Faster than light travel

[tomBitonti]

Isn't Physics...pure physics...mostly a math driven thing? Thus, there are things that they can't even observe but which they can see the math predict which are theories.

In such a way, couldn't the math be part of the evidence regarding the interior of a black hole or special relativity?

well, math isn’t evidence. Math is how we organize evidence and create a tractable model for how things work. For black holes, my understanding is that it’s our past experience that guides us. Past experience says that physics doesn’t stop applying in places we can’t see. Then we don’t consider matter that has fallen outside of the visible universe because of cosmological expansion to have left the universe. Likewise, we expect physics to work more or less the same inside a black hole as outside. “Less” is mostly about what happens at the exact center, which has conditions that our understanding of physics can’t describe.
I was agreeing with Umbran’s second statement. (While setting it aside. I think it is irrelevant to my original point.) We can’t measure what happens inside a black hole. Strictly speaking, as an unmeasurable thing, it is not proper material for science.
Thanks!
TomB

 

[briggart]

well, math isn’t evidence. Math is how we organize evidence and create a tractable model for how things work. For black holes, my understanding is that it’s our past experience that guides us. Past experience says that physics doesn’t stop applying in places we can’t see. Then we don’t consider matter that has fallen outside of the visible universe because of cosmological expansion to have left the universe. Likewise, we expect physics to work more or less the same inside a black hole as outside. “Less” is mostly about what happens at the exact center, which has conditions that our understanding of physics can’t describe.
I was agreeing with Umbran’s second statement. (While setting it aside. I think it is irrelevant to my original point.) We can’t measure what happens inside a black hole. Strictly speaking, as an unmeasurable thing, it is not proper material for science.
Thanks!
TomB

There is no fundamental reason why matter falling outside the cosmological horizon would be lost to us forever, it depends on the nature of the current accelerated expansion phase. For all we know this could be temporary, similar to the primordial inflationary expansion, and if that is the case at some time in the remote future "we" will get back in touch with that matter. On the other hand, I don't think we have any reasonable idea of how we could get back in touch with matter inside a black hole horizon at all.

This doesn't really affect the overall discussion about FTL, black holes, etc., but there is some ground for looking at cosmological and black hole horizons in different ways.

 

[shawnhcorey]

There is no fundamental reason why matter falling outside the cosmological horizon would be lost to us forever, it depends on the nature of the current accelerated expansion phase. For all we know this could be temporary, similar to the primordial inflationary expansion, and if that is the case at some time in the remote future "we" will get back in touch with that matter. On the other hand, I don't think we have any reasonable idea of how we could get back in touch with matter inside a black hole horizon at all.

This doesn't really affect the overall discussion about FTL, black holes, etc., but there is some ground for looking at cosmological and black hole horizons in different ways.

Einstein's gravity states that the radial distance is increased to infinity. Since nothing can travel faster than light, anything that falls into a black hole will never reach the event horizon. It will fall forever.

This is one of the unresolved anomalies of black holes. Which is why some scientists are looking at alternatives.

 

[Umbran]

Isn't Physics...pure physics...mostly a math driven thing?

There is no such thing as "pure physics". No science is of value if it doesn't mix in, get its hands dirty, and actually demonstrate itself through experiment or observation of predictions.

Thus, there are things that they can't even observe but which they can see the math predict which are theories.

Beware of what you call "theory", for the common and technical uses vary. For people actually in the field, a "theory" is a model well established and tested by many high quality experiments. A model that has not been tested is an hypothesis.

Not that the world is consistent about this, but it is important. Einstein's General Relativity is referred to a a theory, because it has withstood a whole lot of testing. Meanwhile, so called "String Theories" have not, and are more properly considered hypotheses.

In such a way, couldn't the math be part of the evidence regarding the interior of a black hole or special relativity?

Mathematics can be an inspiration, sure. But a mathematical model is not "evidence".

 

[Umbran]

This is one of the unresolved anomalies of black holes. Which is why some scientists are looking at alternatives.

To quote Tyson - "The Universe is under no obligation to make sense to you."

It is less an anomaly, and more a thing that makes some physicists uncomfortable. Like mathematics, what makes you uncomfortable can be inspiration, but it isn't evidence.

 

[shawnhcorey]

To quote Tyson - "The Universe is under no obligation to make sense to you."

It is less an anomaly, and more a thing that makes some physicists uncomfortable. Like mathematics, what makes you uncomfortable can be inspiration, but it isn't evidence.

If an object is accelerated forever, it will gain infinite kinetic energy. This would violate the 1st law of thermodynamics. Black holes make me more than comfortable.

