Do photons travel back in time in the presence of gravitational fields?

[Hypercube]

I recently thought of something; since photons travel at the speed of light they are moving 0% through time (very crudely put, I know). So what would happen if they came in contact with a powerful gravitational field? Since gravity causes time to slow down as well as velocity, wouldn't that mean that photons would travel back in time? Since they'd be moving through time slower than not at all.

[thedarkshade]

According to relativity if you travel faster than light the order of events begins to reverse, not at c. Put roughly, c is kinda neutral.

[iNow]

That doesn't seem to answer the question in the OP, shade.

 

Hypercube,

 

You are mixing reference frames. The photon, if it could be said to have it's own reference frame, from that reference fream moves "0% through time" as you put it.

 

However, when the light interacts with gravity and is time dilated, that is only relative to some other / external reference frame.

 

So, the answer is no. A photon interacting with gravity will not travel back in time.

[Blue Fire]

[snip]

However, when the light interacts with gravity and is time dilated, that is only relative to some other / external reference frame.

 

So, the answer is no. A photon interacting with gravity will not travel back in time.

How is light time dilated by gravity? My understanding is that a photon always travels at c regardless of one's frame of reference - anyone in any reference frame will always measure the speed of light to be c, if the light isn't impeded by some medium (see below). A photon passing close to a black hole is not slowed down - it's path will be severely bent according to the curvature of space caused by the extreme gravity of the black hole but it's velocity won't change. Light will, of course, slow down inside some medium it is passing through (like glass) but that is because the individual photons are getting absorbed and re-emitted continually.

 

Is my understanding flawed?

[iNow]

Blue fire,

 

You may very well be right. My primary point was that a) the OP was mixing reference frames, and b) the photon is not travelling back in time.

 

After that, I'm not certain. Sorry for my lack on understanding on the question you posed. You are quite right that c is constant in all frames...

[ajb]

Are we talking about QED on a curved space-time or just classical electromagnetism?

 

If we are talking about QED on a curved space-time then when the curvature becomes comparable to the Compton wavelength of an electron we have some interesting effects, viz light can travel faster than c.

[Farsight]

I recently thought of something; since photons travel at the speed of light they are moving 0% through time (very crudely put, I know). So what would happen if they came in contact with a powerful gravitational field? Since gravity causes time to slow down as well as velocity, wouldn't that mean that photons would travel back in time? Since they'd be moving through time slower than not at all.

Photons move through space. No time "passes" for a photon. Gravity doesn't cause time to slow down. It causes photons to slow down. And we mark our time from the motion of light. Nothing more. Note that photons do not "move through time". Neither backwards, nor forward. It's just a figure of speech, like "clocks run" and "time passes". They move through space. And that's why time travel is impossible.

[Zephir]

..Gravity doesn't cause time to slow down. It causes photons to slow down.....

Farsight, such stance depends on the observational perspective used and this can be always dual. You can build working theory based upon concept of time dilatation by the same way, like upon concept of light slowing with the same results.

 

 

For example, the gravitational lensing can be interpreted as a result of space-time curvature under constant speed of light by the very same way, like it can be interpreted as a result of variable speed of light inside of invariant space-time.

[ydoaPs]

Photons move through space. No time "passes" for a photon. Gravity doesn't cause time to slow down. It causes photons to slow down. And we mark our time from the motion of light. Nothing more. Note that photons do not "move through time". Neither backwards, nor forward. It's just a figure of speech, like "clocks run" and "time passes". They move through space. And that's why time travel is impossible.

 

Photons don't slow down. They're either travelling at c, or they are absorbed.

[swansont]

Before this goes too far, a reminder that this is in the physics section. Answers to this question needs to be based in and consistent with relativity. Any alternative explanation belongs in speculations.

[Zephir]

... Answers to this question needs to be based in and consistent with relativity. Any alternative explanation belongs in speculations...

While the Farshight's answer was consistent rather with quantum mechanics, instead...;-) Is it correct, after then - or should he be crucified anyway?

[ajb]

While the Farshight's answer was consistent rather with quantum mechanics, instead...;-) Is it correct, after then - or should he be crucified anyway?

 

Leave it out Zephir.

 

We like to work within the set (category?) of accepted physics.

 

You can of course push this, but only in a consistent way. Unless you can do this use another forum or post in the speculation section.

[Zephir]

...you can of course push this, but only in a consistent way..

Accepted by who? What prohibit us to consider the quantum chaos and uncertainty as a result of local Lorentz symmetry/invariance violation? Can you refute such perspective by consistent way?

[ajb]

What prohibit us to consider the quantum chaos and uncertainty as a result of local Lorentz symmetry/invariance violation? Can you refute such perspective by consistent way?

 

Please do so...

 

 

Lorentz violation is interesting. Please formulate your ideas so we can understand and make comments.

[swansont]

Accepted by who? What prohibit us to consider the quantum chaos and uncertainty as a result of local Lorentz symmetry/invariance violation? Can you refute such perspective by consistent way?

 

 

Please do so...

 

 

Lorentz violation is interesting. Please formulate your ideas so we can understand and make comments.

 

But do so in an appropriate area. Don't hijack a thread on a different topic.

 

new topic = new thread

 

not established physics = speculations

 

edit: OT and speculative material has been, and will continue to be moved to the appropriate areas.

[Zephir]

OT and speculative material has been, and will continue to be moved to the appropriate areas.

OK - this is full right of yours, but please consider, every post of mine is archived and it can be used as an evidence of forum admin trolling later. It's good to know for society, who is playing the role of retarded inquisition after Galileo times, as it can spice the CV of such person and it will make the behavior of such people more responsible.

 

Lord Kelvin (1895): "Heavier than air flying machines are impossible".

[YT2095]

Lord Kelvin (1895): "Heavier than air flying machines are impossible".

 

They still are!

[swansont]

OK - this is full right of yours, but please consider, every post of mine is archived and it can be used as an evidence of forum admin trolling later. It's good to know for society, who is playing the role of retarded inquisition after Galileo times, as it can spice the CV of such person and it will make the behavior of such people more responsible.

 

The device has yet to be invented, that could measure how little this matters to me, and I suspect, other mods/admins.

 

If posts are off-topic, they are subject to being moved to a new thread.

If posts lack reasonable experimental and/or theoretical support, they are subject to being moved to speculations.

 

You are not being singled out for this — it applies to everyone.