In the inimitable and infamous tradition of slashfic, there is probably a reprehensible story/video somewhere in that. 
We used to joke when I was in college that particle physics was the act of kicking a dog and using the bark emitted to determine everything about the dog, more or less the hammer/nail analogy. But Hawking radiation wouldn't function that way, the more massive a black hole the more gravity it has, more gravitons, HR works the opposite way, very large black holes emit almost none, very small ones emit huge amounts and it goes with a bit over the cube of mass inverted. Double an objects mass and you'd expect double the gravitons, but 1/8th the Hawking Radiation if it had an event horizon. In any event this gets into 'virtual gravitons' that in theory could ignore the event horizon but the whole Quantum Gravity much like Grand Unified stuff is hazy, troublesome, etc.
"Cosmology takes GUTs," and explorers are, by definition, the people who traverse regions marked "here there be dragons." I think it was Planck whose college advisors told him to go into something other than physics because all the big questions had been answered and nothing remained but fleshing out the details, but God and the devil both dwell in those details. "Hazy, troublesome, etc." strikes me as another way of saying, "presents fundamental paradoxes that are either currently insoluble, admit no currently verifiable solutions, or both." Again, wave/particle duality was once considered an all but trivial artifact; a century and several new disciplines later we STILL lack a completely satisfactory reconciliation, but have tremendously advanced our understanding of matter, energy and space looking.
Commentary aside, a follow up question to the follow up question: WHY is Hawking Radiation inversely proportional to mass? Understand, I do not dispute that it is, I am just curious whether the mechanism necessarily requires that if gravitons were produced by a similar mechanism they must be similarly inversely proportional. It often seems to me gravity is at odds with the other fundamental forces, tending to contract what they expand, acting to bring to rest what they set in motion; I strongly suspect it is not so much that there is no such thing as "anti-gravity" so much as that the unification of the other fundamental forces is it. If (and I realize it is a big "if" ) that supposition is valid it seems conceivable that a process minimizing kinetic energy might maximize gravity (in a sense, black holes do just that.)
I do not propose black holes could emit gravitons IDENTICALLY to the way they emit Hawking Radiation (which, as I understand it, is an oversimplification anyway; consuming one product of virtual particle decay before it can recombine with the more distant product is not "emission," per se.) I have in mind tidal forces shredding objects, down to the subatomic, subnuclear, level, until destroying the very particles with which gravitons interact, leaving gravitons nowhere to go except into the black hole or out to space seeking some other purchase. Since their interaction is unlimited and always attractive, it would effectively draw objects toward the black hole, and the larger the black hole the greater the number of objects tidal forces would destroy, expelling more gravitons (again, from the objects, not the black hole itself.)
The whole concept of gravitons perplexes me, since I always took it for granted all matter exerts gravity: Does that include gravitons themselves? If so, what is the medium? Obviously not a graviton, unless it is self propagating like I have suggested photons may be. Not to mention the fact gravitons are every bit as necessary and hypothetical as the Higgs boson is (or was,) but practically impossible to detect with the LHC or anything else. They seem far more deserving of the "God particle" title, especially since the Higgs was only the Standard Models last unverified particle because the Standard Model deliberately excludes gravity from consideration. It is a bit like a cartographer declaring, "I have mapped the entire universe," on the grounds of defining everything outside the Solar system as "not part of the universe."
1) I thought we had established matter is NOT uniformly distributed throughout the universe, that the universe is "clumpy." Basically, BGs question. The mere existence of things like planets, stars and clusters (the last of which all but implicitly concedes nonuniformity) amid vast vacuums tends to suggest that anyway. "Homogeneous" and "uniform" are not interchangeable, after all; homogeneousness permits, but uniformity precludes, clumping. The mediocrity principle only carries us so far, and is a tendency, not an absolute; the Sol is a mediocre star, as observation of countless others like it confirms, but life is uncommon (to say the least,) as the absence of any extraterrestrial examples also confirms.
Uniformly distributed at a certain scale, once randomness and local effects cancel out. Spill a trillion peas into the Sahara and some will clump together, some areas will be empty, some will form smiley faces, zoom out enough and the effect is even distribution. Somethings do this nicely, gases at room temperature and pressure in a spherical shell without gravity or any external radiation source will be pretty smooth but if you zoom in enough you'll see clumping and patterns. Put it back into gravity and you'll find more particles near the bottom and near the top fewer faster moving ones. Examine a smooth table with a microscopes and it resembles mountain ranges and valleys and they unique, not patterned.
Uniformity is neither relative nor quantitative though; again, that is the difference between homogeneous and uniform. If only scaled uniformity (i.e. homogeneity) is required we could just happen to inhabit a relatively rarefied region (even though it appears just the opposite from our perspective,) and a heavily irradiated blindingly bright universe could well be the rule to which we are the exception. The law of averages dictates at least one such regions existence in a homogeneous universe of sufficient size, however clumpy it may be at local scales.
If we have a cubic meter of space consisting of a half cubic meter of solid matter and a half cubic meter of utter vacuum we might say "matter is uniformly distributed at a scale of a cubic meter," but the truth would be its distribution was perfectly EQUAL (since neither it nor vacuum predominates) yet perfectly UNEVEN (since both are wholly concentrated.) The paradox implicitly assumes uniformity at ALL scales, or at least most, else local rarification would be the obvious and simple solution.
Fair as far as it goes, but when such contradictory evidence arises (such as Olbers Paradox, at least till its resolution) either it or the principle must be invalidated.
