Black holes

[dafydd]

But the speed of light is constant, so that teaching is right because when people write "speed of light" they mean the local speed oif light which is constant in GR.

You keep on demonstrating your inability to understand that the (local) speed of light is constant in GR while it is the coordinate speed of light that can vary (depending on the the coordinate system used).

By the beard of Flora McDonald, even I can understand that. I know more about physics than Farsight!

 

[W.D.Clinger]

It's your failure. You're clinging to teaching that contradicts what you can see and contradicts what Einstein said, and instead you're telling fairy stories about infalling space and neverneverland. Sorry if you find that boring. You are of course free to find entertainment elsewhere.

Where else can we watch a cage-fighter working out toddlers?

Speaking of which...

...The mathematical tools that are necessary for general relativity were readily available in the "absolute differential calculus"...all imaginable systems of co-ordinates...with respect to any substitutions whatever...any chosen system of reference...any system of co-ordinates...any substitution of the co-ordinates...independent of the choice of co-ordinates...any other system of co-ordinates...any choice of the system of co-ordinates...

In the opposing corner stands "ton of bricks" Farsight:

And according to Einstein we can assert that the Sun goes round the Earth? No. The general laws of nature are to be expressed by equations which hold good for all systems of co-ordinates does not give you carte blanch to declare that non-real solutions are real.

Whom should I believe, Einstein or Farsight?

I'm not going to believe Einstein just because he's famous, or because he won a Nobel Prize in physics, or because he's familiar with the relevant math, but it seems to me that the empirical evidence for Einstein's general theory of relativity really should count in Einstein's favor.

Farsight, on the other hand, is John Duffield of Poole.

Tough decision.

At the moment, I'm leaning toward Einstein. Farsight has provided absolutely no evidence in favor of FGR (Farsight general relativity) over standard GR (Einstein's general relativity). Furthermore, Farsight says FGR is entirely consistent with standard GR. That's untrue, and obviously so: Einstein said we can use any coordinate system we like, while FGR says we can't.

Because Farsight doesn't recognize that fundamental difference between FGR and standard GR, I'm inclined to doubt whether Farsight understands relativity as well as he thinks.

On the other hand, Farsight is John Duffield of Poole. Having a real name should count for something.

His opponents, after all, are a pack of anonymous nobodies: Albert Einstein, Hermann Weyl, Georges Lemaître, John A Wheeler, Kip Thorne, Charles Misner, Stephen Hawking, Steven Weinberg, Robert Wald, Clifford M Will, Matt Visser...

 

[Roboramma]

And yet people will tell you that in Einstein's theory of general relativity the speed of cogs is constant and the speed of light is constant. This doesn't affect the run-of-the-mill predictions, but it does affect our understanding of black holes and the universe, and our future direction in physics and cosmology.

Right, and you don't have any empirical evidence that contradicts that, given that what those people tell you predicts exactly the same results as what you are telling me.

 

[Reality Check]

And according to Einstein we can assert that the Sun goes round the Earth? No. The general laws of nature are to be expressed by equations which hold good for all systems of co-ordinates does not give you carte blanch to declare that non-real solutions are real.

And that is a total strawman or a result of ignorance, Farsight!

The "according to Einstein we can assert that the Sun goes round the Earth" is idiotic. According to the scientific evidence we (including Einstein) can assert that the Earth goes around the Sun.

According to every scientist since Newton we can select Earth centered coordinates in which the Sun goes around the Earth (ask NASA!).
According to Einstein, the laws of physics should be expressed in a way so that a change in coordinate system does not change the equations of physics.

 

[Brian-M]

But would you agree that, after adjusting for the changing distance-delay in seeing the light, to a stationary observer directly behind or before the moving ship the light on the moving ship appears to be moving slower than their own light?

I wasn't really happy with introducing a need to adjust for the changing distance delay when I wrote that. But just now I thought of a better way to describe the idea I was trying to convey.

Put the light clocks horizontal at different fixed heights from the "floor" inside a rotating space station, perpendicular to the direction of rotation. Since they're being held at different distances from the center of rotation (the hub), they're traveling at different speeds, which would mean that for an observer standing inside the space station, the light would appear to be bouncing back and forth at different rates exactly the same as in the GIF.

