In the case of black holes, lights are pulled into by great gravitational force exerted by the dying stars (which forms into a black hole). If light has no mass, how is light affected by gravity?
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Photons are not “massless”, they simply have no ‘rest mass’. Mass is simply energy at rest – energy traveling towards the future slower than other energies – and the photon, being as fast as possible, is therefore said to contain no ‘rest mass’. The photon never stops and never loses momentum – all of its energy is in its momentum and it has no rest mass.
Because of this fact, the photon is affected by the curvature of spacetime, thus it’s affected by gravity.
This is also why it is said that mass CANNOT travel at, or faster, than the speed of light. Mass would simply have to no longer be mass to travel that fast, as mass is an equivalent measure of how *not-*fast energy is moving.
You can’t see this too well in the equation E=mc^2 because contrary to popular belief, that equation has been simplified and is much bigger than that.
E=√((m^2 • c^4 ) + (p^2 • c^2 )) is the full equation. This states that the relativistic energy, E, of a moving object is a function of its mass, m, and its momentum, p (as well as the speed of light, c). If you set p=0 and simplify, you’ll get back to the usual E=mc^2. The above equation doesn’t roll off the tongue quite as easily as E=mc^2 but with the momentum term included, it tells a fuller story about how relativity works.
Light always follows a straight path… but if space/time itself is bent, i.e a gravitational field, than light follows that curvature.
Big mass changes the shape of space. We call that change “gravity.” Two masses will “fall into each other” because they changed the shape of space. Since space changed shape, light will follow space and will “bend” along that shape.
Light (photons) have no *rest mass*, but they do have energy. They are affected by gravity as if they had mass equivalent to their energy (because they *do*), according to the famous E=mc^(2).
Time runs slower closer to masses. A wave-like thing traveling through this time gradient will have its path bend. All things are actually wave-like, so all things are affected.
The easy answer is that light is not without mass. It has mass but such an infinitesimally small amount that it can be considered for nearly everything to be neglible. However, a black hole has such stupidly absolutely insanely strong gravity that light has enough mass for it to be considered.
My understanding of the black hole part of the question is that the amount of mass in the black hole actually appears to slow down time so much that the light never reaches the observer. Time stands still from our view so much so that even at the speed of light, the light itself will never reach the outside of the black hole.
So it’s actually the time part of the spacetime distortion of gravity that makes a black hole black.
Light has no REST mass. It has mass. The theory of relativity says everything’s mass increases exponentially as it approaches the speed of light; a light photon with 0 rest mass, which travels at the speed of light, therefore has a mass of 0 * infinity, which works out to a finite number (the universe’s doing, not mine). And that finite mass is subject to gravity, just like any mass.
Things that effect mass also effect energy.
A more accurate form of mass / acceleration calculations should include energy but it makes a very very small difference.
I can’t find it now but I did see somewhere the formula F = mA re-written to include energy by including part of the E=mc^2 formula.
Because the blackhole doesnt do anything to the light, it does it to the spacetime around it. From the lights point of view its still going in a straight line even thou its in orbit around the blackhole within its event horizon.
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