26 Jul 13
Originally posted by DeepThoughtThis is something else new to me. I didn't know something like a photon could have mass. I assumed mass comes with energy becoming locked into a relatively stable form, such as the parts making up an atom. But if the Higgs field gives matter its mass, can it also give something not strictly defined as matter mass as well?
If the photon has a mass it has a half-life if there is something lighter for it to decay into. If it does not have a mass then it does not have a half-life, as there is nothing lighter for it to decay into. Electrons and protons are stable because they have quantum numbers which prevent decay - there's nothing for them to decay into. Neutrons are mor ...[text shortened]... ability supernova on Wikipedia) and has been observed in cloud chamber pictures.
26 Jul 13
Originally posted by lemon limeThe W and Z bosons which carry the weak force are massive as a result of interacting with the Higgs.
This is something else new to me. I didn't know something like a photon could have mass. I assumed mass comes with energy becoming locked into a relatively stable form, such as the parts making up an atom. But if the Higgs field gives matter its mass, can it also give something not strictly defined as matter mass as well?
26 Jul 13
Originally posted by lemon limeI think the reasons why don't call photons 'matter' are:
But if the Higgs field gives matter its mass, can it also give something not strictly defined as matter mass as well?
1. The historical belief that light was a wave.
2. The fact that photons are always moving really fast so we never really see them as stationary objects. (I am not sure if experiments which slow down light ever actually slow down photons, I suspect not).
3. 1 and 2 and quantum mechanics means that the particle like behaviour of light is rarely observed and it usually behaves more like a wave in the macroscopic world.
4. The fact that they are the smallest part of any interaction so we see the larger item as being more 'solid'.
5. They are essentially annihilated in any interaction, whereas other larger particles interact without annihilation.
I see Wikipedia has interesting comments on what 'matter' is:
http://en.wikipedia.org/wiki/Matter
26 Jul 13
Originally posted by twhiteheadI could be wrong, but I don't think light can slow down. I believe the speed limit isn't just a limit as to how fast light can go, I think photons are literally locked into going at that one particular speed... sort of the ultimate cruise control, it can't go one iota faster or slower.
I think the reasons why don't call photons 'matter' are:
1. The historical belief that light was a wave.
2. The fact that photons are always moving really fast so we never really see them as stationary objects. (I am not sure if experiments which slow down light ever actually slow down photons, I suspect not).
3. 1 and 2 and quantum mechanics means tha ...[text shortened]... ipedia has interesting comments on what 'matter' is:
http://en.wikipedia.org/wiki/Matter
Someone told me about an experiment that proved light traveling through a super cooled gas could travel much slower than c. He used this example to illustrate how light only travels at c through a vaccum, because I had told him light always travels at c. He said it only goes at that speed through a vaccum but through other mediums it will slow down.
However, the appearance of moving slowly through a super cooled gas is deceptive. The photons run into and are absorbed by electrons, causing them to jump into a higher energy state. Those electrons then pop back into their natural orbits and release the same amount of energy in the form of another photon. So it was the delay factor that made it appear as though light was moving very slowly. The light actually was traveling at c through a vaccum before running into each next electron blocking its path. And bringing the temperature down to something close to absolute zero served to increase the amount of time light was delayed, in fact so much so it appeared as though the light beam was practically crawling through that super cooled tube of gas.
26 Jul 13
Originally posted by lemon limeThis came up on a previous thread in this forum and it was totally new to me. Since then I did some learning of quantum mechanics to find out how it works.
However, the appearance of moving slowly through a super cooled gas is deceptive. The photons run into and are absorbed by electrons, causing them to jump into a higher energy state. Those electrons then pop back into their natural orbits and release the same amount of energy in the form of another photon. So it was the delay factor that made it appear as ...[text shortened]... ppeared as though the light beam was practically crawling through that super cooled tube of gas.
It turns out it is not quite as simple as you portray, there is quantum mechanics involved.
When a photon passes through glass, it may be absorbed and re-emitted as you say, but because the emitted photon is indistinguishable from the original, they interfere. So it turns out that when a photon is going through glass it takes all possible routes, is absorbed and re-emitted by all possible electrons, then emerges the other side as if it has simply been slowed down! There is also a possibility of it being reflected at one of the two surfaces. The reflection is also an entirely quantum effect ie the emitted photons interfere with the photon that was coming into the glass and the end result is a reflection as if it was a wave.
The interesting thing here is that although there is a delay between absorption and reemission the emitted photon is still interfering with the absorbed one - even though in classical mechanics they never exist at the same time!
Quantum mechanics is cool!
26 Jul 13
Originally posted by twhiteheadYeah, there are aspects of QM I'm not able to grasp, or maybe visualize is a better word. I suspect light traveling through gas works a bit differently than traveling through glass, one obvious difference being gas is missing the letter l and an s.