But going by Feynman's explanation for this, the light isn't actually traveling any slower. For someone floating beside the space station the light is clearly moving in a zig-zag pattern. The light in the clock closer to the hub is just zig-zagging over a shorter distance, so it reaches the opposite mirror sooner.

While for the observer inside the station, it appears that that the light is covering the same distance but moving at different speeds. To the observer inside the station it's indistinguishable from if the light in clock exposed to the higher "gravity" in the station were moving slower than the clock exposed to the lower "gravity" in the station, even though we know it really isn't.

(And I had been intending to point out this is also exactly what we observe with the same setup on a planet or near a black hole, and ask why the exact same observations with the exact same equipment in equivalent conditions should be presumed to be the result of different causes.)

ETA: The observer inside the station can see that the light is moving at different speeds, while the observer outside the station can see that it isn't. So someone assuming that the light is really moving at a different speed just because they can see it moving at a different speed isn't necessarily correct.

 

[ben m]

The "according to Einstein we can assert that the Sun goes round the Earth" is idiotic. According to the scientific evidence we (including Einstein) can assert that the Earth goes around the Sun.

According to every scientist since Newton we can select Earth centered coordinates in which the Sun goes around the Earth (ask NASA!).
According to Einstein, the laws of physics should be expressed in a way so that a change in coordinate system does not change the equations of physics.

Yep. Farsight really isn't good at this coordinates game.

In Sun-centered spherical coordinates, the Earth does NOT go "around" the Sun---what does that even mean? The Earth sits at a fixed theta, oscillates annually in r, and undergoes a constant increase in phi.

But, oh, right, if you transform that to Cartesian coordinates, yes, it's going around. Why do you want to translate to Cartesian? I have two answers to that.

The mainstream answer: in Cartesian coordinates, Newton's Laws are true---the second-time-derivative of your spatial coordinates is the same thing as the force. The first time derivative of your spatial coordinates is the same thing as specific momentum. So, if you've picked coordinates such that F= m d^2/dt^2 r, then you've picked Cartesian coordinates, and therefore the Earth's coordinates describe a circle around the Sun's.

But neither Cartesian coordinates, nor "time derivatives of coordinates go into laws of motions", are eternal truths of Nature. Cartesian-coordinates-plus-Newton is a *human convention*. The whole point of GR is that physics doesn't know what convention you are using, and so will work no matter how you do it. If you write down physical laws the way Einstein told you to ("generally covariant") rather than the way Newton told you to ("take derivatives of coordinate values"), then you no longer care what coordinate system you use. "The Earth oscillates up an down in r" is a physical-law-obeying geodesic in a Sun-centered spherical coordinate system. "The Earth sits at the origin and the Sun orbits it in the x-y plane" is a physical-law-obeying geodesic in an Earth-centered Cartesian coordinate system. "The Earth goes around the Sun-Earth barycenter" is a physical-law-obeying motion in one particular set of coordinate systems, i.e. the set where Newton's Laws work.

(What physical law are they obeying, if not Newton's Laws? Well, they're obeying a silly theory called General Relativity, in which the laws of motion are expressed in a generally-covariant way, under which "any coordinate system whatsoever" is valid.)

The other answer is: Farsight is transforming to Cartesian coordinates because he's unable to do anything else.

 

[Brian-M]

(And I had been intending to point out this is also exactly what we observe with the same setup on a planet or near a black hole, and ask why the exact same observations with the exact same equipment in equivalent conditions should be presumed to be the result of different causes.)

Ohhh. I just had an epiphany. A way to look at it that clearly shows that this doesn't just look like the same thing in gravity, but actually is the same thing.

A person in freefall in a gravitational field would be in the same situation as a stationary observer in freefall outside the previously described rotating space station, and the same situation as the observer in freefall watching the passing space-ship.

From his perspective, the light clocks would be flying up, up and away into space, just like the other light clocks aboard the space-station and/or spaceship. To him, the light in these clocks is also moving in a zig-zag pattern. When the "lower" clock passes him, it will be moving faster than the upper clock was, so the light has to travel further distance between mirrors, and so will take longer before bouncing off each mirror.

Someone in a fixed position relative the clocks may see the light in the bottom one as going slower, the same as happened on the space station, but like on the space station the light is "really" traveling a longer distance between the mirrors, which is something an observer in freefall can clearly see. Both literally and figuratively.

