Photons and Special Relativity

[Gerbus]

I have an intuitive question regarding photons.

I have been trying to form a good and unique paradigm over the last couple of months. When I think of relatively moving inertial frames, I picture an arbitrary object travelling through space, and when I tag along with the object (in my mind's eye), lengths and masses and times (of objects "stationary") are transformed accordingly. I find it attractive to think of each successive velocity that the object can shift to (via acceleration, but this is not important to the paradigm) in terms of the object shifting into a completely parallel universe, where everything is identical except for the contracted/dilated dimensions.

Now, thinking as above, I can't help but think of a photon. If (theoretically) we think of the photon as some mass that we have successfully accelerated up to v=c, then in the frame of the photon, everything "moving" past the photon has an infintely dilated time. So, can I think of the photon as existing within a single "quanta" of time? In this case, a photon would appear to have an infinite lifetime right?

I realize I'm probably mixing a lot of distinct ideas that perhaps should not be mixed, but how is my thinking on this topic?

Gerbus

[Bo]

hi and welcome! The most important step of your observations is correct, but you make some technical errors:

shifting into a completely parallel universe

so if i throw a ball, it shifts to a different universe? and while it slows down, it passes infinetely many universes? this is not the general concept of what a "universe" is, but (i think) i understand what you mean. (replace "universe" with "inertia frame"...)

contracted/dilated dimensions

A dimension isn't dilated ("do you know when the next dimension comes?" "yes it is 5 minutes late"). the corect statement is that the measure of a dimension (so e.g. the second, or the meter) increases or decreases (but as mentioned: these are technical points; your thoughts are correct)

everything "moving" past the photon has an infintely dilated time. So, can I think of the photon as existing within a single "quanta" of time? In this case, a photon would appear to have an infinite lifetime right?

The first statement is corect, in the other two statements you use terminology from quantum mechanics and particle physics, that simpy said aren't appropriate here.
The conclusion from the first statement is that from the photon's point of view, the deperture and arival from 2 pointsare at the same time. But from an external observer the photon exists for x/c (x = the distance between the 2 points) time. So you shouldn't think of the photon living in a single moment, since -by the very nature of the argument- time is relative. As mentioned above: the word quanta isn't appropriate here, since this argument doesn't use the quantised nature of time.

The last remark about lifetime is just not true: first of all the notion of lifetime is used when an unstable particle decays, by emission of some energy, to a more stable one. There simply is nothing the photon -in this way- can decay into. But since the photon IS a bunch of energy, it can 'decay' into matter (by the famous E=mc^2). For example a photon can decay in an electron-positron pair.

Bo

[Gerbus]

Okay, kewl. I guess I am thinking non relatively when I am thinking about how space and time appear to a photon. Thanks for clarifying.

In regards to mixing QT, GR, and Particle Physics, I am struggling to really get at the heart of why GR and QT are inconsitant. I have read the forums related to this seeming discrepancy, but all I am getting from such discussions is that GR is macroscopic and QT is microscopic. I understand that they are excellent and accurate in their respective scopes, but I guess I am wondering what exactly is needed to unite the two. Are unition efforts really just looking for a QT that when used on large scales actually becomes GR? I guess since QT ignores gravity for the most part, when viewed at large scales there is no gravity at all, and when GR is viewed at small scales, there are no forces whatsoever (since gravity becomes incredibly weak).

Also, if I do want to put myself in the "shoes" of a photon, instead of thinking that it exists in one "quanta" of time, can I think of it as existing completely independant of time? I am still having conceptual difficulties in putting myself in a photon's shoes. If I were a photon, I could still look at my watch and see it tick normally, but someone "at rest" would notice that my watch is not ticking at all, no matter how long they watch me. So to someone else, I really have no (passage of) time, but to me, everything in my frame seems normal.


As an aside, I am currently studying physics at UBC. This semester I am taking Cosmology, Elementary Particle Physics, and Quantum Physics. I'm very excited about all three of these courses.

Gerbus

[Tormod]

Originally Posted by Gerbus

I am struggling to really get at the heart of why GR and QT are inconsitant. I have read the forums related to this seeming discrepancy, but all I am getting from such discussions is that GR is macroscopic and QT is microscopic.

I am no expert on the matter but why would we need to unite the two? They describe (as you say) different things - GR is all about macroscopic objects and QT is about the sub-atomic particles and forces (not "microscopic" - these are still larger than atoms).

