Quote (Kamikizzle @ Sun, Jul 12 2009, 04:37am)
now a while back there was a discussion about "virtual particles" which more or less (when observed) break the law of conservation. from my understanding [feel free to correct me along the way] they "exist" in + and - form and dissapate in nearly unfathomably short periods of time. this literally means they are nonexistant, come into existence, and disappear. if they are observed, then they stay in our universe and dont decay at their normal rate (something like 10^-40 seconds). if they are not observed they dissapate
now my basic question of the thread is to ask why they are allowed to exist in the first place. it is said they "come into existence" due to the uncertainty principle. now i have a very basic understanding of this principle, so i have two main questions
what does unkown momentum and position have to do with virtual particles and why they exist
and why is it this this principle "trumps" laws like conservation of energy and momentum
warning this is tl;dr lol.
Lets start with the bolded, in particular there is no "trumping" here -- you have to remember our most fundamental and oldest laws of physics only apply to our observable world; on the macroscopic scale.
Let me give you an example, you measure the time it takes for a car to move from point A to point B down to the nano second -- you do it again, however this time, an extremely minuscule particle appears out of thin air and hits the car, but its so small that you measure the same exact time. So, does that mean the car was hit? In theory the car should have slowed down, but experimentally we saw no change...so which supposition is the right one?
So obviously the correct answer to that would be, well the car did slow down, but we just couldn't prove it -- well then, how do we prove virtual particles? There are several reasons why virtual particles are necessary -- in a most basic explanation, they mathematically uphold a few laws that would be broken otherwise.
There are many many reasons that they exist, but I'll give you one example -- stephen hawking questioned that if objects went into a black hole, and then were condensed to a single point, then entropy inside would decrease -- therefore we should see an increase in entropy OUTSIDE the black hole (e.g. radiation is an example of an entropic process). But how could a black hole have radiation, if not even light could escape it? This is where VP (virtual particles) come in. Apparently, the virtual particles that appeared JUST outside the black hole's event horizon would actually be affected in the short amount of time that they existed due to the black holes immense gravitational pull. Either the plus or the minus particle would get pulled into the black hole (i forget which, and there was a reason that specifically only one of them go in too) and its partner would escape (again, theres a reason this would happen, but I've forgotten the details). Since the VP pairs didn't collide and annihilate with each other, they are now a part of the collective matter in our universe. This phenomena is now called hawking radiation, and it makes it seem as if black holes radiate even though it isn't actually emitting the radiation from inside the black hole.
EDIT: How VPs correlate with the uncertainty principle is actually a tough thing to explain (and i don't feel like typing any more T_T, maybe i'll post again) but in a nut shell, we know Heisenberg's principle says the more precisely you measure velocity the less precisely you measure position and vice versa -- well another scientist found that energy and time are related in the same way (i guess its obvious once you think about it) and are actually analogs of Heisenberg's rules. So here we have particles that appear and disappear in A REALLY REALLY short amount of time, (this gets a little trippy, read carefully) so now as a scientist, i take a random point in space, and measure energy fluctuations in a certain time period -- as I decrease the period of time i want to measure, my readings of energy fluctuations become less and less accurate. So when you get down to the amount of time that VP's exist for, you basically get to the point where you can't even say that there were no energy fluctuations even if it is a perfect vacuum.
So basically VP's are a purely mathematical observation that are necessary to uphold already existing laws. Hope this explanation helped some what, I can't really say I know anything but the surface knowledge of how this works (the mathematics is way beyond me lol...wayy wayy beyond me haha)
This post was edited by BovineDesi on Jul 16 2009 07:43am