The universe does not have to make sense but science is making sense of the parts that we can.

 

[Umbran]

If an object is accelerated forever, it will gain infinite kinetic energy.

Sure, but that's a nonsensical statement, because "forever" is not an attainable moment. At any given time, it has finite KE.

Moreover, there's going to be a point in that descent in which the object fails to be a classical, or even relativistic object. Long before forever, it will spaghettify into bits that are better described as quantum objects, and that simple classical description will no longer hold. And, eventually, we'd expect that it would cease to be a separate object from the star that collapsed - the quantum objects having gained enough energy to do something like tunneling to the singularity, come into the region where spacetime is more like a quantum foam, or the like - and there's nothing to accelerate any more.

This would violate the 1st law of thermodynamics.

The Laws of Thermodynamics only hold for closed systems. The interior of a black hole is certainly open at the event horizon, and may well be open at the singularity.

 

[tomBitonti]

Einstein's gravity states that the radial distance is increased to infinity. Since nothing can travel faster than light, anything that falls into a black hole will never reach the event horizon. It will fall forever.

This is one of the unresolved anomalies of black holes. Which is why some scientists are looking at alternatives.

Well, what is the state of the universe at a particular time? Is it based on our awareness of an event based on when a signal from that event reaches us? Or do we consider that time has elapsed since the event created the signal that we perceived? The sense that there is a universal “now” doesn’t work in special relativity.
That said, I struggle with this same question.
It is true that we never see a crossing of the event horizon. The signal is stretched out over longer and longer time and red shifted away. But see the preceding paragraph.
Also, the infinite distance problem was, I thought, a problem of the coordinate system being used. A more careful choice of coordinate systems avoids infinities at the event horizon. (That is at the edge of my understanding. I’m thinking others could explain this last point better.)
Thanks!
TomB

 

[Umbran]

Also, the infinite distance problem was, I thought, a problem of the coordinate system being used. A more careful choice of coordinate systems avoids infinities at the event horizon.

So, spacetime at and across the event horizon is smooth. There is no physical discontinuity. Signals trying to escape to the distant stars get further and further red-shifted as you approach the event horizon, but that's not a physical infinity. It only seems like one to a distant observer.

The only real "infinity" in a black hole is at the singularity itself, which we don't get to look at.

 

[shawnhcorey]

Sure, but that's a nonsensical statement, because "forever" is not an attainable moment. At any given time, it has finite KE.

Moreover, there's going to be a point in that descent in which the object fails to be a classical, or even relativistic object. Long before forever, it will spaghettify into bits that are better described as quantum objects, and that simple classical description will no longer hold. And, eventually, we'd expect that it would cease to be a separate object from the star that collapsed - the quantum objects having gained enough energy to do something like tunneling to the singularity, come into the region where spacetime is more like a quantum foam, or the like - and there's nothing to accelerate any more.



The Laws of Thermodynamics only hold for closed systems. The interior of a black hole is certainly open at the event horizon, and may well be open at the singularity.

The pint is that the KE is forever increase, with no known source. That violates the 1st law.

The quanta cannot tunnel into the singularity. They are too far away. The probability of them doing so is almost zero.

The universe is a closed system because we can see a fixed distance into the past. All the energy we see back to the big bang is finite. Or would be if there weren't any black holes.

Well, what is the state of the universe at a particular time? Is it based on our awareness of an event based on when a signal from that event reaches us? Or do we consider that time has elapsed since the event created the signal that we perceived? The sense that there is a universal “now” doesn’t work in special relativity.
That said, I struggle with this same question.
It is true that we never see a crossing of the event horizon. The signal is stretched out over longer and longer time and red shifted away. But see the preceding paragraph.
Also, the infinite distance problem was, I thought, a problem of the coordinate system being used. A more careful choice of coordinate systems avoids infinities at the event horizon. (That is at the edge of my understanding. I’m thinking others could explain this last point better.)
Thanks!
TomB

The problem with the coordinate system is that a flat-space system is used. But space is not flat. It is impossible to get close to the event horizon. It is infinitely far away.

So, spacetime at and across the event horizon is smooth. There is no physical discontinuity. Signals trying to escape to the distant stars get further and further red-shifted as you approach the event horizon, but that's not a physical infinity. It only seems like one to a distant observer.

The only real "infinity" in a black hole is at the singularity itself, which we don't get to look at.

Signals from above the event horizon get red-shifted. There are no signals from the event horizon or below it. Nothing can escape the event horizon.