## Posts Tagged ‘General Relativity’

### FTL: Faster Than Light Communications Don’t Violate Causality

April 30, 2020

Many physicists take for granted that if Faster Than Light (FTL) communications were possible some signals could be received earlier than they have been emitted. That’s not correct. “Proofs” that Faster Than Light would demolish causality rest on a confusion between causality and temporality. Time is affected by motion, causality isn’t.

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LIGHT/GRAVITY OBSERVED SIMULTANEOUSNESS OF EVENTS IS SPEED DEPENDENT:

Let’s call the Fast Frame FF and the Inertial Frame IF. The great result of Poincaré is that if a clock in Inertial Frame is accelerated to Fast Frame, once it sits still in FF, it will run slow (it’s called the “Twin Paradox”).

Henri Poincaré pointed out as early as 1898 (Einstein was 19), events which are VIEWED AS simultaneous in the Fast Frame FF may not be VIEWED AS so in the Inertial Frame IF  depending on the exact motion of FF. (If light behaved as sound, it would be obvious why: sometimes sound takes longer to catch up. It’s basically the same mathematical idea.)

The fact events look simultaneous, or not, depends upon defining simultaneity with light speed, and that c is finite. The sketch above is ROUGHLY correct… But not really, because it contains implicitly a subtlety which needs to come to the fore to be fully correct: the LOCAL time inside the train is NOT the same as the LOCAL time on the platform watching the train… so the detail of the drawing is not as simple as the first sketch… But the basic concept remains: light will be seen as hitting the left side of the carriage first if the carriage is moving towards the right…

It’s very simple. Let’s visualize IF and FF the former as a train station, the second as a train, rushing by. Consider the two extremities of a carriage, A and B, call M the middle of the carriage. Then shine a light at M. From inside the carriage, one can see (say by reflecting the light on mirrors), that the light arrived at A and B simultaneously.

However, from the outside, as seen from the Inertial Frame, the train station, as the carriage is going towards M, the light is going to hit A first, and B, later.

The proof rests only on the speed of light being finite (something we have known since studying the moons of Jupiter in the Seventeenth Century.

So simultaneousness of events having to do with light as defined in the Inertial Frame will be different from simultaneousness of events having to do with light in the Fast Frame… As seen with light!  The order of some events may appear one way in IF, and the opposite in FF. If one defines causality as temporal ordering, one is lost. All of this was discovered by Henri Poincaré… and probably why Henri proposed to call this “the theory of relativity”… Relativity of light events as seen by light. All very enlightening, but all too light.

Now here is a philosophical question: suppose we have an instantaneous way to communicate when things are happening. Would that redefine simultaneity? Of course. now in the real world, spacetime is curved, and light goes neither straight, nor constantly, and may even not go anywhere at all:

Spacetime is curved, and in other words, light is neither straight nor constant. More precisely this means that parallel transport along a ray of light brings a rotation of frames. Also shrinkage in various dimensions.

At first sight, physics locked the notion of time down. Indeed, at first sight…. we have only two long range interactions: gravity and electromagnetism (light). Moreover because of Energy = Mass (Henri Poincaré, 1899, La Sorbonne, Paris), they go at the same speed.

At second sight, we have Quantum Entanglement… Yes, I know, many physicists say Quantum Entanglement can’t be an interaction, because it would go faster than light, and that would violate causality. They may as well quote the Bible… It’s faith on their part, and dogma, not science…

Moreover, time, as defined by light clocks is only local, a notion living in the tangent space to spacetime. An explicit illustration of that is local time in a GPS satellite is not Earth time, and modifications to clocks have to be made constantly.

In this real world, defining time only with light is not the only problem. Wait, some will say, do you have any better than light and gravitation to tell us of distant events? Of course, we do: Quantum Entanglement. In my vision of the matter, matter, and space are literally created by Quantum Entanglement. And that goes at a faster clip than electromagnetism and gravity, or things would fall apart.