This came up on a previous thread in this forum and it was totally new to me. Since then I did some learning of quantum mechanics to find out how it works.
It turns out it is not quite as simple as you portray, there is quantum mechanics involved.
When a photon passes through glass, it may be absorbed and re-emitted as you say, but because the emitted p ...[text shortened]... ven though in classical mechanics they never exist at the same time!
Quantum mechanics is cool!
J/K
That part about interference is weird. I don't know how the first photon could interfere with the second one (or maybe the 2nd one is interfering with the 1st?) expecially if they are always separated by even so much as a very tiny amount of time. I believe it's impossible for any cause and effect to overlap on the macro scale, but the on micro scale common sense predictions often don't apply. I've often wondered about quantum entanglement, and how it seems to operate as thought space doesn't even exist. But then it occured to me that perhaps for things as small as quanta maybe space literally doesn't exist. Maybe what normally defines space at the macro level isn't an absolute, and at the quantum level the existence of space itself could be entirely dependant on what may or may not be happening there.
27 Jul 13
Originally posted by lemon limeI believe photons can interact with the chemical bonds in a solid like glass as well as with the photons. So yes, it is different from a gas in some ways.
Yeah, there are aspects of QM I'm not able to grasp, or maybe visualize is a better word. I suspect light traveling through gas works a bit differently than traveling through glass, one obvious difference being gas is missing the letter l and an s.
J/K
But generally a photon gets from point A to point B by every possible way. As long as you cannot know which route it took, or how many times it was absorbed/reemitted etc, then it will take every route available. Where it finally shows up is random, but with a probability based on the number of possible routes that lead to that outcome, combined with the wave function of the photon along each route.
27 Jul 13
Originally posted by twhiteheadThis is where I always run into trouble, because I'm never sure what is meant by every possible route. Does a photon really take every possible route, or must we assume every possible route is taken because we don't know (or can't know) which route is taken by the photon? It's like schrodinger's cat... if I must assume both states exist at the same time does that mean both states actually do exist at the same time, or must I assume they do because I won't know until I look? I'm actually assuming only one of those states exist, but I have to assume both until I look.
I believe photons can interact with the chemical bonds in a solid like glass as well as with the photons. So yes, it is different from a gas in some ways.
But generally a photon gets from point A to point B by every possible way. As long as you cannot know which route it took, or how many times it was absorbed/reemitted etc, then it will take every route ...[text shortened]... outes that lead to that outcome, combined with the wave function of the photon along each route.
I don't believe the act of looking at a cat can determines its state, the act of looking only tells me which state is actually true. But the act of looking at something on the quantum level actually can and does influence what is being looked at, simply because of what it takes to observe something as small as quanta.
27 Jul 13
Originally posted by lemon limeThe probability of the photon ending up in a particular place (when it finally interacts in an 'observable' way) depends on all the possible routes to get there. However there is a cyclic (wave like) property to the photons probability, thus some paths interact with other paths in such a way that they cancel out rather than adding. So for example in the two slit experiment, if the photon could go through either slit, there are some places where it is highly probable that it will hit the screen, and other places where it is highly improbable that it will hit the screen because the distances of the two routes are such that the probability vectors cancel out. So its not as simple as just adding up every route.
This is where I always run into trouble, because I'm never sure what is meant by every possible route. Does a photon really take every possible route, or must we assume every possible route is taken because we don't know (or can't know) which route is taken by the photon?
Any photon seems to be 'aware' of every route it could take. In the two slit experiment if you send one photon through a given slit one at a time you do not get an interference pattern, or if you find a way to detect which slit it went through you do not get an interference pattern.
Quantum mechanics is not intuitive, we need to just learn to accept that instead of always fighting with it to try and make it intuitive.
27 Jul 13
Originally posted by twhiteheadIt appears there is no avoiding confrontaion here or at any other thread. I'm not sure what you and few others here mean by intuitive, but I suspect it's being used as a default whenever you think someone is guessing or relying on a feeling.
Quantum mechanics is not intuitive, we need to just learn to accept that instead of always fighting with it to try and make it intuitive.
Just to illustrate what I mean, I could say a belief in evolution is intuitive in light of how little evidence there is to support it. You of course would disagree and claim evolution is a fact, when in fact the best you could actually say about it is that it's a viable scientific theory supported by a consensus. I would then argue with the word 'viable' and point out how using consensus as a support only weakens your position, because relying on a consensus is highly intuitive and a very poor substitute for evidence.
