# The Naked Scientists Forum

### Author Topic: speed of charge  (Read 9717 times)

#### thebrain13

• Sr. Member
• Posts: 442
##### Re: speed of charge
« Reply #25 on: 27/08/2006 21:39:36 »
Light does move slower in the presence of mass, relative to an object with less mass in the immediate area. space can be condensed, one inch near a black hole could be ten miles in empty space, so the speed of light would become altered to match the new dimensions of length and time, thus traveling slower.

And gravity can technically accelerate light since changing direction qualifies as acceleration, but it cant alter its speed, since the speed of light is constant. I wasnt implying that gravity will slow down light literally, I was implying that where there is gravity, there is thicker space, hence the slow down.
« Last Edit: 27/08/2006 21:46:56 by thebrain13 »

#### ukmicky

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• Neilep Level Member
• Posts: 3011
##### Re: speed of charge
« Reply #26 on: 27/08/2006 21:46:26 »
quote:
Originally posted by syhprum

Photons have mass because of the energy they carry (it is quite simple to calculate the mass of a cubic meter of sunlight close to he earth {4.8/10^26 Kg}) hence they must be affected by gravity.

syhprum

No!. A photon is massless and is therefore not affected by gravity
quote:
Sometimes people like to say that the photon does have mass because a photon has energy E = hf where h is Planck's constant and f is the frequency of the photon.  Energy, they say, is equivalent to mass according to Einstein's famous formula E = mc2.  They also say that a photon has momentum and momentum is related to mass p = mv.  What they are talking about is "relativistic mass", an outdated concept which is best avoided [ See Relativity FAQ article Does mass change with velocity? ] Relativistic mass is a measure of the energy E of a particle which changes with velocity.  By convention relativistic mass is not usually called the mass of a particle in contemporary physics so it is wrong to say the photon has mass in this way.  But you can say that the photon has relativistic mass if you really want to.  In modern terminology the mass of an object is its invariant mass which is zero for a photon.

http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html

Michael
« Last Edit: 27/08/2006 21:49:17 by ukmicky »

#### lightarrow

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##### Re: speed of charge
« Reply #27 on: 27/08/2006 22:20:53 »
quote:
Originally posted by thebrain13

Light does move slower in the presence of mass, relative to an object with less mass in the immediate area. space can be condensed, one inch near a black hole could be ten miles in empty space, so the speed of light would become altered to match the new dimensions of length and time, thus traveling slower.

And gravity can technically accelerate light since changing direction qualifies as acceleration, but it cant alter its speed, since the speed of light is constant. I wasnt implying that gravity will slow down light literally, I was implying that where there is gravity, there is thicker space, hence the slow down.

The space is not ticker there, is bent. Imagine a semispherical hole in the ground: you cannot measure the diameter of the hole in a straight line, if you are forced to stay attached to the ground; do you know what I mean? This is exactly what happens in a gravitational field; you are forced to move according to the local geometry of space time.
I agree with ukmicky.

#### another_someone

• Guest
##### Re: speed of charge
« Reply #28 on: 28/08/2006 01:41:34 »
quote:
Originally posted by ukmicky
Gravity has no effect on the photon , all gravity does is bend the pathway which the photon has to follow. there's a difference.

Sorry, I don't see the difference – at least insofar as that gravity does to a photon just as it does to an electron, or anything else.

Ofcourse, the means by which any particle is effected is by a change in the pathway the particle follows – but all I was saying is that in that respect, it makes no difference between whether it is the pathway of a photon that is altered or the pathway of an electron is altered.

quote:

Also if gravity could slow down light  (which it cant) then the opposite must surly be also true, with gravity accelarating light faster than c.

http://en.wikipedia.org/wiki/Gravitational_time_dilation
quote:

• According to General Relativity, gravitational time dilation is copresent with the existence of an accelerated reference frame.

• The speed of light in a locale is always equal to c according to the observer who is there. The stationary observer's perspective corresponds to the local proper time. Every infinitesimal region of space time may have its own proper time that corresponds to the gravitational time dilation there, where electromagnetic radiation and matter may be equally affected, since they are made of the same essence (as shown in many tests involving the famous equation E = mc2). Such regions are significant whether or not they are occupied by an observer. A time delay is measured for signals that bend near the sun, headed towards Venus, and bounce back to earth along more or less a similar path. There is no violation of the speed of light in this sense, as long as an observer is forced to observe only the photons which intercept the observing faculties and not the ones that go passing by in the depths of more (or even less) gravitational time dilation.

If a distant observer is able to track the light in a remote, distant locale which intercepts a time dilated observer nearer to a more massive body, (putting aside the fact that a photon cannot be observed without interception with the observer) he sees that both the distant light and that distant time dilated observer have a slower proper time clock than other light which is coming nearby him, which intercept him, at c, like all other light he really can observe. When the other, distant light intercepts the distant observer, it will come at c from the distant observer's perspective.

George

#### lightarrow

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##### Re: speed of charge
« Reply #29 on: 07/09/2006 13:24:43 »
I think that, actually, light is not even bent, near a massive object, if we look at the correct geometry of space-time. We see a bending of light only if we image an euclidean space, but it's not so. What do you think?

#### The Naked Scientists Forum

##### Re: speed of charge
« Reply #29 on: 07/09/2006 13:24:43 »