It can radiate away all of it, it is true that if a speck of space dirt absorbs a photon it will pick up momentum equal to the photons, but if another strikes it from the opposite direction it will come back to a relative stop and need to spit out all that energy. It will do it based on its temperature, if its absorbing more than it's emitting its temperature will rise, and it will emit more radiation as a result. Goes with the 4th power of absolute temperature. Which is to say an object sitting a 3 Kelvin, insterstellar void, is 100 times cooler than Earth, 300 K, and thus the Earth emits 100^4 or 100,000,000x as much background radiation as it would if you shut the sun off and let the Earth cool to Universe standard. A red Dwarf, warmed by its internal fusion to 3000K, would give up 10 Billion times as much as if it simply were shut off. Everything in the Universe is being constantly pounded by photons, outside of proximity to a star, maybe 100 AU or so, this evens out so they tend to come about evenly from all directions, though there'd always be some gradient of course, but the random dust mote is being smacked around constantly by photons in good old fashioned Brownian motion. And a lot of them too, space is not very dark at all, some orb with a square meter of surface area sitting the void at 2.7 K will emit σT^4, σ ≈ 5.67 × 10−8 W
m2K4), or 3 microwatts, and because a microwave has only about 10^-23 joules of energy per photon, that means every second it is emitting about 3x10^17 photons, or about 300 million billion of them a second. It's also being hit by the same number a second from basically every single direction so all that momentum it is absorbing neutralizing out and the energy has nowhere else to go but out via photons.
If I shine a light on it, say a 40 watt flashlight, it will begin to warm up (and move away) until it begins radiating 40 watts minus whatever small amount is going into momentum, if I stick to flashlights on it, either side to hold it stable, it will warm up until it gets to 80 watts of radiaiton. In this case 80 = σT^4 --> 10/σ = T^4 = 1.4x10^9 --> T = 193k, or -80 celsius, if I stuck 6 flashlights around it, top/bottom, left/right, front/back it would rise to 254k, or Montana in the Winter. It would take some time to get there, it's true, based on its mass and such, a hollow beachball doing so much faster then a lead ball, but it would reach equilibrium and pretty quickly in most cases. Minutes, days, when talking about objects that aren't big like dust or rocks. A one ton object with a specific heat of 1 (water) stores 4 million joules per degree and most objects are within an order of magnitude of that, so our orb here absorbing a 40 watt flashlight gets there in around 100,000 seconds, just over a day, call it two since its radiating significantly as it warms too, just not as much. Most stuff in the Universe absorbing light is smaller in mass compared to absorption, a big space rock doesn't absorb as much light as an equal mass of gas, so this effect takes a lot less then a day.
Back to our closed solar system though, with an equal amount of sun and gas. Now it depends on the star, but our own emits 4x10^26 watts and has a mass of 2x10^31 kg, and again it takes about 4000 joules per kg to raise things a degree. It's going to take about 200,000,000 seconds for the sun to heat that other gas up a single degree, to get it to its own 5000k it's going to need a trillion seconds. That's only about 300,000 years though. Of course the calculations of how much dust were based on how much was needed to block that much light at a certain radius and its far lower, enough for the heating to occur in mere days. The infinitely reflective surface is imaginary but analogous to Olber's Paradox conditions, there's light coming from everywhere replacing what leaves/
If reduced to Brownian motion though that would also tend to resolve the paradox: Intervening matter struck by incoming photons is also struck by OUTGOING photons so the latter effectively reflect the former (even if it is technically a case of intervening matter absorbing both and emitting new photons with velocities opposite that of the first two.) Of course, for that to work energy emission from and toward the center must be equal, which it obviously would not be in our uniformly distributed onion, but otherwise the far greater incoming energy would not be offset by outgoing energy and the intervening matter would have a net momentum preventing some incoming energys transmission to the core: No core radiation bombardment.
It was my understanding that is essentially the Second Law of Thermodynamics' consequence: Gradual but inevitable conversion of kinetic energy to potential energy until universal heat death. There the graviton again rears its ugly hypothetical head, forcing us to consider whether that produces a truly static universe or the graviton somehow transcends the Second Law in a Big Crunch. Accelerated expansions Dark Energy only complicates rather than resolves that question.
I usually consider science's greatest accomplishments to be penicillin, man on the moon, pacemakers, plentiful free online porn and such but yes a case can be made that uncovering various paradoxes as of yet unresolved is quite an accomplishment. Keep in mind that many of these paradoxes, like Olber's have been solved and aren't paradoxes at all, this may or may not be true of the rest of them and any others we uncover but I don't subscribe to the notion that there's always some new mystery to be solved, just ones we can't solve or haven't solved yet
The thing is, science, especially prior to the modern era, rarely addresses truly novel questions, or those for which no potential answer has been proposed: It usually addresses long standing questions by exposing the deficiencies of accepted answers and proposing new ones that remove those deficiencies.
Granted that is less so in the century or so since science found so many rigorous, verified and widely accepted answers to so many old questions; today it is increasingly tasked with resolving the conflicts and failings of its own improved answers rather than previous ones of older disciplines. Yet the process remains unchanged; we can explore no region before aware of its existence. Science has simply progressed from correcting/clarifying errors of other disciplines to correcting/clarifying its own. It is more often refinement and verification than true discovery; Plancks advisors had that part right, but vastly underestimated its import.
Last First in wotmania Chat
Slightly better than chocolate.
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LoL. Be well, RAFOlk.
- 28/07/2013 04:17:47 AM
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*NM*
- 28/07/2013 10:29:48 PM
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