if something like a black hole can travel can it travel past the speed of light. I know that the faster that something goes the more it weighs and the slower it will eventually go but does it affect a singularity the same… ie would there be a drag on a single point because physics (as far as I know) breaks down in a black hole. Could it travel past the speed of light
Black holes can’t travel faster than light, the theory which predicts also prohibts this behaviour in objects. Yes the black hole would appear to gain mass to an observer. The laws of physics may well breakdown at the singulaity but the black hole from the p[ov of the rest of the universe is still governed by the same laws as the event horizion shields the singlarity.
This brings up an interesting question, though: if a black hole is travelling at a high speed, does that mean that the event horizon would lag behind the singularity? I.e., would the singularity move to a more forward position within the event horizon, instead of the exact center? Would the event horizon change from a sphere to an oblate spheroid? Would the singularity ever cross the event horizon? I’m guessing this would occur at the speed of light, to preserve the Cosmic Censorship Principle.
I think you can get oblate spheroid event horizons around rapidly spinning black holes… but a relativistic black hole would seem spherical to a co-travelling observer.
Minor nitpick: as an object moves faster, it has more mass (not weight) and it doesn’t slow down but requires more force to accelerate. The basic equation of motion, Force = mass * acceleration (F=ma), describes the acceleration resulting from applying a force to a given mass. This usually means that a given force will produce the same acceleration regardless of the current velocity, but as you reach significant fractions of the speed of light and the mass-change effects become non-negligible, the mass of your body increases and a given force produces less acceleration. This just means that as you approach the speed of light, it requires more and more force to go a little faster. In no case does it describe an effect that would slow down a moving body.
Drag on an object is force imposed by the environment so it’s dependent on where the object is traveling. You could easily eliminate drag by choosing your trajectory to exclude any factors which contribute to drag, but the force required for each incremental acceleration would still increase due to the increase in mass.
A singularity can become naked if it spins fast enough.
How? I always though naked singularities were impossible in our universe?
what do you guys mean exactly naked??? no event horizan???
I have no idea about what i’m going to say it’s just a stab in the dark I have no grounds to back this up it’s just an idea I had
How would the event horizon effect the singularty if at the speed of light there could be no event horizon. I say this because if it’s going the speed of light then shouldn’t the light thats in front of the direction the singularity is heading get sucked into the singularity and anything behind the singularity would now be following behind the singularity. Why does increassed mass require more force when in space there isn’t exactly much friction?
Yes, but if the observer is co-travelling, then the black hole is hardly relativistic, is it? The velocity must be relative to some stationary observer, in which case it would seem that the singularity would move from the center of the black hole towards the forward edge of the event horizon in the direction of motion, while the event horizon becomes an oblate spheroid, foreshortening in the direction of motion.
Actually, come to think of it, maybe it would move to the back of the event horizon. As shea241 pointed out, it seems like the black hole would suck up more light in front of it than behind it as it is travelling, kind of like a black hole Doppler shift, leading to the event horizon being forward of being centered on the singularity.
Can anyone resolve this? Relativity always makes my head hurt.
Care to expand upon that? I thought most physicists (including Stephen Hawking, if I’m not mistaken) believe that naked singularities are forbidden. Could it perhaps be that in order for the singularity to become naked, it would have to rotate faster than the speed of light, and so is forbidden?
That’s exactly what we mean. A naked singularity is one that doesn’t have the modesty to hide itself behind an event horizon. The Cosmic Censorship Principle postulates that the universe’s sense of morals always steps in to prevent this indecency from happening – i.e., that any conceivable instance that could expose a singularity is prohibited by some other factor. In other words, a singularity is always in an observer’s absolute future (or absolute past in the case of the Big Bang). I believe that the CCP is pretty well supported, but I could be mistaken.
This is like the intro-to-relativity problem that asks what happens if a car is going the speed of light and turns on its headlights. The answer (I believe) is that they work normally because the speed of light is constant even in a moving reference frame.
Friction and other sources of drag will slow down a moving object, but that’s not what we’re talking about. If you have an object which is moving, you have to apply force to make it move faster (accelerate). How much acceleration you get from a given force is governed by F=ma. If mass increases with velocity, then the more you accelerate, the more force you need to keep accelerating.
Drag, whether frictional or otherwise, is just another force on the body. Drag decelerates a moving body, so as mass increases with velocity, drag will become less important because a relatively constant force will mean a smaller deceleration (assuming your drag force isn’t also dependent on velocity…).
ok the mass would increass and increass but what would that matter I mean it is a singularity why would it matter how heavy it is, it’s not like it could be crushed.
Your OP implied that the increase in mass would slow it down. I was simply pointing out that an increase in mass just makes it harder to accelerate, which is not the same as slowing down. In fact, quite the opposite because the increased mass will make it much harder to slow down since slowing down is just a type of acceleration.
This may have little or nothing to do with your actual question. I was just correcting your expression “the faster that something goes the more it weighs and the slower it will eventually go” because that might indicate a misunderstanding which might make getting to the answer that much harder.
A black hole can’t go the speed of light, any more than anything with mass can.
If a black hole is moving very quickly, then it will not gain mass, unless you use a non-conventional and not particularly useful definition of “mass”.
The event horizon would move exactly as fast as the singularity.
A black hole which spun too fast or got too much charge would be naked, the implication being that it can’t spin that fast or gain that much charge.
Do you mean that black holes are not affected by mass changes caused by relativistic speeds? Are black holes exempt from the usual M = M[sub]0[/sub]/sqrt(1-v[sup]2[/sup]/c[sup]2[/sup]) that affects less exotic matter?
If you want to use F = ma in a relativistic scenario then in the longitudinal direction
Force = gamma cubed time acceleration and in the transverse direction Force = gamma times acceleration. In between these extremes the relationship is some kind of matrix.
Gravitational mass, or rest mass, or just plain mass is unaffected by velocity. Relativistic mass is an outmoded concept and the vast majority of physicists don’t use it. One of the main reasons it isn’t used is because it’s confusing. People tend to think that moving objects get heavier or that gravitational effects increase.
Cite? I’m not arguing the point, just asking to be brought up to date. All my references discuss the relativistic mass formula I cited earlier.
From the physics.faq
http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html
Ring: thank you for the cite. That was very helpful. What I distill from the FAQs linked on that page is that the concept of relativistic mass is not wrong per se but physicists choose not to use it because it cannot be blindly substituted for rest mass and it confuses the issue (particularly for laymen such as myself). However, kinetic energy does change with increases in velocity just as relativistic mass would describe, so my comments above about forces and accelerations are correct. Obviously my use of F=ma in this situation was an oversimplification, but the basic concept is correct.
I apologize if the inaccuracies in my terminology derailed this thread since I intended my contribution to simply correct a semantic problem with the OP.
my basic idea behind all of this was that because a singularity breaks the laws of physics (unless that is a mistake or myth or theory long dead) then it doesn’t really follow the rules of the universe so maybe it could be accelerated to the speed of light as it might not need infinite energy to accelarate infinate mass… is that in any way possibe?