if light could always travel in a vacum would it always travel at the speed of light or would it eventually slow down?
What makes light go?
If we could see past the event horizen would light orbit around the singularity where the propagation of gravity was equal to the speed of light?
I have more but I have to go right now for some Tim’s also I know this is my thread but anybody else that can think of a question then post it.
Light can’t slow down. It can be absorbed and re-emitted so that it appears to slow down, and information pulses encoded in light can slow down, but the speed of light itself is c, period.
Light can’t stop. Classically, light is produced by a moving electric charge, which propagates a changing electric field, which propagates a changing magnetic field, which propagates a changing electric field, which propagates… In quantum physics, light is composed of massless particles, so there’s no reason why they’d NOT go.
Um. I’m not sure what you mean, here. Gravity and light both propagate at c. But yes, I think a singularity curves space so that light traveling in a straight line would also be orbiting the singularity. AAMOF, I think that IS the event horizon.But I confess that this isn’t my area, and Chronos or somebody will be along shortly to spank me.
ok to continue with the questions.
can all or any mass be transformed into light?
Is light pulled by gravity (black hole for example) or does it always follow a straight path that just happens to follow a curve in space.
If you travel at the speed of light doesn’t time stop and if it does then how does light continue to travel?
This perplexes me even more from the last reply from nametag stateing
Light can’t stop. Classically, light is produced by a moving electric charge, which propagates a changing electric field, which propagates a changing magnetic field, which propagates a changing electric field, which propagates…
Does physics really break down in a black hole and if it does could it be possible that physics breaks down after going faster then the speed of light?
Umm thats it for now i’ll think of more later.
Qualitatively yes. The actual physics is much more complicated, but basically you have a place in spacetime where light stays in place. That’s the event horizon.
When you say that light travels in “straight lines”, that’s only true locally. Light travels on what is called “geodesics” which are paths that require no acceleration in the warped spacetime configurations of general relativity.
It is technically not true to say that the light “orbits” the black hole at the event horizon since orbits are really due to the Keplerian limit of gravity. That certainly doesn’t apply in the case of black holes.
Indeed. The sun does, after all, shine, right?
Yes, time stops from the perspective of something travelling at light speed. That doesn’t mean it stops from the perspective of someone watching something else travelling at light speed.
Physics, I think, works just fine inside a black hole. Physics works just fine going faster than the speed of light, were such a thing to have meaning. Our present understanding may not be able to explain either, however.
If current theories are okay, the only thing that’s truly screwy inside a black hole is the singularity. There, we don’t know exactly what to say. But it’s not something we’ll be able to do measurements on anyway, so…
Also if current theories are correct, things going faster than the speed of light is… well, problematic at best.
And what makes the earth turn. And what makes the moon go around. And what makes meteors whiz along.
Wrong questions. Everything ALWAYS moves. Automatically. That’s how the universe always has worked.
The real question is, WHAT MAKES THINGS STOP. The answer is simple: friction.
If you’re living on the surface of the Earth, then you’ll get the wrong idea about reality. After all, down here on earth everything “naturally” comes to a halt. And it SEEMS as if an engine (etc.) is needed to make things move. Nope, wrong. In truth, things come to a halt because of drag. They rub against the ground, or they feel air-friction. In truth, the purpose of engines is to defeat friction. If you were out in space, then you’d see that everything is moving around all the time, no engines needed. In space, special things are needed to bring objects to a halt.
What makes light go? Simple answer: photons are already moving when they are created. Since there is nothing to slow them down, so they keep going.
Second, more complex answer:
photons have no rest mass, therefore they try to travel infinitely fast but they run into the maximum speed barrier. Particles with no rest-mass cannot be slowed down, only absorbed. Things like electron beams will slow down in air because of friction. But light will not. If anything manages to slow down a photon even a tiny bit, the photon speed falls to zero, and the light is absorbed by the object that slowed it.
Kinda makes me wanna say, “We’re all made of star dust”, but that’s not really relevant at all.
Any existing particle, when combined with its antiparticle, will turn into light.
It’s kinda hard to know exactly what goes on inside of a black hole, and most things we know about black holes currently is speculation, albeit well thought out speculation. I wouldn’t say however that “physics breaks down”, we simply don’t really know much about it at the moment. As for things traveling faster than the speed of light…, well, problematic is understating it. Given what we know now, we’re really not sure if objects can travel faster than the speed of light, let alone what happens when they do.
Yes.
Option number 2 is the qualitatively correct one.
Time doesn’t stop. You’ve just transferred to a frame where your space axis and your time axis are one and the same. Traveling happens only with respect to things that are not traveling the speed of light which when the time axis and the space axis are not one and the same. Things that travel at the speed of light look like they are traveling to someone who is looking at them. When you are a reference frame you don’t have any information that you are moving at all, so this is actually a problem of frame-dependence and is really a more general question than you make it out to be. If you transform into a frame that has a constant velocity then you cannot tell the difference between it and any frame that is “at rest”.
Physics never breaks down. We just sometimes don’t know what the rules are. The universe, however, doesn’t care if we don’t know what the rules are and will continue to do what it does anyway.
We have no physical model for the interior of a blackhole near the singularity. To do that right you have to have a theory of quantum gravity which no one has.
