Tim88

41 minutes ago, beecee said:

The various effects of gravitational time dilation with regards to objects/matter/energy approaching an EH, in any frame of reference do nothing to invalidate the overwhelming evidence to support the "Gravitationally Completely Collapsed Object" as defined by GR, or if you like the BH. The evidence supporting them is verifiable. 

That's more to the point. Do you mean that simulations that have particles forever more slowly falling towards the centre, using GR equations from our point of view, do not agree with observations?

On second thought, likely you just mean that there is overwhelming support for the gravitational collapse of stars, which is getting back to the topic of this thread.

35 minutes ago, Strange said:

It never slowed down, so it will continue to increase in speed after it passes the event horizon.

Form the external observers frame of reference, it ceases to be visible before it reaches the event horizon so the "frozen" thing is moot anyway.

"It never slowed down"??. Correct is to say that -of course- from its own frame of measurements, it never slows down.

From our frame of reference not only those objects become invisible, anything that would be observed by co-moving observers is unverifiable - moot as you say.

On 4/18/2019 at 7:05 PM, michel123456 said:

"even in relativity there can only be one single reality" - Happy to read that from someone like you.

"From someone like me"? It's a corner stone of doing science....

On 4/18/2019 at 7:05 PM, michel123456 said:

["The in-faller 'really stops cold' at EH as directly measured by string motion at external observer"] If that is true, then for the external observer the BH is void, all its mass lies on its surface at the EH.

Just now I got an email from Qreeus telling me that he found a mistake in that analysis. Indeed, that could hardly have been correct, as it seems obvious that in that region anything has to keep moving at locally c.

On 4/18/2019 at 7:39 PM, Strange said:

[..] For one thing, there is no surface and so nothing to stop material falling in. And for another, the event horizon grows to encompass matter falling in so it wouldn't even appear to be "frozen" at the surface.

There is indeed no literal surface; instead, as interpreted by a distant observer, there is the huge gravitational potential that slows down in-falling objects so much that their radial speed becomes nearly zero.

Further, a growing event horizon will of course displace that "surface" to beyond that position - kind of "burying" the particle inside the zone of extremely high gravitational potential. If I'm not mistaken, the gravitational potential won't be reduced below that "surface"; consequently, such burying cannot make it speed up again.

Just now, swansont said:

Q-reeus

You need to use the correct username in your search, and as you’ve been a member for almost 3 years, you’ve known about this forum for a while

I meant that he reminded me of it. And oops you are right - thanks! OK that works

On 4/16/2019 at 9:18 AM, Q-reeus said:

[..] it's no 'optical illusion' that the in-faller freezes at the EH - as seen from outside. The logical consequence of having coordinate c -> 0 at 'EH' is that from in-faller's 'stopped coordinate-time clock' pov the entire rest of universe is infinitely old at the moment he/she hits the 'EH'.

Indeed. Although, I find "of having coordinate c -> 0 at 'EH" is that'" somewhat poorly phrased, I would say "of having c -> 0 at the 'EH' position" ; and it's a bit ambiguous that he referred to the pov of the outside observer, according to whom there would indeed be an "in-faller's 'stopped coordinate-time clock'" at that position.

Anyway, it makes much logical sense, even in relativity there can only be one single reality! He could be more polite though (not that he's the only one here...).

Note: yesterday Q-reuss mentioned this forum to me and just now I tried to search his contributions in other threads - but regretfully that became impossible! Apparently that is related to the fact that a few hours ago he was "permanently banned for spamming the forum with nonsense".

Well then, ... Good luck.

On 21/08/2017 at 1:26 PM, swansont said:

Doubtful
https://en.wikipedia.org/wiki/Earth_orientation_parameters
http://hpiers.obspm.fr/eop-pc/earthor/EOP.html

Why would they mention a precession-nutation model if they didn't include nutation in it?

[..]

No, not those; that's not what is meant with "the predecessors". The comparison is with the simplified calculations for time periods of 100'000 yrs and more, the so-called Milankovitch calculations and variants thereof - http://www.indiana.edu/~geol105/images/gaia_chapter_4/milankovitch.htm .

On 17/08/2017 at 0:04 PM, swansont said:

I don't understand your comment. The 18.6 year nutation period was already known and used in earth orientation models. It's not being ignored.

This web page is from 2009
http://maia.usno.navy.mil/whatiseop.html

"Periodic variations are associated with periodically repeatable physical processes affecting the Earth. Tides raised in the solid Earth by the Moon and the Sun produce variations in the length of the day with a total amplitude on the order of 0.001 seconds and with individual periods of 18.6 years, 1 year, 1/2 year, 27.55 days, 13.66 days and others."

I get the impression that the models lag the measurements. That there's a model that predicts the observed nutation changes nothing for the people who were already using the accurate measurements in their work. What exactly were you expecting?

