Speed of..................gravity!

[TheMightyKong]

Who is Gravity? And while I'm at it why is einstein? And when is jupiter?

[thing]

Hi Ian here is my message..

First begin by knowing what is gravity. Gravity is the mutual attraction of objects about each other and in other words is the force of attraction that exists between all particles with mass in the universe. Well it is true that gravity has a speed but it's all very concerning because changes and masses of particles and energy from stars to planets so. Soon it would be very uniform know the speed of gravity in a black hole for example the speed of escape (320000m / s) exceeds the speed of light (around 300000m / s). For example if you were on Mars the force of gravity was different, the earth and mercury too. The matter black or invisible matter is not explicitly for sure but it has a high density and gravity exerts on other bodies such as the galaxies since this component comprises 90% of the mass of the universe and 23% of the energy that once the gravity is something very Very concerning if you wanted to calculate the value of gravity on earth was very difficult to measure because you approach the core of the planet and the severity will be greater if you throw in a building the speed of gravity is increased as the weight to fall on earth will be something like 20 times your weight when you fall. So to learn the value of gravity is very difficult if not virtually impossible because many factors have been around this. We managed to learn the speed of a black hole because the speed at the core of this and exactly the same as if it were a little further because it is very items. And finally something simple such that we still have strength in space because gravity that we have bodies who exercise power over each other or energy. As we depart from energy to gravity force will become increasingly void as it is close to zero forces. I hope I have helped John Christ.

Summed it up nicely there John.

[supernova]

Hi Ian here is my message..

First begin by knowing what is gravity. Gravity is the mutual attraction of objects about each other and in other words is the force of attraction that exists between all particles with mass in the universe. Well it is true that gravity has a speed but it's all very concerning because changes and masses of particles and energy from stars to planets so. Soon it would be very uniform know the speed of gravity in a black hole for example the speed of escape (320000m / s) exceeds the speed of light (around 300000m / s). For example if you were on Mars the force of gravity was different, the earth and mercury too. The matter black or invisible matter is not explicitly for sure but it has a high density and gravity exerts on other bodies such as the galaxies since this component comprises 90% of the mass of the universe and 23% of the energy that once the gravity is something very Very concerning if you wanted to calculate the value of gravity on earth was very difficult to measure because you approach the core of the planet and the severity will be greater if you throw in a building the speed of gravity is increased as the weight to fall on earth will be something like 20 times your weight when you fall. So to learn the value of gravity is very difficult if not virtually impossible because many factors have been around this. We managed to learn the speed of a black hole because the speed at the core of this and exactly the same as if it were a little further because it is very items. And finally something simple such that we still have strength in space because gravity that we have bodies who exercise power over each other or energy. As we depart from energy to gravity force will become increasingly void as it is close to zero forces. I hope I have helped John Christ.

Summed it up nicely there John.

for me :thumbright: For you.

[ollypenrice]

To take a wee step back on the subject of gravity, the whole point of Einstein's analysis is that you don't have to think of gravity as a force. It is a field. When a comet flies towards the sun it enters a gravitional field (a curvature of spacetime) which is already there and it behaves accordingly. This addresses the problem of which Newton was aware; how can the Earth and the moon send out an instananeous force of attraction between each other. He didn't like this implication of his own theory and he was right not to.

Don't listen to me, I used to be an English teacher!

Olly.

[Froobyone]

Hi, I know I'm new here, but this is the sort of thing I've been pondering of late.

The thinking that gravity is a wave and emanates from each body, at the speed of light, seems to be the current view.

But I wonder, if gravity exists instantly.

It has been posted that for this to happen, information would have to be exchanged faster than the speed of light, which Albert said was impossible.

I'm not so sure.

Information can be exchanged between particles in ways we simply cannot comprehend.

Take for example Wolfgang Pauli’s Exclusion Principle of 1925, that the subatomic particles in certain pairs, even when separated by the most considerable distances, can each instantly “know” what the other is doing. Particles have a quality known as spin and, according to quantum theory, the moment you determine the spin of one particle, its sister particle, no matter how distant away, will immediately begin spinning in the opposite direction and at the same rate.

Apologies for quoting that directly from a book, but it explains it a lot better than I can.

