Photons have no time

[InfiniteNow]

I've been trying to read more and more about QM. Last night, I read that photons do not experience time. That a photon travelling through time (relative to an observer in inertial frame) is indistinguishable from an anti-photon travelling backward in time. Strangely, I'm okay with that.

 

However, I'm struggling to understand that a photon released from a star 10 million light years away, from the perspective of something else, will take 10 million light years to arrive, but in it's own frame of reference arrives immediately to all places.

 

Can someone help shed some light ( :phones: ), and potentially assist me in clearing up mistakes in the above description? It sounds a lot like a photon is InfiniteNow, but I am trying to be objective. :evil:

[cwes99_03]

Well, you've reached the tip of the head of the confusion of GR. That light as a wave always propogates at a speed of c, and that photons must obey the same basic rule and that means it must travel at c irregardless of frame of reference. Thus a photon must be "unstuck in time" and yet traveling through space, or is it what defines space-time? AHHHHHHHHH!

[Jay-qu]

Time dilation increases as speed increases - max time dilation (ie no time at all) occurs at c, but normal matter cant get there, since photons are travel at c they have no time.

[TheFaithfulStone]

Okay, that's confusing. Wouldn't that mean that all photons share a reference frame at all times?

 

Wait NO - because they don't always travel at c do they? Does a photon have mass when it passes through water or air or whatever? Does it experience time then?

 

Also, if you have an area of negative pressure (Casimir Vacuum) and you sent a photon throught it, theoretically it would travel faster the c - then it would it be going backward in time, and arrive before it left?

 

Wacky stuff - and I'm just as confused as you.

 

On the other hand, it does sort of address my question about what reference frame quantum entanglement would occur in.

 

Interesting though - it almost leads to a redefinition of simultaneous. I have a photon, emitted from star A 10 years ago, and a photon emitted from star B 5 years ago - when I find them, I trap them. Which photon travelled longer? Neither - they where both trapped at the same time. If I release a photon from my "photon gun" toward Alpha Centauri and another toward the Mars, fifty minutes later, my counterpart on Mars can see my photon. Four years later Alpha Centauri catches my photon. Which photon was capture first? According the photon, they were both captured at the same time. Intuitively (ie, wrongly) every event that has ever happened to any photon not travelling through a gravity distorted frame or medium thicker than vacuum occured at the exact same instant throughtout the history of the universe.

 

Is time itself (the difference in this instant) the effect of mass and particles on the movement of photons?

 

Someone stop me before I make a complete *** of myself.

 

TFS

[too late, isn't it?]

 

Never mind - the gravity question is moot - it isn't curving because it's slowing down, it's curving because the definition of "straight line" has been changed. Hold for things like water though. Unless I misunderstand photon passage through water (quite likely.)

[infamous]

Time dilation increases as speed increases - max time dilation (ie no time at all) occurs at c, but normal matter cant get there, since photons are travel at c they have no time.

This fact is the very reason I'm a determinist; The photon has, according to it's perception, already reached it's final destination, locking in all of the previously occurred events.

 

Time is an illusion we humans falsely judge as the unfolding of events which in truth, according to the experience of the photon, has already occured. We can't change what the photon has already experienced, to do so would change the final state of the photon and would result in a paradox of reality.

 

Ask the photon; All events are predestined, the future is cast in stone. BTW, this is one scientific position which fits rather nicely with my religious point of view. Restraining myself, I will not delve into my reasons for this understanding, because to do so would be off topic. Just my humble opinion................Infy

[Qfwfq]

The difficulty is that the Lorentz coordinate transformations are singular in the v --> c limit, so it's a thorny problem to relate things for the two "observers".

 

Also, if you have an area of negative pressure (Casimir Vacuum) and you sent a photon throught it, theoretically it would travel faster the c - then it would it be going backward in time, and arrive before it left?

How do you get that concluson? :eek2: The Casimir effect involves the inner region having a lower pressure than the outer region. I don't see this implying v > c.

[hallenrm]

Ah!! it all adds up to only one conclusion, no theory is ever perfect, No one, whether it was Einstein or any body else has discovered the ultimate truth, because there cannot be any ultimate truth. We can approach it, just as the question posed by Infinitenow indicates v -> c but never reach it.

 

:eek2: :lol: :eek: :wave: :lol:

[cwes99_03]

Ok so negative pressure was explained well enough. Photons do not travel at speeds other than c. Refraction of light causes light to be absorbed and re-emitted in the medium it is traveling through, and thus due to absorption and re-emision times the light is perceived by us to travel at v<c.

The actual thought that I believe is missing here is that time is not defined for c because there is no inertial reference frame for c (for time to be calculated one must have an inertial reference frame). That being said, it is not that the light has not been traveling from star b for 5 less years than from star a, but that the time traveled cannot be defined by a referential frame of light (because it does not exist.) It therefore must be defined by a frame of reference that does exist.

 

i.e. if you were capable of traveling at the speed of light, time would cease to exist for you. Thus the photon cannot degrade by traveling from point a to point b. It can only degrade (lose power) if it interacts with matter.

 

Thus is the cunundrum for many of us. That is to say that travel at or above light speed is impossible for anything with mass (and something with mass is the only thing that might have the ability to measure time). That is why, to test theories of SR an extremely low mass particle with a predictable time of degradation is observed. It cannot travel at c, but relatively close to it, and time dilation can be more easily calculated for speeds near c (reason, a bigger window of observation).

