A question about gravity and photons

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posted on Oct, 30 2012 @ 04:03 PM
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Do photons have mass?

Obviously they do because they are affected by gravity.

So if you put a flahlight on a set of scales, would it lose weight if kept on?

Or does the light and lack of weight loss (from the flashlight) prove a "quantum effect" in the generation of the photon?


Just a light (pun) question before bed.





posted on Oct, 30 2012 @ 04:14 PM
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reply to post by beezzer
 


Photons do not have mass, but they do have electromagnetic energy that interacts with matter. Einstein won a Nobel prize for discovering the photoelectric effect. It has many practical applications like solar panels, photocells, and lasers.



posted on Oct, 30 2012 @ 04:17 PM
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Originally posted by earthalien50
reply to post by beezzer
 


Photons do not have mass, but they do have electromagnetic energy that interacts with matter. Einstein won a Nobel prize for discovering the photoelectric effect. It has many practical applications like solar panels, photocells, and lasers.


Okay, but Newton's 3rd Law says something about energy neither being created or destroyed.

If energy (in the form of light) is at one end, then there'd have to be a minus on the other end, correct?

Also, don't photons have a theoretical "resting mass"?

Thanks for your reply.



posted on Oct, 30 2012 @ 04:18 PM
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Good question.

Uno .....A photon has no/zero mass.

Duo .... The act of discharging the battery will change the state of the electrolyte inside itself and may influence density/mass......In short, if the scales are sensitive enough, yes you would see a change in the mass of the torch.....but the difference would be so small as to be insignificant.



posted on Oct, 30 2012 @ 04:20 PM
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photons do indeed have mass though i don't know what the numbers are. though it is common to hear that photons are mass-less the energy they carry counts as mass, add to this that light itself can cause gravity and technically bend space time. but before i get ahead of myself and leave the bounds of the original question. the direction the flashlight was pointing makes a difference. the force of the light photons would cause and increase in what the scale would see as weight, if the flashlight were pointed onto it, but, the amount would be so miniscule that measuring it would be a bit tricky (if not entirely ridiculous) at one point someone did the math to find out what extra "weight" the photons from the sun were doing to the exposed side of earth, and it was fantastically small though i cannot find a linky at the moment i would assume a quick round with Google would reveal those figures.

sorry for any spelling, grammar, space placement etc. my keyboard has been danced upon by my 2 year old and doesn't quite type properly anymore.



posted on Oct, 30 2012 @ 04:22 PM
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If they had mass your car would rocket backwards when you switched on the lights


Has anyone seen those little rotating thingys inside what looks like a lightbulb? They have 4 little...reflecters?...that spin around when they are hit by light. One side of each reflecter is white and the other side is black. I always assumed it was light that caused them to spin but the fluffy ones question now causes me to doubt that, so what dDOES make them spin?



posted on Oct, 30 2012 @ 04:23 PM
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reply to post by theinsolentfish
 


If the flashlight was lit onto a medium that collected "light" (photons) would it gain weight?



posted on Oct, 30 2012 @ 04:25 PM
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reply to post by VoidHawk
 


light does indeed have a physical pushing force but its tiny as the mass is the energy and the energy of individual photons is miniscule, go research solar sails, they work on the force exerted from light sources in space, not just the suns light but even light from distant stars can move them, albeit very slowly.



posted on Oct, 30 2012 @ 04:25 PM
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As far as i understand it photons do not have mass and do not get affected by gravity.

So why do photons get sucked into a black hole?

Well the gravity bends space so there is no other direction for the photon to go other than the direction that the black hole has bent space in. As far as the photon is concerned its still traveling in a straight line but in reality its following the gravity induced curve of space.

edit on 30-10-2012 by PhoenixOD because: (no reason given)



posted on Oct, 30 2012 @ 04:28 PM
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reply to post by beezzer
 


that would depend on how accurate the scales were if we used those glowing stars children have on their walls, technically they would gain weight or mass upon charging, but this would be once again, impractical to actually measure. also there would be "extra" weight as the light coming off the glowing star would be pushing in all directions the only reason that they wouldn't cancel each other out is inevitably microscopic flaws in the material would render one side slightly more opaque then the other and it would weigh more or less by a tiny proportion to its actual mass.



posted on Oct, 30 2012 @ 04:29 PM
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Originally posted by PhoenixOD
As far as i understand it photons do not have mass and do not get affected by gravity.

So why do photons get sucked into a black hole?