In one experiment, two particles where sent 7 or 8 miles away from each other, which in particle terms, isn't like popping to the post office.

When one of the particles was "interfered" with the other reacted instantaneously. Though, I don't have the details on exactly how the scientists "interfered" with it; But I believe there's a big court case and the particle, who can't be named for legal reasons, is sueing.

So that shows that information at the quantum level travels very quickly indeed and in inexplicable ways.

So the possibilty exsists that some things can move faster than light.

So let's think about about light for a second.

We know how fast light is, but do we know why it's that fast? If light is the benchmark that can't be broken, why is it capped there? What is, in fact, stopping light from being everywhere at once?

I don't believe in God or Intelligent Design (but others are free to). So this figure for the speed of light came from something, and obviously it's useless to think of it as x miles an hour. Measuring something as fundamental as light using our own made up measuring scales tells us nothing.

What we need to do, is find out how the universe measures the speed of light, because that number, whatever it is, is significant.

Oh and another thing, I think it's gravity that affects time, not speed. The greater the gravity, the slower time moves. The storms on Jupiter haven't lasted 300 years, it just looks like they have because the time/light is all bunched up?

While I'm at it, Einstein was right about one thing (oh all right, considerably more than one thing) time is relative to the obsverver. Take us for example, we think things take a long time, planets forming, life evolving, suns using all their fuel, but complared to a lifetime that lasts, if you're lucky 80 years, then yeah, things take a long time. But for all we know, at a different scale, the universe is moving incredibly fast; Stars form, go critical and die like a flash bulb.

Ok the example is an huge exageration, but it is known, that different animals percieve time differently to us. Flies see our world in slow motion, that's why they can get out of the way of a casual swat. It's easy to dodge a car coming at you at 1mph, just as the fly sees the hand coming at it as a slow moving object.

I'm not an expert, but I think Tortoises see our world speeded up, which just backs up my theory that Tortoises are sneaking joints when we're not looking.

Anyway, I think I've said enough. I hope people can kindly put me right on any errors I've made.

Be well.

Dan

Inside every old person is a young person wondering what happened.

[Steve922]

The original question remains:- Has the speed of gravity actually been measured? Or is there any practical evidence to suggest what it might be?

Steve

[darditti]

Don't listen to me, I used to be an English teacher!

A polymath, I would say. And no mean cook either.

David

[darditti]

Has the speed of gravity actually been measured? Or is there any practical evidence to suggest what it might be?

According to the theory of General Relativity, a change in a gravitational field (which might occur, e.g., when a supernova explodes) propagates at the speed of light. This is what is known as a gravity wave. These have not so far been detected, so, no, we have not directly measured the speed of gravity waves, if that is the question. But so many other experimental checks of General Relativity have confirmed its validity that it seems pretty solid. As Olly points out, it is not necessary for an unchanging gravitational field (e.g. that of the Sun) to have any "speed". [br][br]As to the speed of light itself, it is simply a measured number. It has to have a value, and it has the one it has. The fact that no other transfer of information can exceed the speed of light is, it seems to me, an experimental fact, on which relativity is based, it is not a conclusion arising out of the theory. The theory does not prove that nothing can travel faster than light, and much theoretical work has been done on the basis that there could be faster than light particles. All we can say is that relativity has not failed any tests of measurement so far, and we have no evidence of faster than light information transfer in the Universe on the macro scale. [br][br]I will not get into interpretations of quantum theory, and how compatible these are with relativity, as this is a hornets' nest. Lots of interesting stuff on Wikipedia if you want to explore.[br][br]David

[timetraveller]

Gravity is nothing more than the gradient of the curvature of space and as such is an effect of mass rather than a force the bigger the mass the greater the gradient or the curve becomes up to the point of the creation of a black hole were the gradient reaches an angle so steep that it is imposible to ever reach either escape velocity or orbital velocity which is why even light cannot escape .The photons even at light speed are not fast enough to reach orbital velocity let alone escape velocity simple when you think about it

regards Pete

[Tiny]

So - how do we get to the answer - 42 - from this?

[timetraveller]

maybe 42 degrees is the universal gradient

[acey]

Rainbows have an angular radius of 42 degrees - this is surely significant.