[Qfwfq]

The actual thought that I believe is missing here is that time is not defined for c because there is no inertial reference frame for c (for time to be calculated one must have an inertial reference frame).

It wasn't quite totally missing, it's an alternative way of saying "the Lorentz coordinate transformations are singular in the v --> c limit".

[TheFaithfulStone]

How do you get that concluson? The Casimir effect involves the inner region having a lower pressure than the outer region. I don't see this implying v > c.

 

Read it here - for that other thread.

http://en.wikipedia.org/wiki/Faster_than_light Of course, they don't say what the calculations ARE...

 

Here it is again. Certaintly speculative, but I didn't just totally pull it out of my rump.

http://en.wikipedia.org/wiki/Scharnhorst_Effect

 

There is some stuff on arXiv about it, but I don't know what "birefringent" means, so...

 

It does kind of imply an luminferous-ether-kinda-thing doesn't it?

 

What about all these "slow light" experiments I've been reading about? Just changing the defraction of gas to something really high?

 

TFS

[cwes99_03]

Perhaps you can look into this from

http://www.altair.org/labnotes_EmagDNG.html

 

In recent years, Composite MetaMaterials "CMMs" have inspired great interest due to their unique physical properties and novel applications of these materials. [1,2] Two important parameters, electrical permittivity ε and magnetic permeability µ, determine the response of the material to the electromagnetic radiation. Generally, ε and µ are both positive in ordinary materials. While ε could be negative in ordinary materials (for instance in metals), no natural materials with negative mare known. However, for certain structures which are called left-handed materials (LHM), both the effective permittivity εeff and permeability µeff possess negative values. In such materials the index of refraction is less than zero, and therefore, phase and group velocity of an electromagnetic (EM) wave can propagate in opposite directions. This behavior leads to a number of interesting properties. [3] The phenomena of negative index of refraction was first theoretically proposed by Veselago in 1968. [4] Veselago also investigated various interesting optical properties of the negative index structures.

 

http://www.fen.bilkent.edu.tr/~ozbay/Papers/70-03-ieee-ozbay_tap_2003.pdf http://www.photonics.com/spectra/tech/XQ/ASP/techid.848/QX/read.htm http://ceta-p5.mit.edu/metamaterials/papers/external/2004/Krowne_prl_2004.pdf http://ceta-p5.mit.edu/metamaterials/papers/external/2000/smith.K_prl_2000.pdf http://www.fen.bilkent.edu.tr/~ozbay/Papers/70-03-ieee-ozbay_tap_2003.pdf

 

Otherwise the only occasion which i have come across which shows a n<1 material (which would mean that light travels at v>c in that material) is when people are talking about ULIMs which I know next to nothing about. Perhaps some research on your and my part is in order.

 

http://oemagazine.com/fromthemagazine/jan05/pdf/anewpath.pdf

[InfiniteNow]

Right... interesting conversation all. I guess the part with which I'm struggling is that if a photon has not time wouldn't it also not have space, since the two are inextricably linked? Is a "photon" really everywhere at all times?

 

Granted, trying to put my macroworld understanding into quantum ideas is not the best use of my resources, and I'll continue chasing my tail for a while until I get tired, but I would like to understand it better.

 

Photons don't have time. Things that make you go "hmmm," indeed. :hihi:

[cwes99_03]

I guess the simple answer to that is no. It does not have volume. It is a virtual particle. What you are trying to ask might be, is it possible for a photon to travel through space? Yes. Then I guess the next good question is if it is a Boson, namely does the Heisenberg uncertainty principle apply to it? If Heisenberg does, then you can't possibly know its exact position, though I suppose you can have a rough guess of it.

But since a photon does not have measureable mass, then the only way to measure it is by actually destroying it, I'd say it has a beginning and an end and a velocity, so yes, I'd say you can measure it's position relatively well.

 

Now having said that to make you do a bit more thinking about some things you might not have thought about, and since that's all i can think of with 20 minutes left in my work day, I'll leave you with this last thought.

 

In my limited understanding, c is what defines space-time and ties them together, or at least it plays a hugely significant role. A photon is really just a quantized measurement of light which is dependent upon the frequency of light being measured. The frequency of light depends upon the reference frame of the measuring device and not on the speed of light (which we hold to be constant). That is why regardless of the reference frame we hold all light to be traveling at c. Perhaps this is wrong (light only traveling at c, not having a frame of reference). I don't know, but i know without mass or volume, we can't measure the particle.

[Jay-qu]

Wait NO - because they don't always travel at c do they? Does a photon have mass when it passes through water or air or whatever? Does it experience time then?

 

It still travels at c even then. Its just because of constant particle interactions appear to slow it down, but infact it still travels at c between particles :friday:

[Qfwfq]

The wiki about the Scharnhorst effect says that it isn't expected to lead to causality problems, and my humble view is that it couldn't anyway, I think the traditional habit of calling c "the speed of light" leads even many a theoretical physicist into blunders, when reasoning on subtle matters. If only Einstein had realized that light isn't the emperor of space time! Minkowski adopted a better approach but his pupil became a much more charismatic figure.

[Qfwfq]

Then I guess the next good question is if it is a Boson, namely does the Heisenberg uncertainty principle apply to it?

Heisenberg certainly does apply to the photon, it applies to bosons as well as fermions. Are you perhaps confusing with Pauli's exclusion principle?

[cwes99_03]

Perhaps, that may be. It has been 4 years since my advanced thermo class.