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Black holes are currently thought to just be big things (lack of better word) of gravity that pull stuff in. If gravity relies on mass and light has no mass, how is light pulled into black holes?
Light does have mass. You're thinking about rest mass which is different. In The Evolution of Physics - from Early Concepts to Relativity and Quanta, Albert Einstein and Leopold Infeld, Simone & Schuster (1938), page 221 - Einstein commented on an observation made by an observer inside an accelerating elevator that light is ‘weightless’ Einstein wroteOriginally posted by ShawnD
Black holes are currently thought to just be big things (lack of better word) of gravity that pull stuff in. If gravity relies on mass and light has no mass, how is light pulled into black holes?
This same sentiment was expressed by Feynman in Feynman Lectures Vol - I, page 7-11. Section entitled Gravitation and RelativityBut there is, fortunately, a grave fault in the reasoning of the inside observer, which saves our previous conclusion. He said: “A beam of light is weightless and, therefore, it will not be affected by the gravitational field.” This cannot be right! A beam of light carries energy and energy has mass.
One feature of this new law is quite easy to understand is this: In Einstein relativity theory, anything which has energy has mass -- mass in the sense that it is attracted gravitationaly. Even light, which has energy, has a "mass". When a light beam, which has energy in it, comes past the sun there is attraction on it by the sun.
The bending of space is not what causes the bending of light. In fact Einstein's first calculation of the deflection of light by the sun did not take spatial curvature into account and yet there was still a deflection. When spatial curvature is added then there is more delfection. So curvature contributes to deflection but is not the sole cause of delfection. Also - Spacetime curvature is not a neccesary condition of the gravitational attraction of light.Originally posted by Zhou Yu
Basically anything that bends space time will cause light to bend, therefore even a large sun will bend light even though it will not be to the same extent as a black hole.
Originally posted by pmb
Light does have mass.
You're thinking about rest mass which is different.
Show me where I said "ShawnD you are wrong" and I will delete it.Originally posted by Ambitwistor
According to one definition of mass, light has mass. According to another, it doesn't. ShawnD is not wrong.
The so-called "invariant mass" is the name given to the magnitude of the total 4-momentum of a system of particles. The term "rest mass" is the name given to the m0 in"Rest mass" cannot be defined for light, which is never at rest. Light has zero invariant mass. Rest mass is a special case of invariant mass that applies to massive bodies.
where "m" here means "rest mass." I see no mention of the term invariant mass in that text. Its not a widely used term in all of relativity. In other texts it refers to systems of particles only.The above formalism is valid only for particles with nonzero rest mass, m != 0. The corresponding formalism for a particle with zero rest mass can be obtained from the above by taking the limit as m -> 0 and dT -> 0 with the quotient dZ = dT/m held finite.
That link you posted has many conceptual errors in it. I.e.Question: If light can be pulled into a black hole due to huge gravity forces, does this necessarily mean that light has mass?
Answer: This is an exceedingly subtle question. The photon (particle representation of light) is called a massless particle, because it has no rest mass. It's never sitting still. So all its energy is energy of motion. Ordinary objects, like a pencil, have both a rest mass-energy: E = mc2, and an energy of motion (kinetic energy): E = (1/2) mv2. Note the remarkable similarity between these forms.
But the most honest answer to your question is yes--light has mass. I say this, running against the physics grain (photons have no mass), because the photon in all respects behaves as if it has mass. It is affected by gravity (light is deflected by gravity). It carries momentum. It creates dimples in spacetime (albeit tiny), like any mass or energy does. The fact that it has no rest mass is irrelevant in many respects, because it never travels any slower than light speed!
Theoretically this has never been the case. That's more of a poor-man's view of the physics. In all truly rigorous definitions and derivations the term relativistic mass refers to the ratio of momentum to speed. A.P. French was right on the mark in his text on this point. However he refers to this ratio as inertial mass, not relativistic mass. To be precise, relativistic mass, m, is defined such that mv is a conserved quantity. So anything which has momentum has mass. For a rigorous definition and for the derivations seeSometimes 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.
These are two different topics which are related. The other thread has to do with whether a particle's mass increases with speed. This thread has to do with whether light has mass and as such is the reason why it is deflected by gravity. This, however, is often taken to be the same question. However it was not so to Einstein. In fact Einstein would not have used relativistic mass in the first case but would use relativistic mass in the present case.Originally posted by Integral
Isn't there already a thread with this same argument? Please restrict this argument to that thread!
Integral
If you got the impression that I think my way is the only way then you got the wrong impression. I've never made that claim nor have I ever had that thought it, especially since I believe that definitions are beyond question. There is calculation, historical fact and modern usage (e.g. texts, journals etc). That is what I've discussed.pmb, stop arguing about definitions, and stop acting like your way is the only way -- you know it isn't.
- Warren
Pete,Originally posted by pmb
If you got the impression that I think my way is the only way then you got the wrong impression. I've never made that claim nor have I ever had that thought it
Light does have mass. You're thinking about rest mass which is different.
I'll do better than thatPlease stop arguing definitions unless the meaning is clearly relevant to the discussion (in this case, the arugment just isn't relevant).
Wait... are you sure this is right? If I remember correctly, and there is a good chance that I'm not, GR puts gravitational attraction in terms of distorted spacetime. You can't have any gravitational attractive, massive or not, without such spacetime distortion, or implicitly taking into account of spatial curvature.The bending of space is not what causes the bending of light. In fact Einstein's first calculation of the deflection of light by the sun did not take spatial curvature into account and yet there was still a deflection. When spatial curvature is added then there is more delfection. So curvature contributes to deflection but is not the sole cause of delfection. Also - Spacetime curvature is not a neccesary condition of the gravitational attraction of light.
Yes. That orbital distance is 1.5 times the black hole's Schwarzschild radius.Originally posted by †ony
So is it possible for light to orbit a black hole if it goes by at just the right distance and speed relative to the black hole?
According to Einstein's theory of general relativity, the massive gravitational force of a black hole curves the fabric of space-time, causing light to follow a curved path and appear to bend.
Once light crosses the event horizon of a black hole, it cannot escape due to the intense gravitational pull. However, light can still be bent and deflected by the black hole before reaching the event horizon.
No, we cannot see the back of a black hole because light that passes the event horizon cannot escape and therefore cannot reach our eyes. However, we can observe the effects of light bending around a black hole, such as gravitational lensing.
The larger the mass of a black hole, the stronger its gravitational pull and the more light it can bend. Therefore, larger black holes are more likely to cause noticeable bending of light compared to smaller black holes.
No, in addition to light, other forms of energy and matter can also be affected by the gravitational pull of a black hole, causing them to follow curved paths and be deflected.