Time must be somewhere over it...

[acey]

No, hang on, forget Douglas Adams - it was all worked out by Thomas Pynchon:

http://www.amazon.co.uk/Gravitys-Rainbow-Thomas-Pynchon/dp/0099533219/

[Planet Guy]

Or, is it able to be measured?

There is a way the scientist guys are trying to measure gavity waves. It's called a Laser Inferometer (from memory) and works by firing lasers down two tunnels at right angles. Gravity waves distort matter, and a passing gravity wave deflects the laser. Scientists detect a movement in the laser beams and so meaure a gravity wave. By measuing the difference in time from when the wave hits the first laser beam and the second laser beam, they can claculate the speed of a gravity wave.

I've attached a very simple diagram to maybe help explain the stuff I explained.

If I am wrong, somebody please correct me, this is from memory.

[acey]

I don't see the diagram but your explanation is correct. Gravity waves will change the length of an object measured along two axes at right angles - this change is detected by the relative phases of the beams.

[Planet Guy]

lol, yeah forgot diagram.

[BlueAstra]

If gravity travels at c, how does one side of a galaxy react and know what is happening at the other side, which could be millions of light years away? I thought mass warped spacetime, which affects the movement of real objects; like balls rolling over peaks and valleys. Gravity therefore affects the framework that everything hangs from.

[vhbelvadi]

GRAVITY HAS NO SPEED!

How can ANY force have speed?

[Matthew.Blake]

GRAVITY HAS NO SPEED!

How can ANY force have speed?

If I push you I have exerted a force on you.

If I exert a force on you I am passing information to you (in this case the information I am pushing you).

If I pass information it must have some form of courier.

A courier must have a speed.

Similarly,

If a planet moves, the gravitational field it generates changes.

Those changes must somehow be communicated to the distant objects it affects.

The communication again happens by some courier which again must have a speed.

Not just any force has a speed, EVERY force has a speed.

[narrowbandpaul]

the force doesnt change....a force has no speed.

the force carrier moves at a speed.

when the thread says speed of gravity, it actually means, the speed at which the gravitational force propogates.

forces dont have speeds, the particles that carry them do.

the graviton is the theorised force carrrier for gravity. It is massless and has a spin of 2. It therefore travels at the speed of light.

gravitational forces propogate at c.

if the sun were removed from its position now, we wouldnt experience the effect for 8minutes....

if it was instantaneous, then we would feel the effect before light had chance to get there. So wouldnt wouldnt see that anything was wrong, yet we would be flying tangential to our orbit.

if gravitational signals travel at c. Then the gravitational force arrives at the same time as the light. Therefore we fly tangential to our orbit only once we see that the sun has been removed.

[vhbelvadi]

If I push you I have exerted a force on you.

If I exert a force on you I am passing information to you (in this case the information I am pushing you).

If I pass information it must have some form of courier.

A courier must have a speed.

Similarly,

If a planet moves, the gravitational field it generates changes.

Those changes must somehow be communicated to the distant objects it affects.

The communication again happens by some courier which again must have a speed.

Not just any force has a speed, EVERY force has a speed.

Ultimately, it's just the source of the force that has speed.

But what about contact forces? And how would you explain all this when the net force remains zero?

[Matthew.Blake]

Ultimately, it's just the source of the force that has speed.

But what about contact forces? And how would you explain all this when the net force remains zero?

That's just the electromagnetic force so the courier is a bunch of photons constantly exchanging momentum between the two objects in contact.

[vhbelvadi]

That's just the electromagnetic force so the courier is a bunch of photons constantly exchanging momentum between the two objects in contact.

I don't get you.

[Matthew.Blake]

What stops a cup sinking through a table?

The individual atoms in the table and the cup cannot touch, something different would happen then. Instead the positive nuclei of atoms repel each other, the electrons are too diffuse to have a significant effect.

[vhbelvadi]

What stops a cup sinking through a table?

The individual atoms in the table and the cup cannot touch, something different would happen then. Instead the positive nuclei of atoms repel each other, the electrons are too diffuse to have a significant effect.

Got it!

Thanks.