# If you travel faster than the speed of light, do you open up a black hole?

#### Gamish

If you travel faster than the speed of light, then your mass would become more than infinite (imposable), so, you would generate a gravitational field so large, that according to GR, you would open up a black hole. Is this true? My point here is not to prove that on can travel faster than c, as the numbers just don't add up.

Sometims, time runs too fast, time to :zzz:

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#### Chronos

Gold Member
Nope. FTL travel is prohibited under GR. Hence, the question is irrelevant and unsolvable using GR field equations.

#### pervect

Staff Emeritus
Gamish said:
If you travel faster than the speed of light, then your mass would become more than infinite (imposable), so, you would generate a gravitational field so large, that according to GR, you would open up a black hole. Is this true? My point here is not to prove that on can travel faster than c, as the numbers just don't add up.

Sometims, time runs too fast, time to :zzz:
Nope, take a look at the sci.physics.faq on tachyons sometime. The mass of a tachyon would be imaginary (if they existed), not infinite.

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html

#### Gamish

um, ?????

OK, then let me ask this. What the heck is the purpose of a black hole? According to GR, if an object is so massive that objects are attracted to it by its gravitational force, at faster than c speeds, then the whole object will collapse on itslelf or something, so, does not matter and light travel faster than c in these black holes?

In the beginning, there was something, in which everything came into existence. For if in the beginging, there was nothing, than nothing could have come into existence that existst today, and if something did come from nothing, that that "nothing" was really something in the first place. Now, is this "something" a being, to explain the lack of entropy in the universe? or just matter and or energy? take that Chronos, rofl.

#### misogynisticfeminist

This thread is extremely speculative, but maybe I might try to rephrase this a little.

If I travel near the speed of light and my mass tends towards infinity, is there something analogous to the chandrasekhar limit in which I collapse on myself and form a black hole?

#### Chronos

Gold Member
misogynisticfeminist said:
This thread is extremely speculative, but maybe I might try to rephrase this a little.

If I travel near the speed of light and my mass tends towards infinity, is there something analogous to the chandrasekhar limit in which I collapse on myself and form a black hole?
Nope. In your reference frame your mass and size does not change no matter what speed you travel. Bear in mind that the Chandrasekhar limit is the same in your reference frame as it is in any other reference frame.

#### Chronos

Gold Member
Gamish said:
OK, then let me ask this. What the heck is the purpose of a black hole? According to GR, if an object is so massive that objects are attracted to it by its gravitational force, at faster than c speeds, then the whole object will collapse on itslelf or something, so, does not matter and light travel faster than c in these black holes?
According to GR, mass possessing objects are limited to v<c velocities.

#### pervect

Staff Emeritus
misogynisticfeminist said:
This thread is extremely speculative, but maybe I might try to rephrase this a little.

If I travel near the speed of light and my mass tends towards infinity, is there something analogous to the chandrasekhar limit in which I collapse on myself and form a black hole?
No. There is an entry in the sci.physics.faq on this if you want more info, but the quick summary is that an object either is or is not a black hole, it does not depend on the observer. This means it does not depend on the velocity, for one can "fly by" an object at any velocity one likes (especially in a thought experiment, physically doing it may be slightly more difficult :-)).

#### pervect

Staff Emeritus
Gamish said:
OK, then let me ask this. What the heck is the purpose of a black hole? According to GR, if an object is so massive that objects are attracted to it by its gravitational force, at faster than c speeds, then the whole object will collapse on itslelf or something, so, does not matter and light travel faster than c in these black holes?
One might be able to think of an object falling into a black hole as moving at faster than light speeds in a certain manner - certainly the rate of change of it's position coordiante with respect to it's time coordinate is greater than 'c' in the Schwarzschild coordiante system, it is also true that light being emitted from an object falling into a black hole can't get out, and that the speed of the object reaches 'c' at the event horizon relative to an observer at infinity.

However, it's not usually thought of in that way, at least that's not the way I think of it. I think of the object as basically disappearing from our universe when it crosses the event horizion. At this point, the mass of the object can be considered to be added to the mass of the black hole.

The "loss of mass" can be considered to be a gradual process. I tend to think of it as the gain of the kinetic energy of the particle being compensated for by a loss of potential energy, so that the total energy (kinetic plus potential) of the system stays constant. This is not necessarily the best way of looking at it, but it's one of the simplest. One of the big problems with this approach is that it's not possible to localize the energy in the gravitational field as it is with the energy in (for example) the electromagnetic field, so it's a bit questionable to assign a meaning to the term "potential energy". In spite of these difficulties, that's how I visualize the process.

What is uniform for any approach is that the energy of the system (black hole + particle) remains constant. Actually this statement is only true when the energy can be defined in the first place, the existence of a defined energy in the standard manner requires that the system either be static, or has an asymptotically flat space-time. The standard definition(s) of the "energy of the system" involve more than simply adding up the energies of the parts when they interact with each other gravitatioanlly - because of this interaction, the total energy of the system is different from the sum of the energy of the parts.

#### pmb_phy

Gamish said:
If you travel faster than the speed of light, then your mass would become more than infinite (imposable), so, you would generate a gravitational field so large, that according to GR, you would open up a black hole. Is this true? My point here is not to prove that on can travel faster than c, as the numbers just don't add up.

Sometims, time runs too fast, time to :zzz:
If observer A is at rest in frame S observers your speed to increase then observer A will measure an increase in your mass and will also measure an increase in the strength of the gravitational field that you generate. However you will never become a black hole.

Its incorrect to assume something is a black hole because it has a certain amount of mass. E.g. a mini black hole has a mass of about that of Mt. Everest. However that mass is incredibly small compared to a neutron star, which is not a black hole.

Pete

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