ETA: The epiphany being both that this extra distance traveled is in normal 3D space and not some fourth dimension like I was envisioning while turning Farsight's racehorse objection into an analogy, and by realizing that the person falling into the black-hole is stationary while everything else is zooming upwards, I now see why the space-being-sucked-in perspective makes sense, which I didn't really get before.

 

[Farsight]

It isn't like that Brian. You know how I said that if you panned across with your gedanken telecope watching the light go back and forth in the travelling observer's parallel mirrors? They're orthogonal to the direction of travel, so length contraction doesn't apply. Like Feynman said. The light is still moving at c, but now it looks slower to you, because your panning means you don't see travelling observer's lateral motion.

When you look at the lower of your two clocks in the gif, it doesn't look like it's going slower. And it isn't really travelling a longer distance. Again length contraction doesn't apply. It is going slower.

 

[Farsight]

But the speed of light is constant, so that teaching is right because when people write "speed of light" they mean the local speed of light which is constant in GR.

No, it's wrong, because we measure the speed of light using rods and clocks calibrated using the motion of light. We've been through all that with the NIST caesium fountain clock and the definition of the second and the metre.

You keep on demonstrating your inability to understand that the (local) speed of light is constant in GR while it is the coordinate speed of light that can vary (depending on the the coordinate system used).

Again, we've been through this. It doesn't matter what coordinate system you use, the light in the lower parallel-mirror light clock never gets to the end before the light in the upper clock. The exploding trains scenario removes any doubt.

 

[Farsight]

And yet people will tell you that in Einstein's theory of general relativity the speed of cogs is constant and the speed of light is constant. This doesn't affect the run-of-the-mill predictions, but it does affect our understanding of black holes and the universe, and our future direction in physics and cosmology.

Right, and you don't have any empirical evidence that contradicts that, given that what those people tell you predicts exactly the same results as what you are telling me.

This getting weird Robo. Suppose I show you two mechanical clocks which are identical in construction, only on one the hands are going round fast whilst on the other one they're going round slow. I can turn them both over and open them up and show you the moving cogs inside. One the first clock the cogs are whizzing around, on the second one the cogs are going round at a crawl. You don't then insist that the cogs are moving at the same speed, do you? You don't say you have no empirical evdience that they're moving at different speeds. It's the same for a light clock. Two identical optical clocks held at different elevations don't keep time. The lower clock goes slower. We could set up light beams and mirrors and reflectors in space at different distances from the earth. Then you really would be able to see the light going slower at the lower elevation. Again, don't dismiss the empirical evidence of what you can see because you believe in something that you can't see - for which there is no evidence at all.

 

[Farsight]

"The Earth sits at the origin and the Sun orbits it in the x-y plane" is a physical-law-obeying geodesic in an Earth-centered Cartesian coordinate system".

Which delivers the wrong understanding of what actually happens in this real universe. It's similar for black holes.

 

[edd]

OK. I'm curious about Farsight's response to this. We take clocks of whatever variety and give them to two observers - one who sits at a large distance from a black hole and one who bravely decides to go into freefall towards it.

The one at a large distance indisputably sees his friend's clock get redshifted slower and slower ever more as he falls in, until his clock appears from the outside to have stopped.

Farsight - what does the infalling observer see a distant clock do as he falls towards the event horizon, where you say he freezes and never passes through?

edit to add: to avoid ambiguity - the distant clock is directly overhead for the infalling observer

 

[Farsight]

Where else can we watch a cage-fighter working out toddlers?

Nowhere I suppose. But that is how it is, Clinger. I've bested you. You won't address the evidence or offer a counterargument, and your smokescreen of mathematics and snide comments is transparent. It only demonstrates your lack of sincerity as you try to protect your cargo-cult pseudoscience position on black holes:

"The black hole's gravity is so strong that it's pulling space itself into the central singularity faster than outwardly directed light can travel through that space".

Whom should I believe, Einstein or Farsight?

Both of us, because we're both saying the speed of light is not constant. And neither of us said that space is falling inwards in a gravitational field.

 

[DeiRenDopa]

"The Earth sits at the origin and the Sun orbits it in the x-y plane" is a physical-law-obeying geodesic in an Earth-centered Cartesian coordinate system".

Which delivers the wrong understanding of what actually happens in this real universe. It's similar for black holes.