I think you or anyone would immediately see the problem of consensus determining whether or not something could be a fact if it was being used to support the notion of say, muscular fairys holding up the earth so it won't fall into who knows what, maybe fall into a black hole or something like that. My point is if you use something as a proof that only works for you because you want it to, but it won't work for something you know is false, then using it at all does nothing but show you are arguing from a weak position with heavy reliance on appearances. In other words, if your supporting evidence appears to be weak (acknowledging validity only if supporting what you believe) then it probably is weak, and can only work to throw suspicion on the very theory you are wishing to support.
Instead of saying all this, I suppose I could have started using the word intuitive to suggest you and few others here are simply guessing and making judgements according to your own personal feelings. But playing the same game back just to make a point never seems to accomplish anything, because people rarely see in themselves the same mistakes they see in others.
Originally posted by lemon lime
It appears there is no avoiding confrontaion here or at any other thread. I'm not sure what you and few others here mean by intuitive, but I suspect it's being used as a default whenever you think someone is guessing or relying on a feeling.
Just to illustrate what I mean, I could say a belief in evolution is intuitive in light of how lit h anything, because people rarely see in themselves the same mistakes they see in others.
I could say a belief in evolution is intuitive in light of how little evidence there is to support it.
You can say evolution is intuitive in light of how MUCH evidence there is to support it -the two not being mutually exclusive.
I could show you the many websites that show the vast amount of evidence that proves evolution -but I won't because; Did that; Been there before; Already know what the stupid response will be.
27 Jul 13
Originally posted by lemon limeI am in no way trying to be confrontational. I find quantum mechanics interesting, but am no expert and would like to learn more. I find discussing it helps me to understand it better.
It appears there is no avoiding confrontaion here or at any other thread. I'm not sure what you and few others here mean by intuitive, but I suspect it's being used as a default whenever you think someone is guessing or relying on a feeling.
I said 'we' need to stop fighting it, not 'you'. Nobody finds quantum mechanics intuitive.
By 'not intuitive', I mean that we always want to try and map the micro world of quantum mechanics onto a model that we can visualize in the macro world. So we want to see the photon as a particle moving from A to B. But a photon isn't a particle that moves from A to B as a football would move. There simply is no perfect analogy in the macro world that can be used to explain how a photon does get from A to B. And I think we all find this deeply unsettling and we try our best to keep looking for a macro world analogy. I think the best solution however is to simply accept that there isn't one.
So a photon does not take every possible path from A to B. The photon gets from A to B, taking into account every possible path. How it gets from A to B is quantum mechanics. It can be calculated using equations. It has some aspects that look like a football, and some aspects that look like a wave, but neither is an exact match.
28 Jul 13
Originally posted by lemon limeIn the context of physics words like intuitive and natural take on slightly different meanings. Intuitively a fluid in the bottom of an upright test-tube can't overcome the gravitational potential barrier and flow out of the test-tube. Cool helium down below it's super-fluid transition point and it will do that (this is a nice demonstration, part of a BBC documentary on YouTube: ). This is a clearly counter-intuitive behaviour. However within the context of quantum theory one develops an intuition, so counter-intuitive can mean strange even by quantum mechanics standards.
It appears there is no avoiding confrontaion here or at any other thread. I'm not sure what you and few others here mean by intuitive, but I suspect it's being used as a default whenever you think someone is guessing or relying on a feeling.
Just to illustrate what I mean, I could say a belief in evolution is intuitive in light of how lit ...[text shortened]... h anything, because people rarely see in themselves the same mistakes they see in others.
Naturalness is a condition which essentially says that a theory should not require its parameters to be ultra-fine-tuned to get the universe we see. An unnatural theory in physics is one that creationists might become excited about as it makes us less likely to have come about naturally.
29 Jul 13
Originally posted by lemon limeI am actually curious as to what you mean here. Would you care to start a thread on the topic? What specifically about evolution do you think has little supporting evidence? As a general statement it seems blatantly false, so you must be talking about some specific aspect of evolution and I would like to know what (but in a new thread please to avoid confusion with photons).
Just to illustrate what I mean, I could say a belief in evolution is intuitive in light of how little evidence there is to support it.
29 Jul 13
This is my understanding of how to work out the probability of a photon getting from A to B.
1. Draw a clock on the photon, with just one hand of unit length.
2. Rotate the hand at the frequency of the photon.
3. Follow the photon down every possible path from A to B, noting the position of the hand each time at B.
4. Add up the clock hands of all possible hands using vector addition.
5. The magnitude of the resulting vector is the probability of the photon getting from A to B.
Someone please correct me if I have got that wrong, especially 4. and 5.
Its interesting to note that a photon that is absorbed and re-emitted by an electron enroute seems to remember where its clock hand was. ie the emitted photon has the same phase as the absorbed one. I am not sure if it moves on during the time delay or is re-emitted as if no time had passed. Comments anyone?