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The Gravity of a Photon

jwkennington.com

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Re: The Gravity of a Photon

#81

Post by kgwgk »

JadeNB wrote: post #77
kgwgk wrote: post #40

Earlier quoted context omitted.

That links says: “Unsolved problem in physics: Are the three forces of the Standard Model unified at high energies?” But we may be close, for some values of close :-)

> That links says: “Unsolved problem in physics: Are the three forces of the Standard Model unified at high energies?” Indeed, that's why I said only that there were theories about it.

Sure, but the solutions to the solved problems in physics are also called "theories". I'm sure you knew the GUT is not yet done, it was just a clarification.

Re: The Gravity of a Photon

#82

Post by kgwgk »

danbruc wrote: post #38
Causality1 wrote: post #32

What I've always found wild about gravity and photons is that gravity produces the same proportionate effect, i.e., acceleration, on them as it does normal matter and the only reason the sun and planets don't render light nearly unusable for sensing by utterly distorting the light's path is that it travels so quickly it doesn't spend any significant amount of time in a gravity well. I don't think I'll ever fully wrap…

That is an interesting thought that never occured to me. It would render the headlights of your car pretty much useless if the light just fell to the ground a few meters in front of the car. I wonder if one has or could measure the effect in the lab - it's about 0.5 μm over a distance of 100 km, so it seems not totally out of reach.

Your comment reminded me of Gamow's Mr. Tompkins in Wonderland. I don't know if he mentioned that in particular, but he discussed what relativistic effects would look like if the speed of light was 10 MPH.

http://www.arvindguptatoys.com/arvindgupta/tompkins.pdf

Re: The Gravity of a Photon

#83

Post by JadeNB »

kgwgk wrote: post #81
JadeNB wrote: post #77

Earlier quoted context omitted.

> That links says: “Unsolved problem in physics: Are the three forces of the Standard Model unified at high energies?” Indeed, that's why I said only that there were theories about it.

Sure, but the solutions to the solved problems in physics are also called "theories". I'm sure you knew the GUT is not yet done, it was just a clarification.

I always appreciate non-shouty clarifications of misunderstandings, combined with charitable interpretations of others' motives and knowledge. Thank you!

Re: The Gravity of a Photon

#84

Post by danbruc »

kgwgk wrote: post #82
danbruc wrote: post #38

Earlier quoted context omitted.

That is an interesting thought that never occured to me. It would render the headlights of your car pretty much useless if the light just fell to the ground a few meters in front of the car. I wonder if one has or could measure the effect in the lab - it's about 0.5 μm over a distance of 100 km, so it seems not totally out of reach.

Your comment reminded me of Gamow's Mr. Tompkins in Wonderland. I don't know if he mentioned that in particular, but he discussed what relativistic effects would look like if the speed of light was 10 MPH. http://www.arvindguptatoys.com/arvindgupta/tompkins.pdf

There is also a free game, A Slower Speed of Light. [1]

[1] http://gamelab.mit.edu/games/a-slower-speed-of-light/

Re: The Gravity of a Photon

#85

Post by Causality1 »

danbruc wrote: post #79
Causality1 wrote: post #73

Earlier quoted context omitted.

It's a bit tricky because it isn't light taking a curved path through your lab; it's light taking a straight path through the curved spacetime in your lab.

The elevator thought experiment suggests that the light will indeed also take a curved path through my lab, but I am way out of the territory where I have any good intuition. And I have no intuition at all what would happen to the matter the elevator is made of if one accelerated it hard enough to make the effect noticable, nor do I have any idea what Earth's gravity does to matter in my lab. Can I have a trully stra…

If you had a 100km long rod that was perfectly, impossibly straight and infinitely strong, placing it in a gravity well equal to that at the earth's surface would still make it look bent by half a micrometer to an outside observer, in the same way you can draw a triangle on a sphere using nothing but three right angles and three straight lines.

If that's not interesting enough, do some reading on the relative nature of spontaneity. Two things that happen at exactly the same time in one reference frame don't happen at the same time in another. Crazy.

Re: The Gravity of a Photon

#86

Post by danbruc »

Causality1 wrote: post #85
danbruc wrote: post #79

Earlier quoted context omitted.

