# Mass increase from high velocity Q

#### TheTechNoir

Hi folks, I'm brand new here... never been a part of a physics forum before and I'm just an amateur I have no professional or academic background hah most is a grade 10 "science" course (a unit on bio, unit on chem, unit on physics not even specified and barely touched physics).

Anyways that's my introduction
Out of nowhere today a light bulb went off and I was curious about something. If you were to go for example at 0.99999999c in a spacecraft I understand that your mass would increase largely relativistically. Now I am wondering, would it be possible to reach a sufficiently high percentage of the speed of light to reach critical mass with a finite mass and thus gravitationally collapse and form a black hole? Or would that require light speed (infinite mass) which is obviously impossible. Also, if it were possible (hypothetically - I know having the energy required to reach this potential speed would most likely be completely implausible) what would happen, I mean if to the Earth's perspective you collapsed into a black hole how would that work if you were a black hole from some perspectives and not others?

Thanks if anyone can help me, I am ASSUMING it would not be hypothetically possible but the thought still struck me as worth asking.

Related Special and General Relativity News on Phys.org

Mentor

#### jcsd

Gold Member
Hi folks, I'm brand new here... never been a part of a physics forum before and I'm just an amateur I have no professional or academic background hah most is a grade 10 "science" course (a unit on bio, unit on chem, unit on physics not even specified and barely touched physics).

Anyways that's my introduction
Out of nowhere today a light bulb went off and I was curious about something. If you were to go for example at 0.99999999c in a spacecraft I understand that your mass would increase largely relativistically. Now I am wondering, would it be possible to reach a sufficiently high percentage of the speed of light to reach critical mass with a finite mass and thus gravitationally collapse and form a black hole? Or would that require light speed (infinite mass) which is obviously impossible. Also, if it were possible (hypothetically - I know having the energy required to reach this potential speed would most likely be completely implausible) what would happen, I mean if to the Earth's perspective you collapsed into a black hole how would that work if you were a black hole from some perspectives and not others?

Thanks if anyone can help me, I am ASSUMING it would not be hypothetically possible but the thought still struck me as worth asking.
Look at it this way: your speed is relative so you can always find a frame where you are travelling at an arbitarily large proper fraction of c, but black holes are not relative they're a specific set of soltuions to Einstein's field equations. The gravitational singularity in a balck hole cannot be done away with by choosing a different frame of reference.

So simple arguments from consistency demand that a massive observer travelling at large fractions of c cannot turn in to a black hole.

#### TheTechNoir

Look at it this way: your speed is relative so you can always find a frame where you are travelling at an arbitarily large proper fraction of c, but black holes are not relative they're a specific set of soltuions to Einstein's field equations. The gravitational singularity in a balck hole cannot be done away with by choosing a different frame of reference.

So simple arguments from consistency demand that a massive observer travelling at large fractions of c cannot turn in to a black hole.
I read the previous link provided so I have an idea and I do know it cannot be so.

But in regards to your response (don't take this as me arguing against you or saying you're wrong) I realize that you can always find someone traveling very close to c from certain frames of reference but doesn't it make a difference whether they are traveling in force-free constant velocity motion or accelerating?
I don't mean this to dispute your post as I realize it is correct in relation to my original question as a reason for why the black hole is different and could not be created in that manner.
Thanks a lot btw both of you for the answers :)
I have a feeling if I look through this forum enough I can learn quite a lot to supplement my beginner reading (admittedly just reading things like the elegant universe or michio kaku's laymen intended books, etc. at the moment pretty new to this)

#### jcsd

Gold Member
I read the previous link provided so I have an idea and I do know it cannot be so.

But in regards to your response (don't take this as me arguing against you or saying you're wrong) I realize that you can always find someone traveling very close to c from certain frames of reference but doesn't it make a difference whether they are traveling in force-free constant velocity motion or accelerating?

I don't mean this to dispute your post as I realize it is correct in relation to my original question as a reason for why the black hole is different and could not be created in that manner.
Thanks a lot btw both of you for the answers :)
I have a feeling if I look through this forum enough I can learn quite a lot to supplement my beginner reading (admittedly just reading things like the elegant universe or michio kaku's laymen intended books, etc. at the moment pretty new to this)
Well you can pretty much always choose bad* cooridinates, for example Rindler coordinates in flat sapcetime, which create a horizon like the event horizon that occurs in Schwarzschild coordinates in Schwarzschild spacetime. But these two coordinate singularities (the Rindler horizon and the event horizon in Schwarzschild cooridnates) come from extending (the) coordinate systems a bit farther than you really oughta.

The gravitational singularity at the centre of a black hole is a property of the spacetime which it sits in rather than any property of a coordinate sysetm that you might choose to map that spacetime with so you cannot make one appear or disappear by changing your frame of reference. So a balck hole is not a frame effect so cannot be created by viewing an object in a different frame of reference.

*I use the term 'bad very loosely as what is bad for one purpose may be good for another.

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving