Minkowski Space Time Briefly Revisited

Minkowski said what he said, and so did Maxwell. See the second paragraph here where he says this: "a motion of translation along an axis cannot produce a rotation about that axis unless it meets with some special mechanism, like that of a screw". Also note the page heading, which is "on The Theory of Molecular Vortices". You have no grounds to dismiss what Minkowski and Maxwell said.

Huff and puff. Depict the electromagnetic field.

I have no hatred of mathematics or competence in mathematics. Instead I challenge your understanding of the physics. I pointed out that in John Jackson’s authoritative textbook Classical Electrodynamics "one should properly speak of the electromagnetic field Fμv rather than E or B separately". So explain it to your grandmother. What's the problem?

It's been me responding to Dan in this thread, in depth, with robust references. You haven't responded to Dan, you've just played the naysayer, and you're making your case with ad-hominems rather than physics.

In your post #14 you refer to a six-dimensional geometrical object called the electromagnetic tensor, but you have no concept of the underlying physical reality. In your post #34 you claim you understand electromagnetism but you still avoid the electromagnetic field, and your reference to monopoles suggest you have not grasped the central issue.

I reject your assertion, my post #36 evaded nothing. My claim about the screw is also backed up by Maxwell. Your alternate explanation isn't an explanation, it's an airy dismissal.

My interpretation is based on rock-solid reference and robust logic. Saying they have opposite charges is a total non-answer, one that evades salient words like spinor and curl and of course "one should properly speak of the electromagnetic field Fμv rather than E or B separately".

I haven't mis-stated anything or confused anything. We surely all know that a charged particle goes around "magnetic field lines".

This says it all. You think the tensor is the reality. It isn't. It's a matrix. An array. The electromagnetic field is a state of space. And it was Einstein who said that, not me. You're lost in maths, rpenner.

I've supported my claim with ample references. You've just played the hubristic naysayer, you've airily dismissed it all, and offered nothing in return. Now it's your turn. You know full well that one should properly speak of the electromagnetic field Fμv rather than E or B separately". You know that the electromagnetic field is a physical field. And that over time, it was realized that the electric and magnetic fields are better thought of as two parts of a greater whole — the electromagnetic field. So draw it.

Dan: sorry about this: I'm afraid the world is full of people who give non-answers, and who are resentful of the people who give answers.

 

Log in or Sign up to hide all adverts.

Farsight, can you show us how to do a GR problem without using spacetime?

 

Log in or Sign up to hide all adverts.

He might have you on ignore. But of course he can because time doesn't exist!

 

Log in or Sign up to hide all adverts.

So, is the answer that, you are that dense or just dishonest?

If you paid any attention, you would know that I have on several occassions said that the idea that space-time is the cause of gravitation (which implies it is something real, as in of substance) is a modern interpretation of GR. I have.., I believe always maintained, that GR and space-time are a description of the dynamic gravitational interaction of objects.., and that the fundamental origin of what we experience as gravitation and best describe with GR and space-time, is yet to be discovered.

So you don't get too confused, I am not saying that GR and the space-time model do not describe something that we should treat as having some substance or pseudo-substance, in its relationship and interaction with the massive objects we can clearly observe, measure and describe... Just that space-time itself should not be thought of in that context.

Now go back and read, note I did not say re-read the GP-B data (not just the dumbed down lay articles and press releases), and try to work out where your mistake is.

HINT the experimental data confirms GR predictions about how a gyroscope (or any object with mass for that matter) would be affected by the gravitational field of a significant mass, in motion.., primarily rotation in this case, but the conclusions can be extended to any motion.

What it does not do is make any direct measurement of space or space-time, though the data obtained is confirmed by predictions made using a space-time model.

The GP-B experiment confirms predicted effects of a rotating gravitational field on a test object, which can be described as a twisting motion of space-time... Your mistake is at least in part assumming that because space-time is described as twisted or twisting, it is something physical rather than just a confirmation that the model space-time is dynamically associated with all motions of any gravitationally significant mass it originates from.

This is all getting a long way from Minkowski space-time introduced in the OP.... More closely associated with the flat space-time of SR.

 

No.

Well you're wrong. Yes a whole pile of people talk about spacetime as if it's the same thing as space, and they blather on about moving through spacetime, but they're wrong.

Huh? Einstein told us all about it. A concentration of energy in the guise of the matter of a star "conditions" the surrounding space, altering its properties, this effect diminishing with distance. As a result the speed of light varies with position, so light curves. Einstein said all this. But there's people out there who say nobody knows how gravity works. It just isn't true. See the OP in this thread. It's really simple.

