Black holes

[Complexity]

[lurker off]Cute. You've got a spelling error in the image, though: "beteen".

I've been enjoying the discussion here, although some of the explanations are over my head. Still, though, I don't understand what Farsight is getting at: how does this effect, which is completely congruent with relativity theory, disprove relativity? It seems it's central to his complaint. Why is it so important?

[/lurker on]

As far as I can tell, Farsight doesn't understand enough to appreciate your very correct point.

If he admitted as much, then he wouldn't have any point, and where's the fame in that?

 

[ben m]

Brian-M, thanks for the Feynman quote. It illustrates a particular aspect of physics crackpottery. Farsight has been showing us his light-clock diagram as though it's a trigger to do think about something new. "Think about a light clock in a gravity field. Bet you've never done that before! Start there and I'm sure you'll draw my conclusions yourself."

It's worth emphasizing that that light-clocks have been standard gedanken-experiment fodder for 100 years. It's nice to see it from Feynman in particular, because it gives me an excuse to quote him:

The first principle is that you must not fool yourself—and you are the easiest person to fool. So you have to be very careful about that. After you’ve not fooled yourself, it’s easy not to fool other scientists.

 

[DeiRenDopa]

It doesn't matter where I am, the lower beam gets to the end faster than the upper beam.

Here's an example where the lower beam gets to the end faster than the upper beam:

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And here's an example where the upper beam gets to the end faster than the lower beam:

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The lower beam is the same in both cases, but the upper beam is different. However, in both cases the upper beam is at a greater elevation than the lower beam. Both these are Farsight signature diagrams.

How is this possible?!?

It doesn't appear to travel at a different speed. It travels at a different speed.

Yep, and not just one particular different speed ... light travels, in FGR (Farsight GR), at as many different speeds as you care to name*.

And clocks don't clock up the flow of time. They clock up some kind of regular cyclic motion. That's all they do. That's what they all do.

For those who have been following only this thread, Farsight posted this idea (that clocks "clock up some kind of regular cyclic motion. That's all they do. That's what they all do.") on another thread, and a discussion of his claim ensued. Here is as good as any a post to start reading that discussion.

You'll see that he bailed out before the discussion reached any conclusion; perhaps he'll continue it here?

Here, for example, is one exchange that Farsight walked away from:

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me: What is the "regular cyclic motion" in a muon clock?

Farsight: It's called spin. The muon has a magnetic moment.

me: It does. Where's the motion?

Farsight: In the muon. You need to read up on magnetic moment, Dopa. Here, try this. Once the muon decays the motion is apparent. Note however that this is wrong: "There simply is no internal structure of the electron that will explain its properties!". It's one of those fables I'm afraid.

me: Here's my muon, just sitting there. Suddenly, whoosh, no more muon. What was moving, in the muon, before it decayed?

Farsight: Stress-energy.

me: Huh? I have no idea what this means. Would you be kind enough to explain, in some detail please?
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Why is this relevant to this thread? Well, one reason is Farsight's unusual ideas concerning time and clocks (that clocks "clock up some kind of regular cyclic motion). The fact that all local clocks - no matter how they work when you turn them over, unscrew the backs, and look inside to reveal the mechanism (as Farsight says) - tell the same time means, per Farsight, that there's "regular cyclic motion" somewhere in that mechanism.

Now if you do your own research, and think for yourself (as Farsight suggests), you'll discover that the "spin" of the muon (to take one example) is not the same as classical angular momentum. In fact, there's a theory in physics which accounts for it (the muon magnetic moment) extraordinarily well. A theory associated with Feynman, whose name has come up here recently; it's called Quantum Electrodynamics (QED), and is the most precise theory in physics today. In that theory, the muon's magnetic moment is not due to anything moving.

Oops.

* you are naming the number of different speeds, not the speeds themselves; you can say you want 25 different speeds, or 1,234,567,890 different speeds (all for the same beam) ... but you don't get to choose any speed itself (i.e. you cannot say "I want 10 billion mega-parsecs per second", for example, or "I want 1 nm per giga-year")

 

[Farsight]

I was sick of seeing that tired old uninteresting diagram since long before DeiRenDopa started reposting it. To liven things up a little, I've made an animated GIF version that comes with an explanation...

