Speed of gravity

[C1ay]

Can you tell me how to start a new thread?

From the list of forums, pick the appropriate forum for your thread and you will see a button labeled "New Thread" at the top of the forum.

[EWright]

From the list of forums, pick the appropriate forum for your thread and you will see a button labeled "New Thread" at the top of the forum.

 

:eek: Didn't I just say that? :rant: I'm thinking copyright suit here... :circle:

[EWright]

You're correct - the most recent, most popular theory (Expansion) make this.

 

Expansion is not a new discovery... think Hubble. It is the ACCELERATED expansion that is the new kid on the block and the basis of the latest predictions.

[CraigD]

Measuring one of an entangled pair of particles (usually but not limited to photons, or even to fundamental particles) allows you to know the state of the other regardless of how far they have been separated since their entanglement…

… However, it is my understanding (and i may be mistaken, and i'm not sure i'd agree with it) that quantum entaglement does require the two particles to have relayed the information required to define their relationship. The theory says that the pairs are not "ready made" as having opposite spins...

To the best of my understanding, it’s accurate to say the pairs aremade with opposite spins.

 

The only mechanism I can immediately recall that generates entangled pairs is when an electron absorbs a single photon, then emits 2 photons, not necessarily simultaneously. The 2 emitted photons will have opposite spins. Information about the original photons spin is lost.

 

There’s no “spin boson” in the standard model – no interaction that carries spin information between other particles. A particle’s spins is determined by the interaction that creates it. The interaction may determine the spin to be random.

but that only when you measure the spin of one particle, do you affect the spin of the other. They are not preprogramed, but directly affected by our influence in measuring the first particle and that the corresponding particle then instantly takes on the opposite spin regardless of distance.

Right. Which photon has up or down spin is not known until you measure one of the pair. What is preprogrammed is that the other will have the complimentary spin.

Theoretically, this distance could be billions of light years, and the affect would still be instantaneous. I have a hard time accepting this, but this is how it's been explained to me and how it is explain in Brian Greene's "The Fabric of the Cosmos" very explicitly

It’s a strange idea, but one supported by theory and, without exception, experimental evidence. Counterintuitive as it is, there seems to be no alternative to accepting it as physical fact.

 

I find that the strangeness of this “spooky action at a distance” is diminished when I consider what actually occurs in a quantum system when one makes a measurement. The quantum wave function of each particle changes, “renormalizing” the system to a new collection of values. This change is really to our knowledge of the system, not to its physical qualities. Although he quantum wave function describes the probability of the location and motion of the system’s particles over an arbitrary volume, it does not actually “exist” in that volume, so changes to it are not subject to any spatial metric, including being limited by c. Though not related, the quantum wave function feels to me much like the Platonic/Aristotelian Forms.

Expansion is not a new discovery... think Hubble. It is the ACCELERATED expansion that is the new kid on the block and the basis of the latest predictions.

Oops. Wrong term. I meant to write "(cosmic) Inflation".

 

This is not a particularly new theory, either - 1980s - but it seems to have morphed in a pretty continuous way into the 1990s versions that involve increased cosmic acceleration. They all seem very ad-hock, and have tried on variously occcasions but failed to insert their various "cosmological constant" force/interaction into the Standard Model. I wouldn’t be surprised if it all turns out to be incorrect.

 

I very much would be surprised if the Standard Model turns out to be wrong.

[EWright]

To the best of my understanding, it’s accurate to say the pairs aremade with opposite spins.

 

Logically, I would agree with you. If you can find information in regards to this, I would be very interested in it. But in Greene's description, the point that they are not preprogrammed is very key; and he goes to great lengths via metaphoric examples to explain that this is not the case.

[Erasmus00]

I find that the strangeness of this “spooky action at a distance” is diminished when I consider what actually occurs in a quantum system when one makes a measurement. The quantum wave function of each particle changes, “renormalizing” the system to a new collection of values. This change is really to our knowledge of the system, not to its physical qualities. Although he quantum wave function describes the probability of the location and motion of the system’s particles over an arbitrary volume, it does not actually “exist” in that volume, so changes to it are not subject to any spatial metric, including being limited by c.