Einstein described space as a kind of substance in his 1920 Leyden Address. he says things like "to deny the ether is ultimately to assume that empty space has no physical qualities whatever" along with "recognition of the fact that 'empty space' in its physical relation is neither homogeneous nor isotropic".

I haven't made a mistake. The spacetime model works, but a lot of people think space is spacetime when it isn't.

Space is physical. Spacetime is abstract.

The crucial point is that Minkowski* talked about the screw nature of electromagnetism, and you shouldn't dismiss it. Instead you should consider it in the context of what you know about frame-dragging and gravitomagnetism. And gravity, wherein the reality that underlies curved spacetime is inhomogeneous space. But in electromagnetism space isn't inhomogeneous. Instead, as hinted at by Quackhead before he did a runner, it's curved.

* I should add that when Minkowski said "space by itself and time by itself shall sink in the background, and only a certain union of these two shall retain substantiality", he was wrong. He should have united space and motion.

 

Actual textbooks in GR are very explicit about what it means to move through spacetime. They lay out specific mathematical constructions for how this is to be used and how one can describe physical systems.

So far, Farsight-Relativity has no way to describe physical systems. So far, Farsight has explicitly said that his ideas are not to be used to describe physical systems or to do things in physics.

Except that this is a tissue of lies. The lie is that you understand what you are saying, when you do not. The sad fact is that you struggled with mathematics, quit when you had trouble understanding, and then decided to lie your way through the internet.

Einstein developed a theory where the speed of light doesn't vary with position, but where the ways that we describe spacetime leads to definitions of speed that are different from those that we used with an idea of an absolute system of space coordinates and time coordinates. The inference in the theory is from spacetime and the path that light takes to the "speed of light", not the other way around.

And here the lie is that this one public address matters more than any science Einstein produced.

And what doesn't work? Farsight-relativity. It doesn't do anything because Farsight explicitly denies that physics should be used for anything.

And the truth behind the lie here is that Minkowski actually used the mathematics of force-screws in mechanics as an analogy for the mathematics of electromagnetism in special relativity. The sad fact here is that Farsight gave up on mathematics and took up a program of lying to people on the internet.

 

That was an either or question. A choice A or B question.

This side track began when you confused the use of space and space-time in a GP-B article! From everything I see in what you spew, you are confused about exactly what space is and what space-time is.

Farsight, why don't you start referencing something besides public lectures and popular lay oriented articles and press releases? Probably because understanding them is above your pay grade and even if you did understand, it would be far more difficult to twist meaning to fit your predisposed beliefs.

You are one of the confused... Both are abstractions. One abstract because it is a mathematical model describing the dynamics of gravitation.., and the other abstract because it is a word that describes an idea, better understood as everything other than the matter and perhaps energy we can directly measure and observe.

Off on another unrelated tangent... The OP specifically mentioned Minkowski in the context of Minkowski Spacetime.., which doesn't have anything to do with curvature or screws... It is a flat space-time mathematical model that was intended to better explain the flat space-time of SR.

This whole side track, has nothing to do with the intent of the OP the way I read it. I think if someone started a thread about the 2D geometry of a piece of paper, you would find some way to make even that a discussion of Eimstein's Leyden address and a variable speed of light!

 

As always you're sharing some very informative 'stuff'. My first experience with 'gravitomagnetism' was deriving it from the Kerr metric. My path is backassward since I didn't study any physics until I was 50 years old. I appreciate you sharing 'stuff' with me.

 

I am thoroughly confused by your posts. First you say

Leaving aside that a tensor is NOT a matrix - it's a multilinear mapping from a tensor product of vectors onto to reals (though its scalar components are conveniently represented as a matrix, this is not essential(.

Jackson here seems to be referring to the scalar components of a tensor field i.e a single tensor applied to each and every point in spacetime (there's more to than that, but leave it for now)'

So unless you are asserting that a) the tensor field enjoys the same status of "reality" as the EM field , or

b) the EM field enjoys the same same status of "physical unreality" as the tensor field

then you seem to making contradictory assertions

PS by edit Of course Jackson might mean that the field strength tensor defined at a certain point "takes the place of" the EM field defined at the same point. In fact I rather suspect he does, but this in no way removes your own contradiction

 

I really liked the brief diversion here into gravitomagnetic force, which wasn't discussed in any detail in the previous Minkowski threads.

rpenner gets gold stars for the best explanation of gravitomagnetism so far, and all of us here know he has math to back it up.

