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nnerik
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If a photon does not experience time, how can it change? Without change, how can it have frequency?
nnerik said:If a photon does not experience time, how can it change? Without change, how can it have frequency?
What do you mean by this?phinds said:"Photon" is what we call the result when a light beam hits an object. Light does not travel as photons and photons are not particles in the classic sense, they are quantum objects. Light does not HAVE a perspective or an experience.
The change and frequency are descriptions of the photon from our human perspective. Physics describes what we can observe, not what photons can observe.nnerik said:If a photon does not experience time, how can it change? Without change, how can it have frequency?
OK, I stand corrected. Thanks. I try to get people to avoid thinking about light propagating as photons because it conjures up images of little tiny balls traveling along and that's not helpful.nasu said:What do you mean by this?
True, there are models where you can describe light propagation without using photons, like classical electromagnetism.
But the QED describes propagation and the other phenomena related to light and electrons in terms of photons, doesn't it?
How would you test the fact that is does not propagate as photons?
The single photon sources and detectors exist. How does light propagates in the case of a single photon source?
At the beginning of quantum physics, many physicists, including Plank, liked to think that photons are just some artifact of the interaction between light and matter.
But I think that the modern theories accept the existence of photons.
I understand that many times it is appropriate to tell the poster struggling with understanding light to forget about photons and stay with Maxwell's theory.
But this is not because photons do not "exist" in the most complete theories we have now.
phinds said:OK, I stand corrected. Thanks. I try to get people to avoid thinking about light propagating as photons because it conjures up images of little tiny balls traveling along and that's not helpful.
ZapperZ said:Here's the problem with your question.
In saying "a photon does not experience time", you have explicitly used the concept of Special Relativity (unless you came up with your own personal theory). SR has a set of postulates, which are the starting points of that theory. One of the postulates stated that light has a constant speed in any inertial reference frame. Only then, can you derive all the equations from SR, including the "time dilation" equation which you had used to somehow arrive at your conclusion that a photon does not experience time.
nnerik said:Not really. My point is that the photon will have to "swing" n periods in zero proper time. That is an infinite "proper frequency", isn't it? This works fine in a spacetime diagram, but that is only because you are allowed to draw lines between points with zero separation!
How can anything "happen" between A and B when the invariant "distance" is zero? Don't you agree that this is at least a little bit puzzling?
ZapperZ said:You still don't get it.
Where do all these concepts of "proper time" and "proper length" and "invariant distance is zero" came from? From your dreams?
I got as far as that first reference and found "From the perspective of a photon..." which indicates that he doesn't know what he's talking about. I would not be surprised if the rest are equally pop-science misinformation. These kinds of things can be fun to read and can get you thinking about things, but they are not to be trusted for the actual science.nnerik said:Not dreams, mostly from books, articles and lectures. A few accessible references:
http://www.universetoday.com/111603/does-light-experience-time/
This is a good time to remind everyone of the Physics Forums policy on acceptable sources - none of these are valid references.nnerik said:Not dreams, mostly from books, articles and lectures. A few accessible references:
http://www.universetoday.com/111603/does-light-experience-time/
https://www.quora.com/Does-a-photon-experience-time
https://medium.com/starts-with-a-bang/ask-ethan-109-how-do-photons-experience-time-94756eab8bf9
https://quantumweird.wordpress.com/2007/06/23/does-time-exist/
You think it funny, and I can understand that, but you need to realize that we get very frustrated here by people asking questions based on crap science (and this happens over and over) so we don't see the humor in it after about the 10th time, to say nothing of the 100th, and this post is approximately the 25,000th (possibly more). We don't MIND, because dispelling such misconceptions is part of the point of the forum, I'm just saying we don't see it as humorous.nnerik said:God forbid! Best not to check! Pop-science is one thing, but what if you came across some real rock'n roll-science? Say, cyclic cosmology, or **** like that!
Nugatory said:The proper time, proper distance, and invariant intervals that you mention in your post #8 above are all the results of a chain of logic that starts with an assumption (essentially, one of the postulates of relativity) that there is no frame in which light is at rest. Therefore any attempt to use these concepts to understand a frame in which light is at rest is starting with inconsistent premises, and there is no reason to trust the conclusions you draw from them.