Why is it "the wrong understanding of what actually happens in this real universe"?

Specifically, what objective, independently verifiable experiment(s) and/or observation(s) could you make - even if only in principle - that would show this to be "the wrong understanding of what actually happens in this real universe"?

And by "show" I mean which are quantitatively inconsistent with objective, independently verifiable predictions/explanations based on the theory ben m's short sentence is derived from.

 

[DeiRenDopa]

I somehow missed this; it deserves repeating ...

OK everybody, I think we've flogged this one to death and we aren't going to reach agreement, so let's call it a day.

I find it delightfully meta how Farsight often claims events in this thread have reached a standstill and yet they somehow manage to continue happening for those observing it.

 

[DeiRenDopa]

The exploding trains scenario removes any doubt.

No, it ... does ... not.

If someone takes the trouble to study what you've written, in an attempt to understand it; if they further think for themselves and do their own research; and if they write up, in some detail, an apparent contradiction in your idea (a pretty serious one, so it would seem), you do the cause of successfully communicating your idea to others great harm by persisting in ignoring them.

If this sort of non-response is typical of your posting behavior these last five years, it's really no surprise that you have failed so spectacularly. Assuming, that is, that your aim was - and still is - to at least get others to understand your ideas. Is that your aim?

 

[sol invictus]

Again, we've been through this. It doesn't matter what coordinate system you use, the light in the lower parallel-mirror light clock never gets to the end before the light in the upper clock. The exploding trains scenario removes any doubt.

It's nice when you make definite statements - rather than vague ill-defined claims - because they can actually be evaluated. As usual when you do so, they are wrong.

There is no reason in such an arrangement for the event A: "upper photon arrives at right side of lightclock" to be timelike separated from event B: "lower photon arrives at right side of lightclock". If the two events are spacelike separated, you can always choose a frame in which event B occurs first (for example, the rest frame of an observer moving at sufficiently high velocity in the correct direction). I have no idea what the "exploding trains scenario" is, but it apparently doesn't show what you think it shows.

 

[Farsight]

I find it delightfully meta how Farsight often claims events in this thread have reached a standstill and yet they somehow manage to continue happening for those observing it.

Ho ho. But I don't think there's much more mileage in it. Some of the other posters here are resorting to crybaby-loser emotional abuse, and I don't have time for it.

OK. I'm curious about Farsight's response to this. We take clocks of whatever variety and give them to two observers - one who sits at a large distance from a black hole and one who bravely decides to go into freefall towards it.

The one at a large distance indisputably sees his friend's clock get redshifted slower and slower ever more as he falls in, until his clock appears from the outside to have stopped.

No problem with that.

Farsight - what does the infalling observer see a distant clock do as he falls towards the event horizon, where you say he freezes and never passes through? edit to add: to avoid ambiguity - the distant clock is directly overhead for the infalling observer

This is an interesting one, we haven't really discussed it before now. Instead we've discussed the observer being at some fixed position X above the event horizon. At this location he's seeing the distant clock running fast and the light from it blueshifted. However because we have an infalling observer, he's moving away from the distant clock, meaning there's a running-slow redshift aspect too. These two factors tend to cancel each other out.

However there's yet another factor. We normally think of the infalling observer moving faster and faster and faster as he approaches the black hole. If say he was "dropped from infinity", he'd be moving "at the speed of light" at the event horizon. However the speed of light at the event horizon is zero, and he can't be moving faster than that. So he doesn't fall faster and faster. So at the end he sees the distant clock getting faster as his seeing slows down, and at some point he stops seeing. You might think it's like what happens when you fall asleep, but I fear it's more spectacular than that.

I need to get into non-accepted electron models to justify this spectacular, and since it's off-topic and I don't have patent evidence and Einstein to back me up, I'll leave it there.

 

[sol invictus]

Which delivers the wrong understanding of what actually happens in this real universe. It's similar for black holes.

So to you, a "wrong understanding" can make exactly the same set of predictions for every possible experiment that a "correct understanding" gives?

To the rest of us, if two "understandings" agree perfectly on every possible experiment one could ever perform, they are either both right or both wrong.

 

[edd]

So Farsight - you're saying he sees inbound light blueshifted?

Also I was under the impression this situation had been under discussion - I think there is very little disagreement if any about observers that are stationary at the horizon.