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. . . we cannot measure anything which exists below the Planck Time or if we could it would essentially seem not to change at all. . .
Quote from: Ęthelwulf on 27/04/2012 02:51:46. . . we cannot measure anything which exists below the Planck Time or if we could it would essentially seem not to change at all. . . What's the basis for that statement? I see this get repeated all the time, but no one has ever offered a good reason for it. To the best of my knowledge, the Planck time is where our theories break down, since we know neither quantum mechanics nor general relativity alone will be sufficient there and we don't yet have a testable theory that ties them together. My understanding of anti-singularity arguments is that what GR predicts as a singularity is probably going to be a much richer phenomenon when we figure out a way to describe what actually happens on those scales.
You're assuming the Planck length is some fundamental unit there. Otherwise, I could insert any other unit of distance and make the same argument. I could take a light year and say that it takes 1 year for light to travel the distance of a light year. Therefore I can't measure anything less than a year long. So that returns us to the same question: what makes the Planck scale the length beyond which we can't measure anything?
Quote from: JP on 27/04/2012 17:06:46You're assuming the Planck length is some fundamental unit there. Otherwise, I could insert any other unit of distance and make the same argument. I could take a light year and say that it takes 1 year for light to travel the distance of a light year. Therefore I can't measure anything less than a year long. So that returns us to the same question: what makes the Planck scale the length beyond which we can't measure anything? It's very technical. Even for my poor brain.At planck lengths, geometry as it is understood by General Relativity breaks down. So a photon travelling a light year is absolutely fine but we can't infer it to be fundamental. The planck lengths are however and they are derived using dimensional analysis. Another way to state this, is that the Schwartzchild radius of a black hole is equal to the Compton wavelength at the planck scale thus a photon trying to probe this would gain no information at all. For a quick comparisson, the Classical Electron Radius is in fact times larger than the Compton Wavelength. The Compton Wavelength is (h/Mc) where h is Plancks Constant and it has a value of 6.62606957(29) X 10^(−34) j.s. The Compton Wavelength itself has a value for the electron as 2.4263102175 +(-) 33 X 10^(−12) m value varies with different particles) and is a measure itself of the wavelength of a particle being equal to a photon (a particle of light energy) whose energy is the same as the rest-mass energy of the particle. Basically, all particles have a wavelength. Photon's can never be at rest but the energy of a photon can be low enough to have it's wavelength match any particle who is at rest. It's often seen in the eye's of many scientists as the ''size'' of a particle. Actually, a more accurate representation of the size of an object would be the Reduced Compton Wavelength. This is just when you divide the Compton Wavelength by and it gives a smaller representation for the mass of a system.Furthermore, if a photon could measure a planckian object, it could actually create a new class of particle called a Planck Particle - it would distort that space so badly that the photon would be gobbled up and no measurement could be performed. This is due to the Uncertainty Principle if my memory serves...sorry, you cannot view external links. To see them, please
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Here is a derivation I quickly looked over and which might help....sorry, you cannot view external links. To see them, please
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REGISTER or LOGIN. Experimentally - we are not even close to the Planck Scale - and we don't have any good ideas of how to get there yet; but that is a technical limit not a fundamental one
Well Wulf, Brian has a very fertile mind And.. He.. Will.. speculate..and as he does, sell books..==But yes, he's interesting, and some of his attempts to explain, especially entanglements, was very good. Still I prefer the experiments first. Theory building on that, and I'm not discussing weak measurements when I say experiments.
Oh yes, I agree, physics is the best game there is and you're a gamer Wulf.And I shouldn't be so harsh on Brian, he's a cool guy, although temperamental at times as seen at some blogs He's doing some pretty impressive speculating, as we all want to do at times ==As for above and under Planck, it's like you said, most of the physics we use today draw a line there for what we can explain. Maybe we will get a way to prove scales under it too, Smolin had some ideas there, or rather some of his friends? Using astronomical evidence for drawing conclusions of what might be under Planck scale.
It looks like all the arguments against making sub-Planck measurements use general relativity + quantum mechanics to "prove" that the energies required to probe sub-Planck lengths will create Planck scale black holes. But that assumes GR and quantum mechanics both hold at that scale, which we don't expect to be the case...