Patrice Ayme

### Gravitational Waves Directly Detected

February 11, 2016

How Were Gravitational Waves detected?

By two detectors in the USA, one in Washington State, the other in Louisiana (detecting in one place would have been enough; in two places at the same time, the finding is overwhelming certain; the National Science Foundation of the USA had spent \$1.1 billion, over 40 years, on that research). The detectors were simplicity themselves in concept: just a light interferometer to measure the distance between mirrors: light is split, sent in two perpendicular directions, and then re-united with itself. If one of the branches vary slightly in length relative to the other as a gravitational waves passes, an interference will show up. However mirrors hanging from pendulum hanging from pendulums five times, the whole thing in an anti-vibration machine had to be realized in half a dozen places in a chain of reflections and interference.

What are these Gravitational Waves?

As far as existing gravitation theory has it, distortion in space (and, thus time: time and space are related by the speed of light, c).

A Field Carries Away A Wave Just As A Whip Does

What Was Detected:

Einstein’s Gravitation Theory says that gravitation “is” the deformation of space(time) it brings. It is this deformation which was directly detected: a part of space in one direction was made shorter than in another direction. That meant a huge gravitational wave had passed.

The formidable event that caused it was the crash and collapse of two black holes into each other, each around 30 solar masses (much more details are known).

Gravitational Waves Were Certain Theoretically, & Already Detected:

We already had evidence for the existence of gravitational waves, both theoretical and experimental. Einstein’s name was rolled out, naturally enough. Because Einstein contributed to the present Theory of Gravitation (I am not anti-Einstein, far from it, but he closely worked with a number of other people, including the towering mathematician David Hilbert, who published his own approach to gravity within weeks of Einstein).

Einstein tends to appear as the cherry on many a cake. Those who celebrate the photogenic cherry, and ignore the cake, will go hungry.

WAVES ARE PREDICTED BY FINITE SPEED FIELD THEORY:

Actually, once one has hypothesized that gravitation is a field propagating at a finite speed, the apparition of waves is automatic.

The reasoning was made first by British and French Eighteenth Century physicists, in the framework of electromagnetic force; the mathematics is exactly the same with gravitation, as both fields vary with the inverse square of the distance. This is what happens in a radio antenna, with electrons going back and forth: the electric field that those electrons create is deformed in such a way that it moves other electron at a distance, back and forth.

The Gravitational Energy Loss Detection Method:

Thus, how do the waves show up? By shaking things at a distance. Using conservation of energy, it means that the field creating system, by moving just so, loses energy to its waves. An obvious case is two neutron stars (“pulsars”) rotating around each other: as they move back and forth, because of said rotation, they create gravitational waves which carry energy away from their system, As this happens, their system loses energy, the two stars should spiral into each other, thus rotate ever faster, and this should be observable, and computable exactly. This, indeed, was thoroughly observed, so we knew the waves were there.

Einstein’s Gravitation Theory is a sleight of hand:

It affects to identify space(time) deformations with gravitation. The idea actually originated with the awesome German mathematician Bernard Riemann, who invented manifold theory in part to point out that any force could be viewed as convergence, or divergence of geodesics (this is an idea that physics has been milking ever since).

This, though, does not answer Newton’s deeper query about the nature of gravitation (see below). It’s a bit as if a creature asked:’What is an arm?’ And one answered:’An arm is what pushes things, and we can detect the deformation the arm brought.’

What is the discovery good for?

Well, first, one has to make sure. Science is about making 100% sure. The present experiment improved some technology far out what anything else required (but then it does open some possibilities!) Just an importantly, now we will be able to check the details of the Gravitation Theory (the big picture was not in doubt; the details are). Ultimately it may be possible to communicate through gravitational waves, etc (although right now the deformation are only of the size of the fraction of a nucleus, and we could detect them!)

Who were the originators of that idea? First Newton himself pointed out that his own theory of gravitation was grotesque (I am paraphrasing). Newton:

“that one body may act upon another at a distance thro’ a Vacuum, without the Mediation of any thing else, by and through which their Action and Force may be conveyed from one to another, is to me so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it.”

