the universe despite having become empirically unobservable. Therefore, only the subset of empirically observable phenomena are empirically observable, not the the universe as a whole, which includes the unobservable stars/galaxies too.
brainstorm said:So you think energy is dissipating into nothingness? What makes you think it is not simply transferring or transforming into new expressions? This is why I asked you if you think radiation can proceed indefinitely away from all gravity fields? I don't think it can/does.
nismaratwork said:I disagree, first, because I can't imagine a way of defining the symmetries needed to invoke Noether's Theorem for the universe as an entity, and because Brainstorm is right; how is it empirically observable as a whole? We see only a small slice of it, and we know that; for the rest... ? How do you formulate a conservation law for something that is ill defined in the sense needed for such a thing?
This is what I was saying. It IS possible to THEORIZE the behavior of the universe as a whole through tentative extrapolations from observables. However, the other poster was suggesting that empirical observation of the universe as a whole could serve as a starting point for theorizing. I don't see how this is possible if the universe only exists at the theoretical level of extrapolation and is not empirically circumscribable.apeiron said:I don't see the problem here. We start with what we observe (an equilbrium as far as we can see) and then extrapolate over the event horizon. We can't know for sure what lies over the horizon. but our extrapolations can still be logical.
So yes, there would be a supraluminal expanse of universe beyond our current event horizon - based on logical extrapolation. And we can also make guesses about what came before the big bang on the same basis.
I don't understand what is meant by "observed flat balance." Do you know of a link that explains the logic of what is observed and what is extrapolated from that and how? The only thing I've read has to do with galaxies rotating at an apparent speed faster than C, but I forget how this is logically brought to bear on estimations of their mass/gravitation.Well we know that if the universe contained just radiation, then there would not be sufficient gravity to create the flat balance we observe. Even throwing in dark matter, only got things up to around 30%. So dark energy, or something like, was needed to balance the books, providing the missing 70%. So I think that is a basic misconception you have here.
I looked at the picture. I did not see how it related to the minimum possible wavelength of photons. Maybe my brain hit its minimum wavelength:)A good introduction to this in general is...
http://www.mso.anu.edu.au/~charley/papers/LineweaverChap_6.pdf
See especially the diagram on p71 to answer your query about the minimum possible wavelength of photons.
The general view I am expressing is that energy is being turned into spacetime in essence. That is the phase transition taking place. This is hard to see if you are imagining energy as stuff (substance) and space as a stage or framework (form), but if you frame both as geometry (positive or open vs negative or closed curvature), then it becomes easier to appreciate how the two might be related.