I hope you appreciate it Farsight. Just right click on it and select "Save Image As" to save it to your computer. Then you can upload it to your own JREF photo album like I did and link to it in your posts like I did here. Or stick it on a web-page. Or add it to posts as an attachment. Whatever you want.

ETA: I thought you might like to know that the reason for the background gradient is to represent close proximity to a black hole by means of darker shades.

Good stuff Brian, thanks.

 

[Farsight]

Farsight, I was looking through Six not-so-easy Pieces by Richard Feynman, and I found something in the article on Special Relativity that has me wondering how your "speed of light changes" theory would apply...

No problem. I'm a bit of a Feynman fan as it happens. He was known as "The Great Explainer" and said things like "the first principle is that you must not fool yourself, and you are the easiest person to fool".

I'd like your thoughts about it. Here's the relevant text, typed in exactly as it is in the book...

OK. I'll put my comments in black.

This slowing of the clocks in a moving system is a very peculiar phenomenon, and is worth an explanation. In order to understand this, we have to watch the machinery of the clock and see what happens when it is moving. Since that is rather difficult, we shall take a very simple kind of clock. The one we choose is rather a silly kind of clock, but it will work in principle: it is a rod (meter stick) with a mirror at each end, and when we start a light signal between the mirrors, the light keeps going up and down, making a click every time it comes down, like a standard clicking clock. We build two such clocks, with exactly the same length, and light always travels with speed c.

This is the parallel-mirror light clock as used in the Simple inference of time dilation due to relative velocity. I've referred to it before. The Lorentz factor comes from Pythagoras' theorem. The base of a right-angled triangle is your speed as a fraction of c, the hypotenuse is the light path where c=1 in natural units, and the height is the Lorentz factor, with a reciprocal distinguishing length contraction and time dilation.

We give one of these clocks to the man to take along in his space ship, and he mounts the rod perpendicular to the motion of the ship; then the length of the rod will not change. How do we know that perpendicular lengths do not change? The men can agree to make marks on each other's y-meter stick as they pass each-other. By symmetry, the two marks must come at the same y- and y'-coordinates, since otherwise, when they get together to compare results, one mark will be above or below the other, and so we could tell who was really moving.

Fine. This is standard special relativity.

Now let us see what happens to the moving clock. Before the man took it aboard, he agreed that it was a nice, standard clock, and when he goes along in the space ship he will not see anything peculiar. If he did, he would know he was moving—if anything at all changed because of the motion he could tell he was moving. But the principle of relativity says this is impossible in a uniformly moving system, so nothing has changed. On the other hand, when the external observer looks at the clock going by, he sees that the light, in going from mirror to mirror, is "really" taking a zig-zag path, since the rod is moving all the while. We have already analyzed such a zig-zag motion in connection with the Michelson-Morley experiment. If in a given time the rod moves forward a distance proportional to u in Figure 3-3, the distance the light travels in the same time is proportional to c, and the vertical distance is proportional to √(c² - u²).

As above, I've talked about this previously, saying that we see the light going like this /\/\/\ whilst the guy see his own light going like this ǁ.

That is, it takes a longer time for light to go from end to end in the moving clock than the stationary clock. Therefore the apparent time between the clicks is longer for the moving clock, in the same proportion as shown in the hypotenuse of the triangle (that is the source of the square root expressions in our equations). From the figure it is also apparent that the greater u is, the more slowly the clock appears to run. Not only does this particular kind of clock run more slowly, but if the theory of relativity is correct, any other clock, operating on any principle whatsoever, would also appear to run slower, and in the same proportion—we can say this without further analysis. Why is this so?

Strictly speaking special relativity talks about relative motion with no privileged frame, but I have no problem with the above. Feynman is crystal clear. The phrase longer time is quite an interesting one as it happens. Here we've got a clock using moving light. What's actually longer is the light-path length. This: / is longer than this: | .

