Black Holes and the Speed of Light

[Johnnyc]

This is my first post here but I've been reading this subforum for about a week. I was reading a thread that gave me a few ideas/questions. My questions are set up with quotes from the link below

http://forum.kerbalspaceprogram.com/index.php?/topic/146502-black-holes-spinning-faster-than-light/

Tullius Aug 25 2016
"In special relativity, the energy of an object is expressed as E = gamma*m*c^2 , where gamma depends on the speed (and increases to infinity, if the speed of the object approaches the speed of light), m is the mass of the object (in the classical sense) and c the speed of light.

Any particle that orbits a black hole orbits at a ridiculously high speed, which means that it has a ridiculously high energy.

The "relativistic mass" is defined as M = gamma*m. The advantage of this notion is that the famous E = M*c^2 holds also for moving particles and in general it simplifies the formulas. However, M is some kind of mass that depends on the speed of the particle in the reference frame of the observer"

Kerbiloid Aug 25 2016
"Does it mean that any particle, orbiting a blackhole, when reaching the event horizon gets infinity mass for an outside observer?"

Pb666 Aug 25 2016
"When they pass the event horizon, from our perspective universe, the particle ceases to exist and become part of the singularity."

Me
If we one day build a ship capable of hitting the speed of light, it would reach infinite relitavistic mass. Would that ship then become a singularity? 

Is it possible the speed of light is only a limit because anything moving faster transforms into a black hole?
 

Edited May 2, 2017 by Johnnyc

[Snark]

2 hours ago, Johnnyc said:

If we one day build a ship capable of hitting the speed of light

But we can't, because it's not possible.

2 hours ago, Johnnyc said:

it would reach infinite relitavistic mass

And this is why it's not possible.  To get infinite mass you'd need infinite energy, which you don't have.  If you could somehow grab the entire mass of the whole universe, convert it to pure energy, and pour all that energy into, say, one single electron... it still wouldn't be enough to accelerate the electron to c, because "a lot" < "infinite".  It would get really really really really close, but that's all.

2 hours ago, Johnnyc said:

Would that ship then become a singularity? 

Nope.  Because the situation can't happen in the first place.  Your question's a meaningless one; essentially what you're trying to ask is, "How would the laws of physics apply if the laws of physics didn't apply?"

2 hours ago, Johnnyc said:

Is it possible the speed of light is only a limit because anything moving faster transforms into a black hole?

No, the speed of light is a limit because everything's moving slower than that, and it gets asymtotically harder to go faster when you get closer to the speed of light, and it would take infinite energy to get there.  And since the universe doesn't have infinite energy in it, there's not enough energy for anything to do it, ever.

[Green Baron]

Totally ack. A body with a rest mass can not reach speed of light. Fullstop.

Relativistic mass is measured by how much it takes to change velocity or direction (eg. of a charged particle in a magnetic field). That's why energy (KeV) describes a speed.

The rest mass is what forms a singularity, not the relativistic mass. An observer travelling side by side at the same speed with a fast object would still measure just the rest mass. So, nope relativistic mass does not turn thing with a rest mass into points in space with infinite density (aka singularities) as they approach the speed of light relative to an observer at rest.

Only gravity does, the weakest of all forces in usual daylife.

Hope that's not totally wrong :-)

 

Edited May 2, 2017 by Green Baron

[Johnnyc]

Thanks for the response guys. I just thought it would be interesting/ironic if, say we do the un doable and we break the laws of physics and we are rewarded with compression into a singularity.

[Numerlor]

Why do you always shut down people with "Our rules of physics say it can't be so it is wrong" While it is most unlikely there are particles that can go faster than light there is a slight chance we don't know about them yet. For example dark matter and energy, what if it doesn't exist and our understanding of gravity is completly wrong?

This is a place to discuss not to shut down every one with things like that

Edited May 2, 2017 by Numerlor

[Green Baron]

What's eating you ? :-)

This place is titled science & spaceflight. When i answer i do so in compliance with the forum rules that forbid unproven claims. If someone asks a physics question i try to do my best to answer it from what i know, though i am aware that my knowledge is very limited compared to others as i am not a physicist. That is the discussion part.

If you know more, no problem, i am always eager to learn more. But if you do not accept basic physical principles then everything might be possible in your fantasy, including ftl and a different understanding of nature. This is not a problem, after all we are in a gameforum, as it is not science or spaceflight.

Problem is: if i may not answer with what a know from physics, what do want to hear ? Wild speculations ? Do you see any benefit in that ? What value would that have ?

Peace :-)

 

Edit: as others have pointed out in different threads on the same topic we need a theory that unites general relativity and quantum mechanics. That would shed more light on the singularity thing, though that light might be shed in vain as it does not return ;-)

Edited May 2, 2017 by Green Baron

[p1t1o]

@Johnnyc"relativistic mass" only exists in the reference frame of an observer. The passengers on the ship do not experience an increase in mass, nor can they detect any change in inertia of any objects. They do not collapse under their own gravitational pull as their mass approaches infinity.

This is the crux of "relativity", things change "relative" to something else. Consider the kinetic energy of a tennis ball. Stationary, its KE is zero. But the Earth is whipping around the sun at several thousand miles an hour. The KE of the tennis ball is measured relative to its reference frame, from another reference frame, say a heliocentric one, its KE can be completely different and almost unrelated to its KE measured in another frame.

So with relativistic mass.

Two co-moving masses at high relativistic speed will NOT start to gravitate towards each other (any more than they were before, anyway), because their relativistic mass is NOT increasing relative to one another.