Apparently the approximate calculations that everyone used until now do not even include the nutation; in other words, those do not "lag" the measurements but simply don't reproduce them - and apparently they were wrong for their intended use as well. The correct and accurately calculated nutation is one of the verifications of the correctness of the new, exact calculations that are discussed in the paper. Regretfully, we cannot directly verify the calculations over 100'000s of years with measurements.

I now got a reply from Smulsky.

He points out that in fact there is an additional, astronomical verification: the constant of nutation. That's an oscillation of 9.2'' with a period of 18.6 years - https://en.wikipedia.org/wiki/Astronomical_nutation#Nutation_of_the_Earth.27s_axis

As described in Smulsky's fig.10, this observed phenomenon is exactly reproduced by his calculation model  -  Smulsky J.J. Fundamental Principles and Results of a New Astronomic Theory of Climate Change. 

He further comments in his email (with a slight correction of his Google Translate Russian->English), with added emphasis:

Quote

In addition, the previous solutions of the problem of the Earth’s rotation are incorrect in the interval 0-2000 thousand years, since they do not give short-period oscillations of the Earth's axis. New solutions give them (see Fig. 10).

It looks to me that there is no reason to doubt the new calculation results. Thus, the one year silence after his peer reviewed publication suggests to me that people are putting their heads in the sand, in an attempt to just ignore it.

21 hours ago, swansont said:

No, but in an assertion of something without any constraints, i.e. something that's offered as being generally true; all you need is a counter-example to show it to be false. A rigid body in free space cannot undergo a constant rotational acceleration without an energy input. Angular momentum and energy are conserved. Is that sufficient clarification? (I would have thought this to be obvious, and uninteresting)

Probably you misunderstood him. He was comparing constant straight line acceleration with constant centripetal acceleration (= in a circle, or "rotational"):

Quote

Travelling in a circle is a different kind of acceleration though. It's not continuous, but constantly changing in direction.

In contrast to rectilinear acceleration, there is no energy input.for the simple case of a body that is freely rotating at constant centripetal acceleration (constant rotation speed).

On 11/08/2017 at 8:30 PM, mistermack said:

No external source of energy is needed for a constant rotational acceleration. It could continue for ever without any input. 

On 12/08/2017 at 2:14 AM, swansont said:

No, not true for a rigid body.

mistermack didn't say "rigid body"... anyway, that's an interesting assertion; please clarify!

On 16/05/2017 at 2:52 PM, TakenItSeriously said:

• Were their any unexpected anomalies found in Bells Inequality test data aside from those predicted by QM?

On 10/08/2017 at 1:19 PM, Tim88 said:

[..]

More on topic, I recall that I read somewhere that the results of some well known Bell type measurements do not agree well with the predictions of QM, but that this fact was overlooked in the first article on those experiments (sometimes one only sees what one is looking for). I will try to find that back.

I now found it back: https://arxiv.org/abs/1112.2629

In a nutshell, the authors conclude that the experimental data by Weihs et al are not in agreement with the predictions of QM:

"It is highly unlikely that quantum theory describes the data of the EPRB experiment that we have analyzed."

As it's apparently only in ARXIV, it's definitely a discussion item - up to TakenItSeriously if he's interested!

As I now understand it, the approximate and the accurate calculations are all accurate (agreeing with each other and with measurements) for the time of human history.
Consequently, it is necessary to compare the calculated variations with the geological record. In the paper a comparison is made with the ice ages, as established with dating techniques.

19 hours ago, mistermack said:

Thanks, I get what you are saying there. 

One question that occurs to me though, is can an accelerating frame of reference be real? I can see how it works locally and temporarily, but as far as the Universe goes, it would mean that the total energy of the Universe is constantly rising.

So I can picture an accelerating reference frame, no problem. But can one exist, other than as a local effect?

If you take it to it's logical conclusion, an accelerating reference frame would have everything in the Universe moving faster than light eventually. Or, on the elevator, a constant acceleration of 1g would take you past the speed of light. 

Indeed accelerating frames are for local use; that was already done in classical mechanics but GR extended it for all physical phenomena.

There's another issue that none of us addressed but is coming back every time: there is no "moving faster than light eventually" involved. Accelerating objects as measured with a "stationary frame" (also called "coordinate acceleration") accelerate less and less fast as they reach high speed. That was even one of the first predictions of SR, about the fact that electrons cannot be accelerated to the speed of light.

Note also the subtle difference with proper acceleration, which is the acceleration relative to instantly co-moving reference frames.The fact that nothing can break the speed of light is true for someone who has a constant proper acceleration of 9.8 m/s².

Hi Mordred, thanks for the wealth of references.