The elevator thought experiment suggests that the light will indeed also take a curved path through my lab, but I am way out of the territory where I have any good intuition. And I have no intuition at all what would happen to the matter the elevator is made of if one accelerated it hard enough to make the effect noticable, nor do I have any idea what Earth's gravity does to matter in my lab. Can I have a trully stra…

If you had a 100km long rod that was perfectly, impossibly straight and infinitely strong, placing it in a gravity well equal to that at the earth's surface would still make it look bent by half a micrometer to an outside observer, in the same way you can draw a triangle on a sphere using nothing but three right angles and three straight lines. If that's not interesting enough, do some reading on the relative nature…

I guess this is an autocorrect issue, but you certainly mean simultaneity. Anyway, I have been through several university courses on special and general relativity with all the math and have at least some basic understanding of the thing. However, as said before, I have no real intuition for it.

So the only thing I can work from right now is the elevator thought experiment and it seems to me that I can have a perfectly straight rod in a 100 km wide elevator accelerating at 9.81 m/s² while a light ray would bend downwards by 0.5 µm. So ignoring the fact that Earth's gravitational field is not uniform, this seems to suggest that even a rod made out of some common material would not be bend or appear bend or whatever in Earth's gravitational field. Maybe this analogy just leaves the realm of validity of the thought experiment, but I honestly don't know.

I am also not convinced by your analogy with the triangle on a sphere, gravity is curvature of spacetime but the analogy involves only curvature of space. If you tell me that you are a physicist specialized in general relativity, I will take your word for it, otherwise I will keep some doubt about getting my nice rod bend in the same way the light path gets bend, after all they are two quite different things, an extended object versus a path through spacetime.

Re: The Gravity of a Photon

#87

Post by noobermin »

filmor wrote: post #62
danbruc wrote: post #14

Earlier quoted context omitted.

The warm box will of course »heavier« because it contains additional energy. Fundamentally there is no mass, it is just a convenient way to talk about the energy hidden in the structure of matter.

The internal structure of leptons being? :)

This isn't quite the same thing as what adds mass to say hadrons like who you're replying to is, but at least according to the Standard Model, leptons as well as quarks start out massless and acquire an inertial mass due to interaction with the Higgs field. You wouldn't say it is "internal structure" but it arises due to interactions rather than being an a-priori property.

Re: The Gravity of a Photon

#88

Post by Sharlin »

Ceezy wrote: post #49

I don t understand. The title is gravity of photon. Then you start talking about electromagnetic field. I sure something is missing here. What would be the source of gravitation and who is subject to that field?

Photons are excitations of the electromagnetic field. The source of gravity is the energy in the EM field, as described by general relativity.

Re: The Gravity of a Photon

#89

Post by tsimionescu »

danbruc wrote: post #27
tsimionescu wrote: post #22

Earlier quoted context omitted.

Honest question: aren't radio waves "physical objects" that represent oscillations of an electro-magnetic field, to the best of our current understanding?

Radio waves are streams of photons, the fields are just a mathematical tool we use to describe this. And there are several of them, the classical electromagnetic field but also an entire set of fields involved in the quantum version.

My understanding was that some kind of wave-particle dualism was well accepted. It's exact physical meaning may not be understood, but isn't there experimental evidence that photons, even individual ones, behave as waves in some circumstances (as does as any other 'particle', in fact)?

I've seen this dualism claimed pretty recently by Leonard Susskind.

Re: The Gravity of a Photon

#90

Post by tsimionescu »

dschuetz wrote: post #26
tsimionescu wrote: post #22

Earlier quoted context omitted.

Honest question: aren't radio waves "physical objects" that represent oscillations of an electro-magnetic field, to the best of our current understanding?

There is an agreement in physics that low energy EM fields are called waves, such as radio waves, and high energy EM fields are called photons or even particles. In any case they are actually both. If they are physical objects I don't know. I think, I wouldn't go that far.

Sure, they are both, but my point was - if they have wave-like characteristics, they must be a wave of/in something; if we can have experimental evidence that the wave exists, I would consider that experimental evidence that the field the wave is a wave of must also exist, to the same extent.
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