To answer the above question, suppose we had two other clocks made exactly alike with wheels and gears, or perhaps based on radioactive decay, or something else. Then we adjust these clocks so they both run in precise synchronism with our first clocks. When light goes up and back in the first clocks and announces it's arrival with a click, the new models also complete some sort of cycle, which they simultaneously announce by some doubly coincident flash, or bong, or other signal. One of these clocks is taken into the space ship, along with the first kind. Perhaps this clock will not run slower, but will continue to keep the same time as it's stationary counterpart, and thus disagree with the other moving clock. Ah no, if that should happen, the man on the ship could use this mismatch between the two clocks to determine the speed of his ship, which we have been supposing is impossible. We need not know anything about the machinery of this new clock that might cause this effect—we simply know that whatever the reason, it will appear to run slow, just like the first one.

All good stuff. Feynman might have mentioned say a quartz wristwatch or pair production & annihilation here, or even The Strange Theory of Light and Matter to get across how other clocks are similarly affected. That would have given some cause rather than just relying on principle. But OK, he's just telling us about SR, no issue.

Now if all moving clocks run slower, if no way of measuring time gives anything but a slower rate, we shall just have to say, in a certain sense, that time itself appears to be slower in a space ship. All the phenomena there—the man's pulse rate, his thought processes, the time he takes to light a cigar, how long it takes to grow up and get old—all these things must be slowed down in the same proportion, because he cannot tell he is moving.

All the phenomena are slowed down. No problem with that. People call this time dilation and say time is slower. But it's the processes proceeding at a slower rate. The local rate of all motion is reduced because of the macroscopic motion through space. If the guy in the spaceship was travelling at c (he can't actually do this but nevermind) then there is no local motion.

I'd like your thoughts about the speed of light on the moving space ship. Has it slowed down or not?

No it hasn't. It's still c, like Feynman said. It's just travelling a zig-zag path. Note however that if you had a supergedanken telescope, and if you panned across the sky with it watching the traveller's parallel-mirror light clock, you'd see the light apparently moving like this ǁ at a slower rate than your own.

Also, what do you think of that final paragraph?

It's OK. He didn't say time is flowing slower or passing slower, which is good.

 

[ctamblyn]

Now that Farsight's done a runner, this thread can go back to normal and we can certainly continue to discuss that if you like.

Basically, it works to the extent that rivers can be described by the right kind of idealized fluid equations - which is up to a point. Ultimately water is made out of molecules and so doesn't obey continuum equations. That means, in the language of relativity, that various higher-order corrections to the equations break "Lorentz invariance" (rather, the symmetry that's like Lorentz invariance but based on the speed of sound rather than light).

But at leading order it really is a very good analogy.

sol, thank you and I apologise for abandoning the thread (real life got in the way I'm afraid).

My first exposure to the river model for black holes was this paper, which I found a few years back while trying to write some code (mostly for personal amusement) to generate animations of dust clouds moving around non-rotating black holes; specifically, I was looking for less CPU-intensive ways of producing the geodesics. As it turned out, there were better methods.

That was some time ago and I haven't thought about it since, but this thread rekindled my interest. The paper shows how it can be extended to work with rotating black holes, but what I wondered is: can it usefully be extended to a much wider class of solutions? Is it too much to ask that a similar model would work for any vacuum solution, for example?

Perhaps this is a difficult question, perhaps not; I lack the knowledge to tell at this stage . Actually, even if you could just recommend some reading material to get me started I'd be very grateful.

 

[Farsight]

...how does this effect, which is completely congruent with relativity theory, disprove relativity? It seems it's central to his complaint. Why is it so important?

It doesn't disprove relativity at all. It's important because people say "relativity tells us X" when they're contradicting what Einstein actually said.

 

[ctamblyn]

Farsight - do you ever intend to answer this question?

All I am asking for is emprical evidence that favours FGR over "MTW" GR. Any progress on that? Because so far, the stuff you have cited has been entirely consistent with "MTW" GR.

Note: this clearly calls for empirical evidence that is inconsistent with "MTW" GR, while being consistent with FGR.

 

[Farsight]

It really does matter where the 'distant observer' is, Farsight. The information about the clock ticking has to leave the clock and reach that location, and that's where the difference lies.

Honestly edd, it doesn't matter. What happens happens. What doesn't doesn't. There's never any contradiction about that. There's been stuff in the past about say an elephant in two places at once, but it's misguided. The best way to appreciate this is to replace the light beams with trains. The first one to hit the buffers detonates a bomb on the other one. It's always the lower train that blows up. Your motion and your distance affects the way you see things, but you don't see the upper train blow up.