I doubt that Bayesian vs Gaussian statistics matters here, as I cited how Bell did not even pretend to give a rigorous proof of his starting equation. Nevertheless, since I have the statistics book of Jaynes [PS I'm well beyond chapter one lol] and still plan to work my way completely through it one day, your references are appreciated and maybe one day I'll contact you with questions about a certain chapter.

Also, I agree that the "particle" approach is probably a dead end - just for the record, as we're drifting away from the topic (sorry TakenItSeriously!).

More on topic, I recall that I read somewhere that the results of some well known Bell type measurements do not agree well with the predictions of QM, but that this fact was overlooked in the first article on those experiments (sometimes one only sees what one is looking for). I will try to find that back.

On 02/08/2017 at 8:41 PM, Mordred said:

here is a prime example.

p(ab|xy)=∫adλq(λ)p(a|x,λ)p(b|y,λ)p(ab|xy)=∫adλq(λ)p(a|x,λ)p(b|y,λ)

this expression is what defines locality in Bells experiment.

That's a good one! In fact there seems to be something of a mathematical "anomaly" here. That equation is according to Jaynes an unproven simplification of locality in Bell experiments. According to him, "fundamentally correct" would be (in his notation):

P(AB|abλ) = P(A|Babλ) P(B|abλ)

Now, I'm not 100% sure that he was right, but I suppose that an expert like him would not make a mistake about such a fundamental issue. And as a matter of fact, even Bell admitted that his simple equation is not based on mathematical rigor but instead, it is based on plausible looking assumptions ("It seems reasonable to expect that" - Bertlmann's socks).

As the result led to extraordinary claims, extraordinary evidence is required. Reasonable seeming expectation does not suffice.

38 minutes ago, studiot said:

If more than one definition / interpretation is available, then it is incumbent upon a writer to make it plain which one is in use at any point in the writing.

Otherwise it can easily lead to one definition being set against another, as I noted.

What does that obvious fact have to do with the issues that PrimalMinister and mistermack have with interpretations of relativity by certain writers?
As I understand their issues, they are struggling with a mix-up that happens at the source of information. The issue here, I think, is not that writers are unclear or confusing about their definitions. All too often -even in textbooks- metaphysics is sold as physics, sometimes even accompanied by misleading or false information. That causes the most confusion.
Let's wait for their comments.

16 hours ago, mistermack said:

That's fine, except that I keep reading that gravity isn't a force. [..]

But it's not acceleration either, because I'm not gaining kinetic energy. 

How about this: Einstein speculated in 1916 that "The general theory of relativity renders it likely that the electrical masses of an electron are held together by gravitational forces." (in Relativity: The Special and General theory, English translation of 1920).
- https://en.wikisource.org/wiki/Relativity:_The_Special_and_General_Theory/Part_I#cite_note-14

Once more (sticking to the topic), it's all a matter of interpretation and definitions, quite independent of the mathematical theory.
 

14 hours ago, studiot said:

 

In Newtonian mechanics, which is all we need here, gravity is most definitely a force.

The interpretation of gravity as some sort of warping of spacetime (not space) is non Newtonian.

You should not mix Newtonian and non Newtonian physics.

Adding to that, it depends on one's definition of "force"  if we call it a force or not. In fact, Einstein still called it a force in 1916 when he explained GR. Plays on words should not hinder our understanding!

What exactly do you understand with "absolute time", and why do you think that it has been shown not to exist? Negatives are generally hard to show!

Note the subtle difference with the fact that time is not absolute. Maybe that is what you meant?

On 02/08/2017 at 1:12 PM, PrimalMinister said:

I know relativity has been 'proved' but how do you know its what is actually going on as opposed to something that works but is not true/real such as epicycles. How do we know this is not just a repeat of this, making theories that work but are not true/real. Relativity seems like this to me, it is obviously onto something but I don't think its the actual truth, i.e. I don't think space-time literally bends and warps, I think the equations work (in certain conditions) but are not describing actual reality.

"Bending and  warping space-time" is in fact a geometrical description of the mathematics. You definitely don't have to that literal, as a description of "hidden reality".
Here, just do a word search in one of the most famous papers, and see if you can find "bending and warping space-time", or something equivalent :

http://fourmilab.ch/etexts/einstein/specrel/www/

Special and General relativity are in fact mathematical models that make, for the time being, rather satisfying predictions about natural phenomena; they do not pretend to tell us "what really happens". However they do  strongly limit the options of what may be "really going on", or "under the hood" so to say. I have no idea if your "cellular automata" are compatible. But that brings us out of the realm of physics in the narrow sense of the word. Happily we have an appropriate sub forum for that. For a discussion of two historical interpretations that work, see http://www.scienceforums.net/topic/98845-models-for-making-sense-of-relativity-physical-space-vs-physical-spacetime/

1 hour ago, swansont said:

[..] that was not the only statement of bvr's which I objected to. The clock analysis — that the timing changes because of the distance between atoms (which allegedly increases?) — is bogus. The simplest rebuttal is that you can have a clock that's a single atom or ion. Or a linear ion trap, situated in the vertical direction. There is no length contraction effect, and yet the time will follow relativity.