 

Except that the wave function represents much more then just our knowledge. It actually does change the system when you make a measurement. This is the crux of Heisenberg's uncertainty. The wave function represents more then just our knowledge.

 

Consider a decaying partcle with a half life of t0. If you measure the system and it hasn't decayed, the particle is firmly in the "non-decayed" state and the clock must start over. Now imagine continuously making measurements. The particle never decays.

-Will

[CraigD]

Logically, I would agree with you. If you can find information in regards to this, I would be very interested in it. But in Greene's description, the point that they are not preprogrammed is very key; and he goes to great lengths via metaphoric examples to explain that this is not the case.

Greene’s description sounds accurate (I’ve not read “The Fabric of the Cosmos”, but I’m familiar with Greene’s style). It’s very important that the only information we have about the pair is that they have opposite spin. If this were not the case, entangled photons wouldn’t have the wave part of wave/particle duality, and wouldn’t produce such things as interference patterns. In fact, determining an entangled photon’s spin by measuring its partner’s will do just that. This is usually referred to as the “quantum eraser” experiment – there are many good descriptions of this – my favorite is the 1/1996 Scientific American article “Rubbed Out with the Quantum Eraser” (full text of article requires purchase or subscription – paper copy should be available in nearly any brick & mortar library)

[Aki]

A simple question came up to mind:

 

If the sun suddenly disappeared, what would happen first: the Earth would no longer feel the sun's gravitational attraction, or, the Earth would no longer receive light from the sun.

 

This all depends on the speed of gravity, of course. If gravity travels at c, then both events would happen at the same time. But I read somewhere that before light from the sun stops coming, the Earth should first drift off freely from the sun's attraction into space... I'm just confused.

[EWright]

A simple question came up to mind:

 

If the sun suddenly disappeared, what would happen first: the Earth would no longer feel the sun's gravitational attraction, or, the Earth would no longer receive light from the sun.

 

This all depends on the speed of gravity, of course. If gravity travels at c, then both events would happen at the same time. But I read somewhere that before light from the sun stops coming, the Earth should first drift off freely from the sun's attraction into space... I'm just confused.

 

It has since been 'decided' that both events would happen simultaneously and that gravity travels at the speed of c. But I've yet to hear an explanation as to why this would be.

[Bobby]

A simple question came up to mind:

 

If the sun suddenly disappeared, what would happen first: the Earth would no longer feel the sun's gravitational attraction, or, the Earth would no longer receive light from the sun.

 

This all depends on the speed of gravity, of course. If gravity travels at c, then both events would happen at the same time. But I read somewhere that before light from the sun stops coming, the Earth should first drift off freely from the sun's attraction into space... I'm just confused.

 

 

Sunlight takes about eight minutes to get from the sun to the earth. If the gravitational attraction of the sun disappeard and the earth started moving away from the sun, it would still take a considerable amount of time for it to be noticed by average folks. The earth orbits the sun at 18.5 MPS, or about 1,110 Miles per minute. So if the sun went away, the earth would move at a TANGENT to its original motion at a speed of 1,110 Miles Per Minute.

 

1,110 Miles Per Minute sounds pretty fast, but it isn't when compared to the speed of the planets. My guess is it would take a few hours before a noticeably effect would be seen by the average person.

[Erasmus00]

A simple question came up to mind:

 

If the sun suddenly disappeared, what would happen first: the Earth would no longer feel the sun's gravitational attraction, or, the Earth would no longer receive light from the sun.

 

This all depends on the speed of gravity, of course. If gravity travels at c, then both events would happen at the same time. But I read somewhere that before light from the sun stops coming, the Earth should first drift off freely from the sun's attraction into space... I'm just confused.

 

If general relativity is correct, the light will stop at the same time the gravity does. If you calculate the speed gravitational disturbances propagate at in GR, you get c.

-Will

[damocles]

Okay, most of this discussion is way beyond me.

 

So questions.