Those of us who agree with the textbooks think an infalling object passes through the horizon in finite proper time, but the time for photons from that object to escape diverges. You think that the infalling object freezes because the photons from that object take longer to escape.

Not quite. I think the infalling object freezes because the speed of light goes to zero where the textbooks say gravitational time dilation goes infinite.

It's not just about what the clock is doing - what the signal from the clock is doing and how long it takes to get to the observer is crucial to the whole discussion and glossing over this is a very dangerous thing to do.

See above, if you're not happy press me some more on it. Meanwhile note this: what's glossed over is why the light doesn't get out. A vertical beam emitted at the event horizon doesn't slow down, it doesn't curve round, it doesn't fall back, and it isn't fighting like a salmon in some "waterfall" of infalling space.

 

[Farsight]

...That's three different values for c.

...We're up to four now...

...Conclusion: using the Farsight method, the speed of light at any location can have many different values, simultaneously. It all depends on which clock you choose as your standard ...

Nope. You just look at the two light clocks. The lower clock runs slower than the upper clock because the light's going slower there:

Conclusion: what you don't do is try to hide the obvious with obviously facile assertions. People aren't that stupid.

 

[Guybrush Threepwood]

Meanwhile note this: what's glossed over is why the light doesn't get out. A vertical beam emitted at the event horizon doesn't slow down, it doesn't curve round, it doesn't fall back, and it isn't fighting like a salmon in some "waterfall" of infalling space.

So if I'm sitting on the event horizon, and I sellotape two torches together so one points up and one points down, and turn both on, what happens to the light from the torch pointing down?

 

[Ziggurat]

Conclusion: what you don't do is try to hide the obvious with obviously facile assertions. People aren't that stupid.

Who are these people of whom you speak?

Because so far, pretty much everyone BUT you agrees with DRD. And you agree with... nobody. Oh, sure, you claim Einstein agrees with you (by conveniently ignoring all the times he contradicts you), but don't you find it the least bit curious that nobody who's actually alive seems to be taking your side? Granted, the popularity of an idea doesn't prove its correctness or incorrectness, but why is it that you are unable to marshal any support from anyone else for your position? Even if you are the misunderstood genius you imagine yourself to be, what is it about your communications skills which so constantly fail to convince anyone?

Aren't you even the least bit curious?

 

[sol invictus]

The paper shows how it can be extended to work with rotating black holes, but what I wondered is: can it usefully be extended to a much wider class of solutions? Is it too much to ask that a similar model would work for any vacuum solution, for example?

I think that is too much to ask. For instance, I doubt that fluids can support the analog of time-varying gravitational waves, because sound waves aren't spin-2.

Perhaps this is a difficult question, perhaps not; I lack the knowledge to tell at this stage . Actually, even if you could just recommend some reading material to get me started I'd be very grateful.

Here's a very recently updated review^*.

^*Note to Farsight - this review is by Visser et al, and received a significant update in May 2011. What was that nonsense about how Visser had "moved on"?

 

[ctamblyn]

I think that is too much to ask. For instance, I doubt that fluids can support the analog of time-varying gravitational waves, because sound waves aren't spin-2.

Sorry, yes, that should have been immediately obvious.

Here's a very recently updated review^*.

That's perfect, thank you sol!

^*Note to Farsight - this review is by Visser et al, and received a significant update in May 2011. What was that nonsense about how Visser had "moved on"?

 

[Farsight]

I didn't conflate distance and displacement, you did. You said it was a square carpet. But how can you know it's square unless you also know the direction of each length? How can you know anything at all about its shape, or its area, with only a length? Obviously, you cannot. You need a displacement, or you won't get a square. Never once have you tried to explain how you can get a square without a displacement....

I told you it didn't matter what shape it was, you cannot draw any object with n edges where the edge lengths are less than zero. I gave you the example of a 3 4 5 triangle, and still you try to defend the negative carpet.

All: see page 13 for the background to this.

That's the real dishonesty here: your refusal to actually engage in debate.

Surreal. Just look at the thread.

But that prospect was pretty obviously doomed once you started claiming "math isn't real".