There were actually two problems: that the action was instantaneous, and that it was at a distance without intermediaries. Newton paid attention to the second one, physics, in the last two centuries, solved the first (which was implicit in Newton’s observations).

As I mentioned in passing above, part of Newton’s worries were addressed by the invention of the concept of field. And then by the realization that fields carried energy away in waves. At that point, gravitational waves were automatic… Riemann’s introduction of manifolds, and how to conceptualize forces in them gave the manifestation of its nature to gravitation we presently have, a distortion of space metric (once again, time follows automatically).

It’s important to know who invented what, and contributed most. Because it unveils how ideas appear and evolve. Then, in turn, one can make theories of that, accelerating innovation (don’t forget there is a horse race between innovation and oblivion, on the scale of the entire biosphere!)

Curiously, this is all very useful; GPS with a precision of 30 centimeters has allowed to find out that baboon society is more democratic than ours, in fundamental ways. “General Relativistic” effects (the fact clocks run slow in a gravitational field) make crucial corrections to the GPS computations (otherwise GPS would be pretty useless). So this is not all academic. GPS will soon allow robotic agriculture… among other things.

We still don’t know what gravitation is. However, we can predict more things than Newton did… Even if he did not suspect they were there. This is just the beginning of what could be revealed, if our satanic impulses are kept in check.

Patrice Ayme’

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Artificial Turf At French Bilingual School Berkeley

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Patterns of Meaning

Exploring the patterns of meaning that shape our world

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in truth, only atoms and the void

West Hunter

Omnes vulnerant, ultima necat

GrrrGraphics on WordPress

www.grrrgraphics.com

Skulls in the Stars

The intersection of physics, optics, history and pulp fiction

Footnotes to Plato

because all (Western) philosophy consists of a series of footnotes to Plato

Patrice Ayme's Thoughts

Striving For Ever Better Thinking. Humanism Is Intelligence Unleashed. From Intelligence All Ways, Instincts & Values Flow, Even Happiness. History and Science Teach Us Not Just Humility, But Power, Smarts, And The Ways We Should Embrace. Naturam Primum Cognoscere Rerum

Learning from Dogs

Dogs are animals of integrity. We have much to learn from them.

ianmillerblog

Smile! You’re at the best WordPress.com site ever

Defense Issues

Military and general security

RobertLovesPi.net

Polyhedra, tessellations, and more.

How to Be a Stoic

an evolving guide to practical Stoicism for the 21st century

Donna Swarthout

Writer, Editor, Berliner

coelsblog

Defending Scientism

SoundEagle 🦅ೋღஜஇ

Where The Eagles Fly . . . . Art Science Poetry Music & Ideas

Artificial Turf At French Bilingual School Berkeley

Artificial Turf At French Bilingual School Berkeley

Patterns of Meaning

Exploring the patterns of meaning that shape our world

Sean Carroll

in truth, only atoms and the void

West Hunter

Omnes vulnerant, ultima necat

GrrrGraphics on WordPress

www.grrrgraphics.com

Skulls in the Stars

The intersection of physics, optics, history and pulp fiction

Footnotes to Plato

because all (Western) philosophy consists of a series of footnotes to Plato

Patrice Ayme's Thoughts

Striving For Ever Better Thinking. Humanism Is Intelligence Unleashed. From Intelligence All Ways, Instincts & Values Flow, Even Happiness. History and Science Teach Us Not Just Humility, But Power, Smarts, And The Ways We Should Embrace. Naturam Primum Cognoscere Rerum

Learning from Dogs

Dogs are animals of integrity. We have much to learn from them.

ianmillerblog

Smile! You’re at the best WordPress.com site ever

Defense Issues

Military and general security

RobertLovesPi.net

Polyhedra, tessellations, and more.

How to Be a Stoic

an evolving guide to practical Stoicism for the 21st century

Donna Swarthout

Writer, Editor, Berliner

coelsblog

Defending Scientism