 

1. Where is the proof that gravity is a force instead of a mass induceed distortion of space?

2. What kind of experiment isolates the measure of gravity so that it is not confused with electro-magnetism?(I do not mean the dropping of objects. I mean such experiments as trying to measure the refraction of light in a gravitational field to set a measure for time retardation of the apparent refraction index.)

3. If gravity does not have a bounded velocity, then how is the principle of conservation of information not violated.(Hypermasses with escape velocities greater than c still put out information in the form of gravitational effects?)

4. If graviton interchange occurs between masses, (this makes sense to me as every other binding force has some kind of boson associated with it), has anyone devised an experiment for the observation of wave phenomena that should accompany such a boson?

5. Is the graviton asymmetric?

6. Can it be modulated?

 

Damocles

[EWright]

Okay, most of this discussion is way beyond me.

 

So questions.

 

1. Where is the proof that gravity is a force instead of a mass induceed distortion of space?

2. What kind of experiment isolates the measure of gravity so that it is not confused with electro-magnetism?(I do not mean the dropping of objects. I mean such experiments as trying to measure the refraction of light in a gravitational field to set a measure for time retardation of the apparent refraction index.)

3. If gravity does not have a bounded velocity, then how is the principle of conservation of information not violated.(Hypermasses with escape velocities greater than c still put out information in the form of gravitational effects?)

4. If graviton interchange occurs between masses, (this makes sense to me as every other binding force has some kind of boson associated with it), has anyone devised an experiment for the observation of wave phenomena that should accompany such a boson?

5. Is the graviton asymmetric?

6. Can it be modulated?

 

Damocles

 

My, for a discussion that you say is beyond you, you certainly proposed some pretty advanced questions. It is my understanding that gravity is indeed supposed to be a mass-induced warpage of space, but that it is still supposed to affect objects at the speed of c; though for no apparent reason.

 

I know of no such experiment, but I'd love to hear more.

 

I do not see how gravity can have a "velocity" if it doesn't travel; and I don't see how it can travel if it's an attractive force. What reattracts the traveling boson and that which it has attracted?

 

I do not see gravity as having any information that is transmitted. We can not, as far as I know, send gravitational messages. We may be able to tell the gravitational force of something by its affect on something else though.

[Aki]

Can the speed of gravity ever slow down? Light travels at a different speed when it is in a different medium, how about gravity?

[damocles]

I do not see gravity as having any information that is transmitted. We can not, as far as I know, send gravitational messages. We may be able to tell the gravitational force of something by its affect on something else though.

 

EWright

 

Okay, let me rephrase the question

 

3. If gravity does not have a bounded velocity, then how is the principle of conservation of information not violated.(Hypermasses with escape velocities greater than c still put out information in the form of gravitational effects?)

 

I made some kind of false assumption? That the tractor force which we measure between objects is akin to a property like particle charge or spin? If so, then let me say that I was thinking in terms of the information that is transmitted by that gravitational tractor-that is such things we can measure by observing the effects of gravitation such as angular momentum transfer between objects locked together in a two body common locus orbit.

 

Another property that could be measured by gravity under that conditional might be apparent inertia, but I should be cautious here as this is a mass-based property that manifests only when mass is accelerated and gravity is but one means by which mass is accelerated. You might also argue that in the case of angular momentum transfer.

 

So to get a pure gravitationally transmitted piece of information, I would have to find a property of the graviton that uniquely either increases or decreases the effect of gravitation between two objects locally without being congruent in effect to some other form of information transfer?

 

That is a tall order!

 

Only if we could somehow modulate the effects of gravity or screen the effects could we demonstrate that there was a gravitationally unique and specific piece of information?

 

Damocles

[paultrr]

The information that is transfered is location of mass. In all our studies of the cosmos while it is light itself that we use in such study, the different bodies of mass out there have left a signature behind that in short has transfered the position of where those bodies are. You might also do a bit of study of the subject of gravity waves in general.

[Jay-qu]

Can the speed of gravity ever slow down? Light travels at a different speed when it is in a different medium, how about gravity?

 

this is an excellent question! light is subject to refraction and is also distorted by gravity, so maybe there are some conditions that can distort and effect gravity...