If photons have no mass (maybe this is old science) then why can t light escape a black hole?

answers:
oldprof say: Lacking any external net force on them, photons will travel at light speed in a straight line. When a black hole exists the space surrounding it is extremely warped and compacted inward toward the center of the black orb.
Being mindless quanta of energy, the photons follow the shortest distances across that warped space, which are called geodesics. We can think of these as increments of straight space that around the black hole add up to curved space.
So the photons, massless photons, follow the warped compacted space that leads them into the black hole by crossing its event horizon...the radius where the hole turns black. And that radius occurs at the Schwartzchild radius Rs = 2GM/c^2 where M is the mass of the black hole, G is the universal gravity constant, and c is light speed.
So photons are drawn into black holes because they follow the curvature of space that bends into those dark orbs. And from the general theory of relativity we know that warped space is what causes those effects we attribute to the force of gravity.
What we also know, from physics 101, is that when we fall towards the gravity source, we lose potential energy. It's like falling down a potential energy well where the lowest PE is at the bottom of that well. And for black holes that PE well is very very ... very deep. So...here it comes....
When photons fall into the PE well of a black hole they simply do not have the energy to pop back up and out of that well. They are trapped, which is why that hole is black.

Haji say: Black Holes Have A Full Pull with Gravity

JosephV say: Photons have both corpuscular properties (elastic) and properties of energy (no mass at 'c') in universal space.
However, around the black hole, photons have PLASTIC corpuscular properties. The strange phenomenon of light going in circles around the black hole leads to the formation of a Photon Ring around the black hole. Here in theory, if you shine torch in one direction, the light would come to you from behind you.
Note that the pattern is the same as electrons around the proton in a hydrogen atom in universal space
OR note that the pattern is the same as cosmic 'corpuscles' or the Turbo Gyro Oscillator in cosmic space (this was so before the Big Bang and it will be so as predicted in the Apocalypse to come to be soon enough).
SPECULATION: But, maybe light will escape the black hole in a few centuries from now. Just as a skater gains speed by drawing in the extended arms, the black hole gains speed to reach 'c' at its surface as it gets more compact.  Apocalypse  If light does escape the black hole in concert, then theorists do predict a moment where antimatter would dominate our universe, which would be dissolved in the energy burst??

Tom S say: Gravity is a distortion of spacetime, photons have to travel in spacetime, the "gravity well" created by a black hole it too "deep" for the (massless) photons to escape.

BigBird say: The explanation may be debatable, but an experiment shows that a photon does lose energy and frequency as it goes up in a gravitational field (see Mossbauer Effect). An observer well out in space would say that atoms on the Earth are vibrating more slowly than similar atoms on his spaceship.
i.e. Time runs slower deep in a gravitational field. To function accurately, the GPS system must take this effect into account. A gamma ray emitted by an atom approaching the event horizon of a black hole might be detected as a radio wave by a distant observer (many years later). (Time and the photon are moving very slowly near the horizon.) At or inside the horizon, nothing happens or escapes because time has stopped (from our point of view).
Consider a plane electromagnetic wave passing near a star: The part of the wave front which is closer to the star will be moving slightly slower. The direction of the beam will gradually change.
It would appear that the effects of gravity on light can all be attributed to gravitational time dilation acting on the wave properties of the photons; no photon mass required.

goring say: They may be trapped in a circular path inside the space time content of the black hole. On the other hand is there a positive proof that space time can form a black hole

say: Light does escape a black hole as it has emissions(burps). This is a good question. You should have asked Stephen Hawkings or the other space dude, The African American who is into the space stuff Neil deGrasse Tyson as he talks to us common people.

Jeffrey K say: Gravity is a curvature of space and photons move thru space.
Another way to look at it  Photons have energy and gravity affects energy too.

Andrew Smith say: When you redefine systems to say that photons have no mass, you also have to redefine everything else.
It takes energy to escape a gravitational field.
If there is no mass then the energy required is something other than mg.
As every description of the universe MUST be compatible with known observations there are a great many things that need a different definition once you change things like "F = ma"
But something had to change because even if you could apply a force to a photon it cannot accelerate so SOMETHING had to change to accommodate this fact.

Zirp say: it has to do with escapevelocity I think

jonniebaby say: Escape velocity

Philomel say: Photons have no Rest Mass. When they move they exhibit Mass.

CarolOklaNola say: That photons have no rest mass is an assumption so the math works correctly. The basic problem is you cannot make a photon stationary long enough to measure its rest mass without destroying the photon because of the Heisenberg uncertainty principle. .
The event horizons of black holes is where the laws of classical Newtonian physics and quantum mechanics as we currently understand them break down. At the event horizon, NOT IN the mathematical negative singularity OF the black hole, time stops, becomes 0 AND infinity, eternity.
This is still unresolved.
Good luck on trying to find the rest mass of a photon. All of your funding from the government for your research will down a black hole, be denied.

Who say: It aint just old science its VERY old science
the mass of a photon has nothing to do with it  it dont escape cos there is no path from the inside of the black hole to the outside
(imagine a star sitting on a rubber sheet  the mass of the star creates a huge dip in the sheet
An object traveling close to the star follows the sides of that dip  ( the path it travels has NOTHING to do with the mass of the object only the size of the dip caused by the STAR'S mass  Just as the mass of the moon has NOTHING to do with the orbit it has around the earth THAT orbit is determined by the mass of the EARTH NOT the moon)
So it travels in a curve  If the path its following leads to space OUTSIDE the dip then it will continue on its way in a different direction than before (cos it followed a curved path for a while)
If its path DONT lead to space then it will fall and hit the star
With a black hole there are NO paths that lead to outside the black hole so NOTHING can escape it
If you aint noticed NOWHERE does the mass of the object inside the "dip" (black hole) make ANY difference to the path it takes  THAT path is ONLY to do with the mass of the object that created the "dip"(in this case a black hole)

Fabio _ say: They do have mass. Some more than others.

Dixon say: The curvature of spacetime due to the mass of the black hole and the energy of individual photons.

Kevin7 say: E equals mass times c squared ( c is the speed of light) from Albert Einstein says Energy is a form of mass

Guru Hank say: No rest mass.

say: Even though I failed university physics I distinctly remember the lecturer saying once that photons have a mass of less than 10^66 kgs.