A mass moving at high relativistic speed past a stationary object, however, will have a larger gravitational effect on said object than is described by its rest-mass alone.

Consider the relativistic mass of the stationary object from the perspective of the passengers on the ship though. From their perspective, the stationary object is moving past them at high relativistic speed. They will experience the "stationary" object having the increased mass and will experience its effects.

 

45 minutes ago, Numerlor said:

Why do you always shut down people with "Our rules of physics say it can't be so it is wrong" While it is most unlikely there are particles that can go faster than light there is a slight chance we don't know about them yet. For example dark matter and energy, what if it doesn't exist and our understanding of gravity is completly wrong?

This is a place to discuss not to shut down every one with things like that

An admirable statement, but it doesnt work quite that way when discussing such fundamental concepts as superluminal travel. It really is analogous to arguing that there is a slight probability that unicorns abound.

Dark matter and dark energy already are attempts to explain apparent gaps in our knowledge, we already know that our understanding of gravity is incomplete, not only are there whole, huge fields of science dedicated to just that (hence dark matter, dark energy) but the finer theory has even been recently revised to take into account discovered discrepancies at very low accelerations. The light speed limit also, explains AN UNIMAGINABLE amount of stuff - tinkering with the idea that superluminal travel just might be possible, digs a rather large whole in all of the underlying physics that you'd also have to explain. You cant just rely on the wiggle-room in less-than-absolute-proof, because almost our whole body of science agrees that it must be a rule.

If you attempt to explain what happens to a superluminal particle, with our current science, it gives you garbage results that cannot be translated to reality. You cant just say "but what if it did?" because there is no body of knowledge to explain it. Literally the only thing you can say is "But what if it did?" and after that, you are free to make things up - hence, its not much use in scientific discourse.

tl;dr - there is not much that is certain in the universe, but as far as things go, the lightspeed limit and the laws of thermodynamics are about the most certain concepts in the entirety of human knowledge.

 

Edited May 2, 2017 by p1t1o

[KSK]

4 hours ago, Numerlor said:

Why do you always shut down people with "Our rules of physics say it can't be so it is wrong" While it is most unlikely there are particles that can go faster than light there is a slight chance we don't know about them yet. For example dark matter and energy, what if it doesn't exist and our understanding of gravity is completly wrong?

This is a place to discuss not to shut down every one with things like that

Because there's a slight chance of anything you care to imagine. For adequately small definitions of 'slight'. Going down that route tends to stifle any rational debate because whatever reasonable comments people put out are invariably met with yet another tiresome rendition of 'well it might be possible and we just don't know about it yet', aka 'science doesn't know everything therefore I choose to ignore anything I don't personally agree with.'

As seen many, many times on this particular forum.

[Numerlor]

20 minutes ago, KSK said:

 aka 'science doesn't know everything therefore I choose to ignore anything I don't personally agree with.'

As seen many, many times on this particular forum.

I was just implying that this is a place to discuss, he wanted to discuss if something at speed of light would become a black hole of it's own. First answer that came was it can't be done. I'm not saying it can be done but I'm not saying it can't be done, we are just scratching the surface of quantum physics with which there theoretically could be negative mass leading to possible ftl speeds of some kind. But I don't know, I just play kerbal not study this.

Edited May 2, 2017 by Numerlor

[Steel]

10 minutes ago, Numerlor said:

I was just implying that this is a place to discuss, he wanted to discuss if something at speed of light would become a black hole of it's own. First answer that came was it can't be done. I'm not saying it can be done but I'm not saying it can't be done, we are just scratching the surface of quantum physics with which there theoretically could be negative mass leading to possible ftl speeds of some kind. But I don't know, I just play kerbal not study this.

Even these FTL ideas floating around don't break the speed of light "properly", they're workarounds that still obey GR, so the question is still complete nonsense.

[sevenperforce]

It is nonsense, but I think it's instructive to explain why it's nonsense, and why the underlying question doesn't close.

The speed of light isn't a speed limit; it's the relationship between space and causality. Time and space are linked dimensions, and you are only able to move through one of them at any given point. Light is something that essentially has infinite speed because it matches the rate of casuality; it's mathematically nonsensical to imagine something going faster than the rate of causality because it would then become its own cause.

[KSK]

20 minutes ago, Numerlor said:

I was just implying that this is a place to discuss, he wanted to discuss if something at speed of light would become a black hole of it's own. First answer that came was it can't be done. I'm not saying it can be done but I'm not saying it can't be done, we are just scratching the surface of quantum mechanics with which there theoretically could be negative mass leading to possible ftl speeds of some kind. But I don't know, I just play kerbal not study this.

No - the first answer he got was 'it is not possible' and this is why. That allowed for further discussion of the facts, including correction of or elaboration of those facts as required. Vague assertions that 'we're only scratching the surface of quantum mechanics...' don't add anything much to the discussion. At least not without appealing to bucketloads of maths that very few people on this forum - myself included - are equipped to deal with.

At which point, the discussion almost invariably descends to people flinging analogies at each other, none of which really work very well.

Anyway - I'm not adding much to the original discussion either now, so I'll duck out. The first few posts gave OP some good answers anyway.

Edited May 2, 2017 by KSK

[HebaruSan]

If I'm not getting my wires crossed here, the "It's impossible" responses may be missing the point.

The question, "Can an object travel fast enough to collapse into a singularity?" does not depend on infinite mass, because you don't need infinite mass to form a singularity. A star that collapses into a black hole only ever has finite mass, so FTL is a red herring of sorts. The question can be asked for speeds less than c, in which case the answers about rest mass vs relativistic mass are the ones that are pertinent.