Well the gravity bends space so there is no other direction for the photon to go other than the direction that the black hole has bent space in. As far as the photon is concerned its still traveling in a straight line but in reality its following the gravity induced curve of space.

edit on 30-10-2012 by PhoenixOD because: (no reason given)


But photons have a resting mass. Does a change in state, register as a change in mass?



posted on Oct, 30 2012 @ 04:34 PM
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Originally posted by beezzer

Originally posted by PhoenixOD
As far as i understand it photons do not have mass and do not get affected by gravity.

So why do photons get sucked into a black hole?

Well the gravity bends space so there is no other direction for the photon to go other than the direction that the black hole has bent space in. As far as the photon is concerned its still traveling in a straight line but in reality its following the gravity induced curve of space.

edit on 30-10-2012 by PhoenixOD because: (no reason given)


But photons have a resting mass. Does a change in state, register as a change in mass?


I didnt know they could even be still, so you have me on that question.

Where do you see that they have a resting mass?

i just found this www.physicsforums.com...

edit on 30-10-2012 by PhoenixOD because: (no reason given)



posted on Oct, 30 2012 @ 04:40 PM
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Do photons have mass?


They have relativistic mass. Photons have 0 rest mass, but, since photons are never at rest, they gain apparent mass from their kinetic energy because of mass-energy equivalence.
Technically, what photons have is momentum, which (and I feel like I'm repeating myself when I say this) is the principle behind things like solar sails.



Obviously they do because they are affected by gravity.


Photons follow the curvature of spacetime caused by gravity. In General Relativity, gravity is described by a stress-energy tensor field, meaning spacetime is curved by energy. Therefore, even photons, being energy, exert their own gravitational force.
Also, if gravitons exist, then they too have their own gravity, which is comprised of gravitons that also have their own gravity...which is comprised of gravitons that also have their own gravity...which...well...you get the picture.



So if you put a flahlight on a set of scales, would it lose weight if kept on?


It would lose a negligible amount of mass by the time the batteries die.



posted on Oct, 30 2012 @ 04:41 PM
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reply to post by PhoenixOD
 


Thanks for the link!



posted on Oct, 30 2012 @ 04:43 PM
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reply to post by CLPrime
 


If photons have momentum, does that mean they accelerate?

PS, thanks for the answer.



posted on Oct, 30 2012 @ 04:48 PM
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reply to post by beezzer
 


No...photon momentum depends only on frequency/wavelength. The velocity side always stays the same (a constant 299,792,458 m/s).

Momentum: p = mv
Photon energy: E = hf
Mass-energy equivalence: E = mc^2, m = E/c^2
Photon velocity: v = c
Photon momentum: p = E/c = hf/c



posted on Oct, 30 2012 @ 05:26 PM
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Originally posted by beezzer
reply to post by theinsolentfish
 


If the flashlight was lit onto a medium that collected "light" (photons) would it gain weight?


Because Photons existence is dependent upon them going at the speed of light, anything that collected them would have to keep them moving. If they stopped, they'd have zero rest mass and would probably cease to exist, giving up their momentum as energy.

Therefore the collector would not gain mass from the Photons, which are essentially mass-less in the first place.

Also, mass causes space-time to distort but you don't necessarily have to have mass to follow the curves of that distorted space-time.



posted on Oct, 30 2012 @ 05:34 PM
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reply to post by chr0naut
 


It depends what's meant by "collects." Any material "collects" photons to some extent when electrons in the material absorb them. When this happens, the material does gain mass. That's the exact opposite of what happens when a flashlight converts electricity to photons that are then released, causing a reduction in the mass of the flashlight.



posted on Oct, 30 2012 @ 10:43 PM
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Originally posted by CLPrime

They have relativistic mass. Photons have 0 rest mass, but, since photons are never at rest, they gain apparent mass from their kinetic energy because of mass-energy equivalence.


This is totally incorrect, and "relativistic mass" is not a concept used by physics.

There is only one mass, it is invariant (doesn't change) and is the quantity that shows up in the correct version of the "mass-energy" equivalence relationship, conservation of 4-momentum (en.wikipedia.org...) p^2 = -m^2, where p^2 is the dot product of the 4-momentum with itself.

In other words, E^2 = m^2 c^4 + p^2 c^2. Photons have no mass, and thus E = pc. You can't just randomly throw away the second half of the equation because you don't like it.



posted on Oct, 30 2012 @ 11:02 PM
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reply to post by Moduli
 


Your last 2 paragraphs are correct (though annoyingly Sheldon Cooper-ish). I would probably have brought up the second half of the mass-energy equivalence equation myself later in the discussion, had we continued on about photon momentum. It has little to do with beezzer's actual question.
Your first paragraph is just your usual successful attempt at being an ass. I am not incorrect. "Relativistic mass" is most certainly a term used in physics...where do you think I learned it?





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