I like to think of gravitomagnetism as another on a long (and getting longer) list of perturbations to gravitation based on GR theory. Start with rubber sheets with grids like Farsight drew. Add one gravitating body and you get a dimple that moves along with the approximate center of that body. Add another, somewhat smaller gravitating body orbiting the first, and you get a contribution that shifts the center of the dimple and alters its shape as the second body orbits the first one (and vice-versa). Add a third body to the picture that closely approaches and then slingshots away from the first two. The perturbation will NOT ONLY depend on the mass of the third body, but also on the non-negligible amount of kinetic energy that is bound in its relative motion with respect to the first two, as if all of them were more massive than they would be if they were at rest or moving more slowly. This is gravitomagnetism as I understand it. "Analogous" to electromagnetism, as rpenner said. You get more gravity by increasing rates of relative motion, the same way you get more current output capacity, up to a point, from a generator by increasing rpm.

Add things like the anomalous acceleration of deep space vessels equipped with outboard nuclear reactors, and other effects like uneven mass concentrations, solar wind, and then you quickly get a situation which means you need sophisticated sensors, an extra supply of hydrazine and a steady hand at the remote telemetry controls in order to soft land on a comet. It isn't all fixed in math at the beginning of a space launch. Sometimes you even get it so wrong that expensive gear like the Mars polar orbiter crashes because Lockheed performed calculations using miles instead of kilometers, right after they took over Comsat, where I was working at the time. Something of an embarrassment for an associate of a company built on Arthur C. Clarke's vision that previously had earned a sterling reputation in satellite and celestial mechanics perturbation calculations.

I will resist moving further into the many omissions of this view of gravity for the purposes of this thread (which always gets me into trouble here anyway). I've learned a lot, and have beaten my Higgs obsession, I think, for now.

So, how is it that objects constructed of matter or bound energy appear to undergo both relative length contraction and time dilation effects at relativistic speeds, yet unbound energy such as light only have Doppler shifts? A pulse of light that appears 1 meter long in the rest frame, like the one "cheated" in that video at the beginning of this thread, stays 1 meter in the rest frame for as long as it travels, right?

If you move (fast!) in a direction that is opposite the direction of propagation of that 1 meter long pulse, the pulse blue shifts and contracts as it is approaching you, then red shifts, (but does not expand) as it gets further away? Is this the right picture, according to Lorentz and Minkowski?

Note: I'm cheating a little because a laser pulse is already a form of bound energy, no matter which direction it propagates, but you could do the same analysis with a point (spherical wave front) light source.

What if I wanted to move in a manner so that that light pulse Lorentz contracted to zero length? Is that even possible?

 

IMHO a better way of envisaging gravity is to start with a gin-clear block of ghostly elastic jelly, with lattice lines drawn in it so you can see what you're doing. Then you slip in a hypodermic needle and inject more jelly in the middle. This creates a pressure gradient pushing out the surrounding jelly. When you "zoom in" to avoid being distracted by the rotational symmetry of your planet, what you see is something like this:

Please Register or Log in to view the hidden image!

It's something like you skew the above depiction for gravitomagnetism. But note that it's extremely weak, much weaker than gravity, which is much weaker than electromagnetism.

Interesting stuff Dan. Yes there's various components to the stress-energy-momentum tensor. I think the shear stress is an eye-opener, but it never seems to get any attention.

Please Register or Log in to view the hidden image!

Oooh, Higgs. Start a thread!

Good question. People say objects get length-contracted, but they never point out that light waves don't. I think length contraction deserves a whole new thread actually.

That pulse doesn't change a bit.

No. length contraction doesn't work the way people think. Think about the situation where you and I are moving past each other fast. Let's say we each have adopted a "Superman" pose, effectively lying down with our arms outstretched in front of us. Let's also say that we're each 2 metres long. Let's also say that we're each carrying a 1-metre butterfly net. We can't scoop each other up. Check out the pole and barn paradox.

 

You'll forgive me if I avoid hijacking Dan's thread with any more arguments. But take a look at Einstein talking about field theory in 1929:

"Expanding the Theory
This theory having brought together the metric and gravitation would have been completely satisfactory of the world had only gravitational fields and no electro-magnetic fields. Not it is true that the latter can be included within the general theory of relativity by taking over and appropriately modifying Maxwell's equations of the electro-magnetic field, but they do not then appear like the gravitational fields as structural properties of the space - time continuum, but as logically independent constructions. The two types of field are causally linked in this theory, but still not fused to an identity. It can, however, scarcely be imagined that empty space has conditions or states of two essentially different kinds, and it is natural to suspect that this only appears to be so because the structure of the physical continuum is not completely described by the Riemannian metric."

According to Einstein, a field is a state of space. In simple terms, I'd say you should think of a gravitational field as a place where space is "pushed outwards", and think of an electromagnetic field as a place where space is also "twisted around". I think the important think to appreciate here is that the space where the electron is doesn't have two different states.