I said some solutions are non-real. Here it is again. I was careful to make the distinction between distance and displacement:

"I'm afraid D'rok, that that description is almost totally accurate. The only thing I think it's worth pointing out is that some of the people here are mathematicians rather than physicists. There's nothing wrong with mathematics, and it's a vital tool for physics, but IMHO some people involved in physics sometimes attach more importance to mathematics than patent scientific evidence. What I'm trying to get across here re black holes concerns "non-real" solutions. For example if you need to carpet a square room which has a floor area of 16m², you can employ mathematics and work out that you need a carpet measuring 4m by 4m. However there is another solution to √16, namely -4. Mathematics does not tell you that a carpet measuring -4m by -4m is a non-real solution. It doesn't tell you that such a "negative carpet" does not actually exist. Whilst there's no problem with a negative displacement, distance is a scalar, and there is no such thing as a negative distance".

That's the sine qua non of the physics crank.

I'm no crank. And I know my stuff. But you are abusive, so we're done Zig. I'm not wasting any more of my time on you. I refuse to "engage in debate" with you any more.

 

[Farsight]

Not to forget; found out they didn't understand the universe/world/women, fell in love, built a siege catapult, read books, fell out of love, built a laser¹, made friends they'd still know twenty years later, organise a conference, read more books, make DDT, participate in a riot, found the love of their life..........

Not to forget... had another child.

 

[dafydd]

I'm no crank

I beg to differ.

 

[DeiRenDopa]

The best way to appreciate this is to replace the light beams with trains. The first one to hit the buffers detonates a bomb on the other one. It's always the lower train that blows up. Your motion and your distance affects the way you see things, but you don't see the upper train blow up.

Really?

Let's take the two clocks trains separated by ~0.3 m in elevation (or vertically, if you prefer), in a room, in a lab. Not in freefall.

That's the optical clock-based experiment you have mentioned many times in this thread.

How does the bomb on the lower train know the upper train has hit its buffer?

For example, does the buffer send a flash of light (or radio, or gammas, or ...) out (either in a narrow beam or isotropically or any way in between), which the bomb on the other train receives, and then blows up?

If I am not mistaken - and I very well could be - the light-travel time between the two tracks/trains is far, far greater than the (remaining) time it would take the lower train to reach its buffer. And when it reaches its buffer, it sends a signal to the bomb on the other train, which means that other train will also explode (while sitting at its buffer).

If so, then we have two explosions, both of which - objectively - take place while the trains at their respective buffers.

 

[Farsight]

Farsight - do you ever intend to answer this question?

All I am asking for is empirical evidence that favours FGR over "MTW" GR. Any progress on that? Because so far, the stuff you have cited has been entirely consistent with "MTW" GR.

Note: this clearly calls for empirical evidence that is inconsistent with "MTW" GR, while being consistent with FGR.

I've already responded to this, and I've already given you the empirical evidence, which Brian has made perfectly clear. The speed of light is not constant, just like Einstein said. And I reiterate, there is no such thing as Farsight GR aka FGR. It's Einstein's GR, or EGR for short. Here's the Einstein quotes again:

1911: If we call the velocity of light at the origin of co-ordinates c_o, then the velocity of light c at a place with the gravitation potential Φ will be given by the relation c = c_oo(1 + Φ/c²).
1912: On the other hand I am of the view that the principle of the constancy of the velocity of light can be maintained only insofar as one restricts oneself to spatio-temporal regions of constant gravitational potential.
1913: I arrived at the result that the velocity of light is not to be regarded as independent of the gravitational potential. Thus the principle of the constancy of the velocity of light is incompatible with the equivalence hypothesis.
1915: the writer of these lines is of the opinion that the theory of relativity is still in need of generalization, in the sense that the principle of the constancy of the velocity of light is to be abandoned.
1916: In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when die Ausbreitungs-geschwindigkeit des Lichtes mit dem Orte variiert.

 

[Farsight]

So if I'm sitting on the event horizon, and I sellotape two torches together so one points up and one points down, and turn both on, what happens to the light from the torch pointing down?

Nothing. It doesn't move. Your torch doesn't shine. To backtrack a little: it takes you an infinite length of time to sellotape your two torches together as measured by observers out in the universe. So you haven't done it yet, and you never ever will.