It's like combining novels and non-fiction - it doesn't make sense (okay, stupid analogy, sorry).

As an aside, I am currently studying physics at UBC. This semester I am taking Cosmology, Elementary Particle Physics, and Quantum Physics. I'm very excited about all three of these courses.

Sounds very exiting! In the end you will be the one explaining all this to us.

[lindagarrette]

I think theoretical physicists would like the unification so they can have a clear answer to the "what is gravity? question. It seems that at the quantum level the effect of gravity is neglible so in a sense, Tormon has a good point. Maybe there is no connection.

[infamous]

Originally Posted by lindagarrette

I think theoretical physicists would like the unification so they can have a clear answer to the "what is gravity? question. It seems that at the quantum level the effect of gravity is neglible so in a sense, Tormon has a good point. Maybe there is no connection.

Tormod may be exactly right on this one Linda, but I for one, can't resist the challenge to connect the dots!!!

[Gerbus]

I can't possibly accept that they don't need to be united. All of the progress in science over the past three thousand years has been in the form of steps towards uniting different aspects of the physical world under common laws. I quest, as most physicists do I'm sure, for the ultimate theory of everything. Of course, there is a philosophical part of me that is pretty sure this can't be achieved, but the quest remains. Even if we do find a Grand Unified Theory for everything physical, it probably (knock on wood) won't describe exactly what "love" or "consciousness" is. Nonetheless, I need to seek the theory of theories.

[maddog]

Originally Posted by Gerbus

I have an intuitive question regarding photons.

I have been trying to form a good and unique paradigm over the last couple of months. When I think of relatively moving inertial frames, I picture an arbitrary object travelling through space, and when I tag along with the object (in my mind's eye), lengths and masses and times (of objects "stationary") are transformed accordingly. I find it attractive to think of each successive velocity that the object can shift to (via acceleration, but this is not important to the paradigm) in terms of the object shifting into a completely parallel universe, where everything is identical except for the contracted/dilated dimensions.

Now, thinking as above, I can't help but think of a photon. If (theoretically) we think of the photon as some mass that we have successfully accelerated up to v=c, then in the frame of the photon, everything "moving" past the photon has an infintely dilated time. So, can I think of the photon as existing within a single "quanta" of time? In this case, a photon would appear to have an infinite lifetime right?

I realize I'm probably mixing a lot of distinct ideas that perhaps should not be mixed, but how is my thinking on this topic?

Gerbus

It was this thought problem in essence that Einstein came up with SR. As written in
biographies of him, that at 17, thinking of Maxwell's equations; he imagined ridding on a
beam light (previous to photons). This is how it was said it all started.

Yes, the notion of time stopping ("infinite dilation") is why it is thought there is no time
sense for a photon. In QED, all photonic/light interaction can be fully done independent of
time. I still find this odd.

Maddog

[Bo]

discussions is that GR is macroscopic and QT is microscopic. I understand that they are excellent and accurate in their respective scopes, but I guess I am wondering what exactly is needed to unite the two

In general it is true that GR is macroscopic in QT microscopic, however there are cases where the 2 theories mix. The most profound examples are black holes and the big bang.(key point of course is that the matter density is so high, that even on small scales gravitational effects are important) (or, since you study physics you might have heard these terms: The schwarzschild radius and the de broglie wavelength become comparable in size). So QT only effects small scales, but sometimes gravity also does.
To see what is needed to unify the 2, you first should know why they can't be unified. QT gives an excellent descriptionon how to calculate a quantum theory of gravity, however if you do this, all your observable quantities are infinite (in other words: nonsense)(in the literature this is called 'nonrenormalizable'). The heart of this problem lies in the fact that GR requires a completely smooth spacetime, while quantum uncertainty makes all kinds of bumps and spikes at the small scale in the structure of space time.
From this the solutiion of string theory (which is the only more or less consistent quantum gravity theory we know) also becomes clear: By giving the particles a length (instead of them just being a point), they get a little bit 'spread out' over the quantum bumps and spikes and thereby giving a net result that is more or less smooth (at least: smooth enough for GR)

As an aside, I am currently studying physics at UBC. This semester I am taking Cosmology, Elementary Particle Physics, and Quantum Physics. I'm very excited about all three of these courses.

that's the part where the real fun starts
Bo

[lindagarrette]

Thanks, Bo, wow a really good explanation. It's important for me to follow the theoretical physicists on this issue because everything ultimately is quantum. At that level there could indetermined events. You have to show me, though.