Could a Black Hole Travel Faster than Light?

Possibly in another dimension...

Well that about sums it up! We will never see it, coming or going.

Then it doesn't matter, and the original poster's question is abstruse.

"...it would leave a 'wake' in the fabric of spacetime, much as a moving boat leaves a wake in water, but one here made of gravitational waves. These cause it to lose kinetic energy, by the way, just like a boat's making waves in water dissipates the boat's energy, causing it to slow down. The faster the boat, the more energy you have to pump into it to maintain speed..."

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Hmmm. Are you sure?

As there is no prefered inertial frame of reference, a mass traveling at high velocity with respect to you will see you traveling at high velocity with respect to it. Where are your gravitational waves? Do they cause you to increase velocity with respect to your old self to more closely match the speed of the passing mass?

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Gravitational waves are produced by masses experiencing acceleration. As such they do not slow speeding masses, nor cause energy to be expended just to maintain speed. They limit the acceleration achievable for a given force.

I should have been clearer: the OP is talking about making "a black hole travel faster than light." In order to do that he would need to accelerate it. It is during this acceleration phase that it would create a 'wake.' You are quite correct: a mass moving at constant velocity does not produce gravitational waves, but he not moving it at constant velocity. The wake analogy is inaccurate in other ways as well, though in ways not especially salient to the conversation (GWs being a type of quadrupole radiation, and so forth). The salient point is that, because of the BHs enormous 'rest' mass and the greater gravitational radiation attendant with accelerating one, the OP will have to put more energy into accelerating it due to this effect it than he would were gravitational radiation not an issue.

Since black holes can be of the super-massive variety, how massive do they have to be before it takes all of the energy of the universe to accelerate them?

If it takes that much energy to accelerate them, what speed are the moving at already?

I assume we know since most galaxies seem to have a big old black hole at the center, and we can supposedly measure the relative speeds.

It would be tempting to say that these galactic centers are the unitary reference point for everything else (in the galaxy), and everything else (including space) is moving around them.

Since black holes can be of the super-massive variety, how massive do they have to be before it takes all of the energy of the universe to accelerate them?

Because of the Conservation of Momentum, to accelerate anything requires accelerating mass in the opposite direction. If you accelerate your car to 60 mph, the earth is accelerated in the opposite direction, at a much slower velocity. An equal and opposite momentum, mass x velocity, is gained by both the car and the earth. For each, velocity is inversely proportional to mass.

Kinetic energy is 1/2 mv². (Velocity is measured with respect to the center of mass of the earth plus car.) Because kinetic energy is proportional to the square of velocity, the kinetic energy gained by the car is essentially equal to all of the energy applied. The smaller mass gets the larger share of the energy.

So, to answer the question requires knowing what mass is accelerated in the opposite direction of the black hole. This counter mass would have to be very large for an appreciable amount of the energy to result in accelerating the galactic black hole.

A little known of and understudied force; Van De Merwe force. A force has the power to extract treasures, by any means possible, from those opposing the force. If said power applies speed, (S), relative to chase, (Ch), relative to arresting force, (Af), the resultant runaway force (Rf), will have a negative result of $ + time. This formula fills black holes for many councils and departments.

Fp =S+C_h+A_f -R_f -$ +t.

Note, the result can never be 0 nor equal to 0.

"... what speed are the moving at already?"

If you're moving with them, zero. If you're not moving with them, something else.

"... and we can supposedly measure the relative speeds."

Relative to each other? No biggie. It's done all the time and helpful in identifying whether a collection of galaxies is gravitationally bound or not, ie, part of a galactic cluster or supercluster.

"It would be tempting to say that these galactic centers are the unitary reference point for everything else (in the galaxy), and everything else (including space) is moving around them."

For someone on a merry-go-round, the entire Universe appears to be revolving around them. Same for certain iToy owners I know and Jewish ex-mother-in-laws (I speak from experience).

Cr4 is something of a merry-go-round unto itself, at times. Some of the topics go 'round and 'round, 'round and 'round. Just like the wheels on the bus.

All the live long day.

Rhetorical question, Re: Speed of light....If two objects / particles, approaching the speed of light, as in an Atomic Collider, do, in fact collide, exactly head on, won't the particles broken off of the collision be traveling faster than the speed of light / collision speed? Maybe I am missing something? Obviously, as this must have been thought of previously... Just asking...

No, because the total energy after the collision is the same as the energy before the collision, only now distributed amongst the bits and radiation produced. As the total collision energy is necessarily finite, so must the sum of the energies of the collision products. As it would take an infinite amount of energy to accelerate any bit of mass⁽¹⁾, no matter how small, to the speed of light, then clearly none of them could possibly be travelling that speed⁽²⁾. Very close to it perhaps, but not at the speed of light and certainly not exceeding it.

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(1) a particle having rest mass.

(2) excepting radiation, such as gamma-ray photons, etc. which, having zero rest mass, travel at the speed of light.

Thank you for your explanation. I guess I am stuck with an idea of a cue ball traveling at X speed, colliding with another object ball, and that object reacting at a greater speed...OR a bullet striking an object and the fragments racing off at much high velocities...I'll work on it!