Physics does not break down when you go faster than the speed of light. No object with mass is allowed to go equal or above the speed of light. Period. An object with no mass MUST travel the speed of light. Them’s the rules. There is no break-down.
Things that are not physical objects can travel faster than the speed of light. For example, if I shined a laser at the moon and swept it all the way across the moon in a single second (easy to do since the angular size of the moon is pretty small), the “spot” on the moon will move faster than the speed of light. No information, however, is transmitted from one side of the moon to the other by means of that spot so special relativity is not violated.
Shadows can also travel faster than the speed of light. They are not, however, physical objects and also carry no information.
Yes to both. That’s exactly the mechanism by which gravity pulls on anything, light or matter. In the absence of non-gravitational forces, an object will follow a “straight” path through spacetime. Since spacetime is curved, those “straight” paths are also curved, in a way which we describe as an attractive force.
And the distance at which light will orbit a black hole is not the event horizon. It’s outside the horizon; if memory serves me correctly, it’s 1.5 times the radius of the horizon. You can also get orbits that are almost circular this way: A photon can come in from a distance at just the right angle that it’ll loop around the black hole once, or twice, or ten billion times, and then come back out in an essentially random direction.
The last stable orbit around a balck hole is sometimes called the photon sphere and it lies (for a Scwarzchild black hole) at 1.5 x the radius of the event horizon (i.e. outside of the event horizon, in the case of the Scwarzchild black hole), here light will trace a closed loop around the black hole.
Thanks so far guys I just had one last question. Is the conversion of mass to light a possible reason for the uinverse expanding for example a baloon with some water in it that turns to gas?
In the way that I (IANAP) understand it, think of it as light propagating within a spacetime field. A drop of disturbance on this would spread out (as light in your case) as “information” of its disturbance simply by the 2nd law of thermodynamics. If its why the 2nd law works your asking then…nobody knows.
As for the last question, while all mass will (in theory) eventually dissipate into energy if the universe expended infinitely, I dont see how mass converting into energy actually drives this expansion. The analogy of water in ballon sort of fails as the water, in order to expand will require an input of energy from outside the ballon. The universe on the other hand, is assumed to have no “outside”.
The bottom line is still that it IS possible for conversion of mass to light as a possible reason for the universe expanding. Simply because theres just so darn much that we dont know about the universe.
A laymans take~
I kind of thought everything travels at the same, constant “speed”, it’s just that, with light, motion is maximally in the space direction (assuming c is the limit), and with something at rest, “motion” is maximally in the time direction.
Of course, I always mangle the English language when I try to express something about space-time intervals. And the whole concept of “motion” through time is controversial. Be that as it may, I guess it’s fair to say nothing can sit “still”, light or otherwise. We’re always blasting through time or space to some degree.
From this link on Black Holes
" As you get closer and closer to the horizon, the light that you’re emitting takes longer and longer to climb back out to reach Penelope. In fact, the radiation you emit right as you cross the horizon will hover right there at the horizon forever and never reach her. You’ve long since passed through the horizon, but the light signal telling her that won’t reach her for an infinitely long time.
If the light isn’t slowing down due to the pull of gravity, what exactly is happening to it as it tries to escape the gravity of the singularity?
Intense gravity fields, such as those around black holes, distort time as well as space. The light isn’t actually slowing down (because, of course, it’s always going the same speed) but time itself is slowing down, making the light appear to slow down. From the frame of reference of someone near the event horizon, everything seems normal. But from someone far from the event horizon, everything down near the black hole seems to happen in slow motion.
I shouldn’t have said before that this was my last question because here is another one
Can light be turned back into mass. If this is possible does it happen in a black hole.
Nishroch Order said
“The analogy of water in ballon sort of fails as the water, in order to expand will require an input of energy from outside the ballon. The universe on the other hand, is assumed to have no “outside”.”
What if there was an object in the baloon that turned the water into steam like the sun turns matter into light.
I thinkn the fact that a balloon requires some sort of enrgy inout to inflate is a minor flaw in what is only a rough analogy. Remeber though that with the balloon model we’re only intrested in the surface of the ballon and not it’s interior.
Yes, infact as far as I’m aware the radially co-ordinate velocity of light of 0 at the event horizon is only valid for a remote observer, which would correspond to an infinite seperation.
Its ok, go ahead and ask questions. This should be the place to do so.
Yea light can be turned to mass. E=mc^2=E. Physics is such that it allows things to work both ways, but reality as we see it dont always work that way. Whether that happens in the black hole is beyond me.
However, something else interesting does happen at the border of the event horizon. Mass appearently DOES pop out of nowhere at this edge. According to my rusty memory, matter-antimatter pairs pop out all the time everywhere in the universe. They “borrow” energy to exist and quickly annihilate with each other to return this borrowed energy.
However, if such a pair appears at the precise edge of the horizon, and as luck would have it the antimatter counterpart gets sucked into the blackhole, matter would be…in a sense…born. Is this where gravity and EM link?
Haha, ok lets not argue about analogies shall we. 
IF there IS something that turns mass to light. Be it gravity or some decaying of the particle by itself (there probably is i think). It’ll take alot of imagination to propose that this actually drives the universe to expand against gravity. Well, be imaginative enough and you might just be the next Einstein.
The “you” in that statement represents mass and light is energy. If “you” travel at the speed of light, “you” have become energy and time is irrelevant. [sup]Or something like that.[/sup]