Blackholes and EM waves

[abskebabs]

Hi everybody. The thought just recently hit me and I'm sure there is probably a good explanation for this phenomena, but why; when photons are massless particles, do they get sucked into black holes with their strong gravitational field? Is there something fundamaental here which I have not considered?

[insane_alien]

yeah photons are affected by gravity. its due to curved spacetime and the shortest possible path being a curve.

[BhavinB]

^^ Just to add to your answer is mentioning Fermat's Principle which basically says the path light takes from A to B is the shortest possible one.

[5614]

And around a blackhole the shortest route always leads straight into a blackhole... that is what a blackhole does, warp space-time so much that it will bend in on itself (ie. into the blackhole).

[Norman Albers]

Light we can understand as E and M fields pushing each other along. THE NEWS IS THAT GRAVITY AFFECTS THIS FIELD PHENOMENON AS IT DOES WHAT WE CALL MASS. Where our vision is short is in using the word mass in the first place!

[Klaynos]

Light we can understand as E and M fields pushing each other along. THE NEWS IS THAT GRAVITY AFFECTS THIS FIELD PHENOMENON AS IT DOES WHAT WE CALL MASS.

 

This is news?

 

Where our vision is short is in using the word mass in the first place!

 

Why?

[CanadaAotS]

can't photons bend spacetime too? They have a relative mass which has to do with their energy

[Norman Albers]

Was this not the original question? Also, yes, energy over c-squared is equally a source of gravitation. I see mass as just "canned light". Eat supper and enjoy molecularly "canned light". What else is there?

[Klaynos]

Was this not the original question? Also, yes, energy over c-squared is equally a source of gravitation.

 

For the CORRECT! form of E=mc² see my signiture...

 

OK imagine space is like a rubber sheet, you place a ball on your sheet, this ball represents a mass, it bends the sheet downwards. Light travels in streight lines in space, it's just now the streight lines are being curved by the mass curving space. This is why gravity effects photons.

[timo]

Hi everybody. The thought just recently hit me and I'm sure there is probably a good explanation for this phenomena, but why; when photons are massless particles, do they get sucked into black holes with their strong gravitational field? Is there something fundamaental here which I have not considered?

Yes, there´s something fundamental you haven´t considered: If you have any gravitational field G (<- Newtonian Gravity) or equivalently any spacetime g (<- General Relativity), all particles with a given starting position and a given starting velocity will have the same movement in this field. In other words: The mass of a particle does not (directly) influence it´s movement in a gravitational field.

 

In Newtonian Gravitiy this is because a = F/m, F = G*m => a = G. The mass doesn´t enter the movement equation (a=G). You do have problems with massless particles here but you can´t consistently describe massless particles in Newtonian Physics, anyways.

 

In Relativity, you don´t have forces. Instead you make an assumption which usually is refered to as "particles take the shortest path through spacetime". This also leads to a movement equation which is independent of the particle´s mass.

[□h=-16πT]

And around a blackhole the shortest route always leads straight into a blackhole... that is what a blackhole does, warp space-time so much that it will bend in on itself (ie. into the blackhole).

 

No it doesn't. You can get stable orbits about black holes.

[abskebabs]

In Relativity, you don´t have forces. Instead you make an assumption which usually is refered to as "particles take the shortest path through spacetime". This also leads to a movement equation which is independent of the particle´s mass.

 

Cool. I'd love to learn more about this, and I'm kind of torn I didn't pick physics as my course to do at University. I'm not interested in a career being a physicist, but I'd love to learn much more about this in detail...

[Norman Albers]

I see us as mathematicians and storytellers. We can, up to a point, move the audience with the idea that "masses produce forces at a distance". We experience this and so any story which expresses what we experience draws our applause. Then the next storyteller speaks of "rubber membranes" which draw things along their characteristic curves. We know damned well there is not rubber here, but this is a very good story that tells us something of how space and its contents are connected. Affine connections deal with the smooth connection of vector fields in differentially small neighboring locales. This gives us a better handle on just how that force gets out to that distance. We applaud, and realize how subtle it is to know anything at all! I use some beautiful old textbooks, one written in 1928. I say that becuase the writers are entirely lucid in presenting their structures and their limitations. By being clear on all assumptions they give me the opportunity to take off with new ones! How nice to read, "If the reader is confused by the assumptions behind Planck's black-body spectrum, this confusion is no greater than that which existed in the minds of the participants in 1911."

[timo]

Cool. I'd love to learn more about this, and I'm kind of torn I didn't pick physics as my course to do at University. I'm not interested in a career being a physicist, but I'd love to learn much more about this in detail...

Not completely sure what you mean with "this". General Relativity in general or how the movement equation is derived in it? Keywords you could look for to read up on the movement equation are "geodesic equation", "christoffel symbols" and "connectivity". I have a the derivation online on WiSci (http://www.wisci.org/wiki/Geodesic_equation) but I´m not sure if it´s understandable without knowing some basics about relativity.

[Norman Albers]

By "this" I mean the depiction of mass/energy densities affecting the geometry of spacetime by a smoothly describable change under differential transplantation. Do I recall correctly the sense of affine connections? Adler, BAzin, Schiffer, p44: speaking of "a general law for transplantation of a vector psi^i at the point 'x' into the quantities ..............psi^i + d(psi^i) at the point x + dx. It is a law of affine character; that is, it has invariant structure under a linear transformation of the coordinates."

[CanadaAotS]

Was this not the original question? Also, yes, energy over c-squared is equally a source of gravitation. I see mass as just "canned light". Eat supper and enjoy molecularly "canned light". What else is there?

 

So that turkey dinner of yours has the energy to blowup the world lol

[CanadaAotS]

No it doesn't. You can get stable orbits about black holes.

 

yah, even light can orbit it. All blackholes have a light band just outside the point of no return.

 

we're orbiting the massive blackhole in the center of our galaxy as we speak.

[Norman Albers]

Given normal and thorough mastication of your turkey you will remain in the realm of a few electron volts, because that's about the energy of chemical bonds, I think. I'm not sure about carbon, but as noted, 13.6 volts is high in these realms. This actually gives me pause for thought: why is it that so many things are just so: visible sunlight energies, common chemistry energies, batteries, and us........................................earth, air, fire, water....................................If you posses thermonuclear teeth, on the other hand, or if you place the turkey in the THERMONUCLEAR BOX, you can really do some cooking!!! Quite a few magnitudes more.