 

And what affect do you think the last part of the sentence you emphasized has on its meaning? (Indicated by my change in emphasis above.)

It does not sound to me, that when Einstein used the term empty space, he meant the same thing you believe he did.., because he completed his thought with the comment, the structure of the physical continuum is not completely described... where it apears the physical continuum modifies the earlier reference to empty space.

The idea of space and empty space has never been completely described or better defined. In Newton's context it is easy to assume that empty means empty. That is no longer the case in GR and yet the structure or composition of what is called empty space is not defined. The substance of a field, without some clear definition, is essentially virtual. GR describes how mass and empty space interact within the context of gravitation, but he and no one since, has provided a convincing definition/description, or as Einstein put it, the structure of the physical continum is not completely described. So we can describe the interaction we call gravitation without clearly describing one of the interacting parts, empty space. That is, in at least part, what is being attempted by those working on models of quantum gravity... And what leads many on lay forms like this to speculate about the resurrection of the ether in one context or another.

 

Your pedantic nonsense knows no bounds.....space, time, henceforth known as spacetime, are actually the same thing.

"The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality". – Hermann Minkowski, 1908


I'm not real sure what NASA article you are referring to, but knowing your record for misinterpretations, out of context quotes and just plain old porky pies, I would suggest that the article confirms what I have just said.

 

Here is the link I should have provided at the beginning, with Ramesh's original TED talk example of a moving laser pulse measuring stick we are now using:



Sorry for the delay. It took me a while to find the femto camera video.

 

It was cited several pages back... But was an old lay article describing the GP-B experimental conclusion confirming frame-dragging. It used twist/twisting as a description 13 times with the word space-time and once with the word space. Which was followed in the next sentence by the space-time use again. Farsight took hold of the single typo using the word space.., and as usual...

 

I'm not confused about space and spacetime.

You need to read his 1920 Leyden Address where Einstein said "the recognition of the fact that 'empty space' in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gmn), has, I think, finally disposed of the view that space is physically empty." The important thing is that space isn't nothing. It sustains waves and fields. See the shear stress in the stress-energy-momentum tensor, it's like space is this gin-clear ghostly elastic stuff that waves and curves.

It is a kind of resurrection of the ether. Einstein's Leyden Address is where he says this: "Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether." Also see this:

"Robert B Laughlin, Nobel Laureate in Physics, endowed chair in physics, Stanford University, had this to say about ether in contemporary theoretical physics:
It is ironic that Einstein's most creative work, the general theory of relativity, should boil down to conceptualizing space as a medium when his original premise [in special relativity] was that no such medium existed [..] The word 'ether' has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum.".

And see arXiv for papers with aether in the title.

 

I agree. It is unfair to say that you are confused about concepts that you are almost completely ignorant of. You cannot use either to do physics, so you can't possibly confuse them.

And you need to read a textbook on physics and learn how to do it. You have admitted that you cant do any physics with your fantasies.

It is insulting that you say all this without bother to learn what Einstein actually did.

 

I'm the one referring to Einstein and the evidence and the various papers here. Not you.

Please Register or Log in to view the hidden image!

 

I was trying to pull a fast one based on the femtosecond pulse in the last example I gave, and no one called me on it.

If you are watching a pulse of light pass by your position, and with no scattering as shown in the video, of course after it passes you see nothing, because the light pulse isn't traveling in your direction any more.

One of the stills from the video comes out looking redder on the right side of the coke bottle and bluer on the trailing left edge, but I'm pretty sure that effect isn't from Doppler.

People have tried to use Doppler shifts as a way of questioning things like the twin paradox, but they are unrelated.

Thanks for all who responded in great detail. I did wish to keep this revisit into some things discussed in connection with Minkowski space-time brief, and we did cover a few points that were missed before.

I'm convinced that light or energy pulses Lorentz contract in the same manner that matter does. This makes perfect sense. The natural state for matter is to be "at rest". A universe with enough concentrated matter in one spot is about as "at rest" (and also as compact) as it gets. The natural state for energy is in motion, but without the concept of "space", where would it all go? Six of one, half dozen of the other.

Partly because of this, I'm with Farsight on one critical point. 'Spacetime' really does not exist, because the spatial component we attribute to it does not actually exist. This is why "space" seems to contract or expand to basically any dimension you might like it to be, and the energy content of either energy or matter is undefined may likewise be anything you want it to be, because it changes with relative motion. It is an artifact of the motions of matter and/or energy through a dimension which seems to have properties of time, combined with changes in direction "twistiness", for lack of a better term for it. The limited speed of light for both matter and energy is the only thing that makes such a universe possible. "Twisttime"? Chubby Checker would have approved.