As long as you keep the books balanced - expenditures = income - and don't try to borrow on credit, it all works out.

There was a Professor named Bright

Who travelled much faster than light.

He left one day

In a relative way

And came home the previous night.

- Anon

There was a young fencer named Fisk

whose fencing was exceedingly brisk

So fast was his action,

that Lorentz's contraction

reduced his rapier to a disk.

-----

"You see," said Miss Bright, giv'n to chatter,

"I have learnt something new about matter:

My speed was so great

much increased was my weight,

yet I failed to become any fatter!''

The reality is a black hole spins and if it travelled faster than light it would no longer be a black hole as it would now be visible as light and travelling at the speed of light. So a black hole cannot travel faster than light.

As for leaving a wake such as a boat, a black hole sucks in everything so there would be no wake in front or behind.

It can be assumed that anything entering a black hole would suffer some compression as it nears the entrance and on being ejected, the compression would expand. And in order to expand, (stretch) space time behind it, the hole would need to spin faster than light, ergo, one no longer has a black hole.

One black hole, at the heart of galaxy NGC 1365 is turning at 84% the speed of light. It has reached the cosmic speed limit, and can’t spin any faster without revealing its singularity.

http://www.universetoday.com/109308/how-fast-do-black-holes-spin/

"As for leaving a wake such as a boat, a black hole sucks in everything so there would be no wake in front or behind."

So much for LIGO's findings, ay?

OP here. I expected a spirited discussion since so much of what we think we know about the universe is theory. No one has dissected a black hole. But I'd like to throw out these points:

1) Not all black holes may spin. In fact, there is a name for a non-spinning black hole, "Schwarzchild black hole." Experts argue if such a BH could exist.

2) Spacetime can probably expand FTL. It certainly did during Inflation (another theory), and, if we agree that spacetime is expanding (and accelerating) and Hubble was right, then at some distance objects imbedded in their spacetime will be flying away from us at FTL...and we will never see them.

3) A BH has a singularity where all the mass is concentrated. It is thought to reside at the bottom of the BH 4D "well." (of course, "bottom" doesn't make much sense if the well is infinitely deep). In any case, the singularity is unmoving in it's local frame, not matter how fast the BH might be moving. That is, the BH might be going FTL and the singularity is just along for the ride. This reminds me of NASA's warp drive idea; the ship (or singularity) doesn't violate the speed limit.

4) How does one get a BH to move FTL? I have no idea. As far as I know, we have not observed such, and I'm not at all sure we could. Any considered suggestions would be most welcomed.

1) It's true that it's possible for a black hole to have no spin, but I would think it unlikely. The black hole inherits the angular momentum from the matter from which it's made, and that angular momentum is unlikely to be exactly zero.

https://en.wikipedia.org/wiki/Rotating_black_hole

2) I'm not sure what it means for spacetime to expand faster than light, since light (and everything else) travels through spacetime.

"The metric expansion of space is the increase of the distance between two distant parts of the universe with time. It is an intrinsic expansion whereby the scale of space itself changes."

https://en.wikipedia.org/wiki/Metric_expansion_of_space

3) Spacetime inside the event horizon is completely turned around where space becomes time and time becomes space.

http://www.einstein-online.info/spotlights/changing_places

4) As others have said, anything accelerated close to light speed becomes more massive. At the speed of light, the mass would become infinite. So there is no way to accelerate anything to the velocity of light.

Not only this, some cranial spaces are the most dense form of matter.

I understand the internal cranial pressure to be excruciating in such cases.

You say the matter ingested by the black hole has to impart spin to it, but you have never seen a black hole, maybe you have imagined the event horizon, but the inside guts of the event no, and certainly not the place where all that matter resides in what is essentially a point source.

If you could observe it, how would you determine that it was spinning?

Why is it necessary at all for the black hole itself to be spinning? If you drain water from a sink, you can clearly see the water circling the drain, but the drain itself exhibits no spin (unless you have had too much tequila and the worm).

One last comment, are we sure that energy and that momentum (also angular momentum) are conserved past the event horizon in a black hole? How sure are you of that?

Thanks for the thoughtful input, Rixter. Some of my thinking:

2) From the source you note: "galaxies that are more than the Hubble radius, approximately 4.5 gigaparsecs or 14.7 billion light-years, away from us have a recession speed that is faster than the speed of light." But the distant galaxy isn't moving FTL in it's local frame and neither are we. This seems to imply the space between is expanding FTL.

4) Ah, it is impossible to accelerate anything with mass to FTL. My idea was that the black hole, less it's singularity, is just a hole in spacetime with no mass and can move FTL. And since the singularity is at rest at the infinite "bottom" of the hole, it isn't moving or accelerating in it's frame and we haven't violated the speed limit. Check NASA's idea: http://gizmodo.com/5942634/nasa-starts-development-of-real-life-star-trek-warp-drive for another take on this concept. I'm theorizing a black hole is a real-life example of the space warping that NASA imagines, and therefore it might be possible for a black hole to move FTL.

It cant be.

For once, you are right, whatever it was you were concerned about, it cannot be.