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Dadface
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Light can be affected by gravity and as I understand it light can be a source of gravitational effects on other objects. But have such effects been detected? References would be helpful.
Thank you
Thank you
UltrafastPED said:The Pound-Rebka experiment (1959) exploited the Mossbauer effect to verify the effect of gravity upon light:
http://en.wikipedia.org/wiki/Pound–Rebka_experiment
The effect of light upon gravity is very weak; light simply adds to the momentum flows and energy density. AFAIK there have been no proposed experiments to detect this.
You can read about all of the standard tests in Clifford M. Will's
"Was Einstein Right? Putting General Relativity To The Test".
Dadface said:Thank you. The main thing I am interested in is whether photons can be detected remotely without the necessity of them ending up at a detector where they get destroyed.
Gravitational deflection. When a photon passes near a compact object, it will be slightly deflected. The change in momentum of the photon will result in a change in momentum of the object, serving to detect the passage of the photon without destroying it.Dadface said:The main thing I am interested in is whether photons can be detected remotely without the necessity of them ending up at a detector where they get destroyed.
UltrafastPED said:This seems most unlikely. If you have references, please provide them!
Bill_K said:Gravitational deflection. When a photon passes near a compact object, it will be slightly deflected. The change in momentum of the photon will result in a change in momentum of the object, serving to detect the passage of the photon without destroying it.
pervect said:If you look at Steve Carlip's "Kinetic Energy and the Equivalence Principle", http://arxiv.org/abs/gr-qc/9909014 , you'll see some references that discuss measurements that concern the effects of static electric and magnetic fields on gravity. For instance, Eotovos experiments on different elements have different amounts of electrostatic energy.
From this, it's not much of a leap to conclude that non-static fields also have an effect. But it may not be direct as you desire.
Dadface said:"single photon detected but not destroyed".
UltrafastPED said:One of several techniques for taking what is called "a weak measurement" - it provides limited quantum information about the object being "somewhat" observed.
See http://en.wikipedia.org/wiki/Weak_measurement
It helps if you have a good grasp of quantum mechanics.
EM radiation is a source of gravity. And it can be detected in principle. But if we're talking about a single photon, that's a whole different kettle of fish. I don't think physics currently has much to say about what effect a single photon has on spacetime curvature. I mean, that would pretty much be a quantum theory of gravity, right?Dadface said:Thank you. The main thing I am interested in is whether photons can be detected remotely without the necessity of them ending up at a detector where they get destroyed. I have found some information on this but need to read up on it.
As you said gravitational effects are very weak but I wonder if these effects can be detected in principle, if not in practise.
PAllen said:I will try to find the reference, but a GR theory paper I recall, that analyzed the mutual attraction of oppositely directed light beams (parallel light beams, somewhat surprisingly, do not - even in theory - deflect each other per GR), calculated a figure for two high powered laser beams. My recollection is that this showed how 'in principle' an effect we're talking about e.g. 10**-29 Newtons for two high power beams.
UltrafastPED said:Here is a 1931 paper by Tolman, Ehrenfest, and Podolsky:
http://journals.aps.org/pr/abstract/10.1103/PhysRev.37.602
And something more modern (1998): http://arxiv.org/pdf/gr-qc/9811052v1.pdf
I only read the abstracts.
PAllen said:Thanks! Your arxiv reference is the one I remember reading. However, my memory of the figure is wrong. The 10**-29 acceleration is due to gravitational waves from the Virgo cluster, while for two laser beams 10 cm apart, the acceleration is only 10**-110 !. Thus GW from virgo cluster have 10**81 time larger effect than a laser 10 cm away. That's really "in principle".
PAllen said:If my calculation is correct, for a laser beam to have a comparable gravitational influence on nearby objects as a 1 gram weight, it would need a power of 10^24 watts.
UltrafastPED said:My thesis advisor is working on such a system, though I don't think they plan to test it that way!
More along the lines of "breaking the vacuum", looking for new physics, and a host of applications:
http://www.technology.org/2013/08/1...elop-new-generation-of-petawatt-scale-lasers/
http://www.eli-beams.eu/
http://en.wikipedia.org/wiki/Gérard_MourouThough I think he is about due to retire ... we're celebrating his 70th birthday later this year at the University of Michigan.
Light and gravity have a complex relationship. According to Einstein's theory of general relativity, light is affected by gravity because it travels through curved spacetime. This means that light can be bent or redirected by massive objects, such as stars or black holes, which have a strong gravitational pull.
Yes, light is affected by gravity on Earth, although the effects are very small. The Earth's gravitational pull is not strong enough to noticeably bend light, but it does cause the light to travel in a curved path around the Earth.
The detection of light and gravity effects is extremely useful for scientists as it allows them to study the behavior of light and gravity in different environments. This can provide valuable information about the structure of the universe and help us understand the laws of physics.
There are several types of equipment used to detect light and gravity effects, including telescopes, interferometers, and gravitational wave detectors. Each of these devices has different capabilities and is used for different purposes.
Scientists use the detection of light and gravity effects to learn about the universe by studying the patterns and behaviors of light and gravity in different situations. This allows them to make predictions and test theories about the structure and evolution of the universe.