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# Is mass also relative?

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If I am not mistaking the faster an object is going the higher it's mass will become, but this has to be relative to something right? If two objects are going at 0.8 c in the same direction they don't see the other moving at all, so their perception of the other mass should remain the same, right? However to a stationary observer both of the moving objects masses would increase?

If this is true then I have a question concerning of this and back holes, but lets leave it at this for the moment.

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If I am not mistaking the faster an object is going the higher it's mass will become, but this has to be relative to something right? If two objects are going at 0.8 c in the same direction they don't see the other moving at all, so their perception of the other mass should remain the same, right? However to a stationary observer both of the moving objects masses would increase?
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Okay, now moving on. If an object is moving fast enough will its mass turn so large that is collapses into a black hole?

The problem that I see here is that for the stationary observer the objects mass will be large enough to turn into a black hole (assuming this happens) but to another (something moving at half the speed of the primary object) it will not.

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The part you are missing is the whole relative part. Imagine your relatively superfast object, with a very large mass relative to you. All the atoms masses are the same relative to each other, just not to you, so they arent going to collapse.

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Okay, now moving on. If an object is moving fast enough will its mass turn so large that is collapses into a black hole?
Much less simple and intuitively obvious answer: not as perceived by an observer in the object’s frame. To that observer, at a sufficient relative velocity, the rest of the universe becomes so massive that the gravitational force it exerts on objects in the observer’s frame become very large, like those of a black hole on objects with small relative velocities. To an observer in the frame of the rest of the universe, the objects in the first observer’s frame become so massive that the gravitation force it exerts on objects near it become very large, like a black hole.

It’s important to note that, although somewhat like a black hole to various observers, the universe and the objects are not exactly like or indistinguishable from ordinary black holes. It’s also worth noting that this scenario is likely completely hypothetical – AFAIK, if could result from no natural process, and is very unlikely to be realized by any artificial means. It is, however, possible in principle.

The problem that I see here is that for the stationary observer the objects mass will be large enough to turn into a black hole (assuming this happens) but to another (something moving at half the speed of the primary object) it will not.
Correct.

The key to resolving these seeming paradoxes is to calculate precisely what is observed by any observer in which you’re interested, keeping in mind that the passage of time and the simultaneity and sequence of events perceived by these observers differ. Such an exercise isn’t trivial. I’ve personally not completed one, nor read of it, so to some extent, I’m speaking without supporting evidence, conjecturing based on my understanding of the principles of relativity theory.

It’s also, IMHO, important to note that relativity is not necessarily a correct theory. Although superbly confirmed by the fairly narrow range of natural and artificial physical phenomena observed to date, it may fail in more extreme scenarios such as the above.

We wouldn’t want physics to get boring, eh? :shrug:

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So basically we don't know exactly what happens in these extreme events jet?

Well that's quite understandable, as physics are not 100% accurate jet.

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So basically we don't know exactly what happens in these extreme events jet?

We can never know exactly what happens in any event. :confused:

physics are not 100% accurate jet.

I don't think it will ever be 100% correct either. That would require us to understand everything about the universe, including it's origins.

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We can never know exactly what happens in any event. :confused:

hehe.. I love this argument.

I could respond to that with this: We can never know if we can ever know exactly happens in any event... and we can never know if that is true either.

Wouldn't you agree? :confused:

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I don't think it will ever be 100% correct either. That would require us to understand everything about the universe, including it's origins.
Even if we managed that, there would still be the uncertainity principle...
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Even if we managed that, there would still be the uncertainity principle...

I'm not so sure about that. B)

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hehe.. I love this argument.

I could respond to that with this: We can never know if we can ever know exactly happens in any event... and we can never know if that is true either.

Wouldn't you agree? :eek:

As far as our current theories of physics are constructed, there is a bias towards uncertainty: that we would need to know all variables involved in any measurement to a degree that goes beyond what we are able to measure, AND that the very act of making observations at this level causes interaction between the observer and the observed.

For a more clever explanation: B)

Uncertainty principle - Wikipedia, the free encyclopedia

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