Because they're two different points. Imagine a photodetector wired up to an explosive device, and consider the two events "Someone standing 100 meters away from the bomb uses a laser pointer to illuminate the photodetector" and "the light reaches the photodetector and sets off the bomb". Those two events are separated by a lightlike interval of length zero, but it makes a big difference whether your worldline passes through one or the other. One way you're shaking someone's hand and saying "nice fireworks"; the other way you're blown to bits.Why can't we think of all events on a light-like interval as a single point/event?
Mathematically, you can choose an affine parameter other than proper time to label the points on a lightlike curve. That allows you to compute the different intensity of the electromagnetic field at different points on the curve (they are different points - see above). However, if you're thinking specifically about the frequency of a photon, the simplest answer is that "frequency" is the name that we attach to a property of photons defined by ##\nu=E/h## and which has dimensions of inverse time - the assumption that anything except the electromagnetic field is oscillating is unnecessary.nnerik said:My philosophical question is what would be the most intuitive way to understand how something can "change" along an interval that measures zero!
Demystifier said:The change and frequency are descriptions of the photon from our human perspective. Physics describes what we can observe, not what photons can observe.
When you speak of "the perspective of X", that is a convenient shorthand way of saying "from the perspective of an observer colocated with and at rest relative to X". Such observers can exist (at least in principle) if X is a massive particle but not if X is massless.nnerik said:But this should not prevent us from trying to understand the world from a photons perspective. If we can understand a massive particle's perspective, why not a massless particle's?
You are going to have to come up with your own definition of "perspective" in that case, since as has been pointed out repeatedly in this thread, the way you are using it now does not make any sense.nnerik said:But this should not prevent us from trying to understand the world from a photons perspective. If we can understand a massive particle's perspective, why not a massless particle's? It is often fruitful to try to see things from different perspectives.
Same reason that prevents us from "understanding" the charge of charge-less particles. :)nnerik said:But this should not prevent us from trying to understand the world from a photons perspective. If we can understand a massive particle's perspective, why not a massless particle's? It is often fruitful to try to see things from different perspectives.
Nugatory said:When you speak of "the perspective of X", that is a convenient shorthand way of saying "from the perspective of an observer colocated with and at rest relative to X". Such observers can exist (at least in principle) if X is a massive particle but not if X is massless.
nnerik said:Fair enough, which should imply that unless you are clueless, you would mean something slightly different when the particle is massless. Refer Roger Penrose's reference to the photon's perspective in the Youtube video I linked in a previous post.
https://www.youtube.com/watch?v=npmDbbGbSoE&feature=youtu.be&t=2571
nnerik said:Fair enough, which should imply that unless you are clueless, you would mean something slightly different when the particle is massless. Refer Roger Penrose's reference to the photon's perspective in the Youtube video I linked in a previous post.
One thing that might help is to consider the Doppler effect.nnerik said:If a photon does not experience time, how can it change? Without change, how can it have frequency?
That is true. But then one should not have prejudices that massless particle's perspective should be very similar to the massive particle's perspective. From a massive particle's perspective the spacetime can be split into 3-dimensional space and 1-dimensional time, but in a sense this is not so from a massless particle's perspective. Instead, for photons, the spacetime splits into a 2-dimensional space and two 1-dimensional null-coordinates.nnerik said:But this should not prevent us from trying to understand the world from a photons perspective. If we can understand a massive particle's perspective, why not a massless particle's? It is often fruitful to try to see things from different perspectives.
The frequency of a photon is a measure of how many times it oscillates per second. It is also referred to as the number of wave cycles per second.
The frequency of a photon is directly proportional to its energy. This means that the higher the frequency, the higher the energy of the photon.
Yes, a photon's frequency can change. This can happen when a photon interacts with matter, such as when it is absorbed or emitted by an atom.
Frequency and wavelength are inversely proportional for a photon. This means that as the frequency increases, the wavelength decreases, and vice versa.
The color of light emitted by a photon is determined by its frequency. Higher frequency photons appear as blue or violet light, while lower frequency photons appear as red or orange light.