From my side I also have some difficulties with posts by different people, for example I can guess what bvr may have meant with "measuring light with light", but I'm not sure. Probably it's an oversimplification; remember the intended level of this thread. I hope that he'll clarify that as geordief already asked for.

Concerning time dilation, the simplest illustration is the light clock - which is a very nice illustration of time dilation at a beginners level and appropriate for this discussion. It illustrates something similar as what bvr may have had in mind (again simplifying). As determined in the "rest" frame, the light clock's "time" is indeed "dilated" because the signal trajectories between "moving" atoms (mirrors in this case) are increased. That's the first stepping stone towards understanding the Michelson-Morley experiment. It may be useful for geordief to have a look at it.
- https://simple.wikipedia.org/wiki/Light_clock
- https://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_velocity_time_dilation
(not sure that "simple wikipedia" is the easiest to understand)

On 05/08/2017 at 2:15 PM, swansont said:

Yes, I am talking, in this particular case, about an external EM field. What Tim88 posted assumes such a field. length contraction is not related to this.

That's probably the same misunderstanding: what I quoted from Bell was about length contraction (the Lorentz-Fitzgerald kind) related to internal EM fields. That's part of a more "constructive" approach to teaching SR.
PS: that is exactly what bvr meant with the remark that you claimed to be wrong, as we see just now in his latest post.

If you think that you can disprove Bell's "How to teach relativity" then please start it as a new topic, so as not to hijack the discussion here about understanding light propagation in SR. It would certainly deserve a discussion thread on its own, and it can be interesting.

4 hours ago, swansont said:

"The structure of an object results from the balance between forces in all directions. When the object moves, a new balance gets settled between the transverse and longitudinal forces, what results in a contraction in the direction of the movement."

No. There is no "new balance" (or equilibrium) of these forces. It's exactly as if the object wasn't moving (which, in its own frame, it isn't). The two conditions, being inertial motion, are identical with regard to any internal or external forces.  

Huh? "in its own frame" the object is of course not moving; that's besides the point. Similarly, a fast moving object has increased kinetic energy compared to rest; the objection that this is wrong because "in its own frame" this is not so, is irrelevant. Maybe I overlook some big error but more likely you misunderstand what bvr is saying here. Bell explained in his famous "How to teach relativity" the implications of the Maxwell equations as follows:

"The magnetic field is transverse to the direction of motion and, roughly speaking, the system of lines of electric field is flattened in the direction of motion (Fig. 4). In so far as microscopic electrical forces are important in the structure of matter, this systematic distortion of the field of fast particles will alter the internal equilibrium of fast moving material. It is to be expected therefore that a body set in rapid motion will change shape."

On 03/08/2017 at 11:41 AM, swansont said:

How did these calculations match up with predictions (or did they do such a comparison)? I have colleagues who measure the orientation of the earth's axis. There are also models, which as I understand it are fairly complex. There are a number of different oscillation cycles present, as well as effects of redistributing mass on the earth.

You can see here that the pole wanders by a few tenths of an arc-second over the course of a year, and is cyclical
http://www.usno.navy.mil/USNO/earth-orientation/eo-info/faq/what-is-pm

As I understand it, they only compared different accurate calculations with each other and with the old ones, which most others still use. Apart of that, they obtained a better match with the historical ice ages - but that is of course very indirect. Thus I like your reference to direct measurements -thanks! I may write to the author and ask if they considered comparing with such direct measurements.
However it may be that the time frame is much too short. And I do not quite understand that picture: "a reference frame which is defined by the adopted locations of terrestrial observatories. The coordinate x is measured along the 0^o (Greenwich) meridian [..]". I thought that the North Pole defines that reference frame - in which case it cannot move relative to it, right??

3 minutes ago, geordief said:

Pardon my ignorance (genuinely) but  in a non-em wave scenario  (say sound waves) does the wave also propagate at a speed that is independent of the velocity of the emitting  body?

 

Suppose a bullet pierces a  metal plate, would the sound produced be heard  by an observer "upstream" later than an equivalent observer "downstream" (in the direction of motion of the traveling bullet) -or would both hear the sound waves at the same time. (I do know that the sound would be higher pitched to  the latter observer but would both receive the traveling sound wavefront simultaneously?))

If they are at the same distance and with the usual assumptions (the lab and the air in rest, etc) then they should also hear the sound at the same time.
Compare https://en.wikipedia.org/wiki/Wave#Acoustic_waves