All interrelated and subject to the constant speed of light.
Nowhere is stated the Calabi-Yao. A deficit article, imo."
Yes and no. Calabi-Yao is just an area that has neither space nor time, correct?!
Posted on 01/07/2003 6:23:34 PM PST by forsnax5
The speed of gravity has been measured for the first time. The landmark experiment shows that it travels at the speed of light, meaning that Einstein's general theory of relativity has passed another test with flying colours.
Ed Fomalont of the National Radio Astronomy Observatory in Charlottesville, Virginia, and Sergei Kopeikin of the University of Missouri in Columbia made the measurement, with the help of the planet Jupiter.
"We became the first two people to know the speed of gravity, one of the fundamental constants of nature," the scientists say, in an article in New Scientist print edition. One important consequence of the result is that it places constraints on theories of "brane worlds", which suggest the Universe has more spatial dimensions than the familiar three.
John Baez, a physicist from the University of California at Riverside, comments: "Einstein wins yet again." He adds that any other result would have come as a shock.
You can read Fomalont and Kopeikin's account of their unique experiment in an exclusive, full-length feature in the next issue of New Scientist print edition, on sale from 9 January.
Isaac Newton thought the influence of gravity was instantaneous, but Einstein assumed it travelled at the speed of light and built this into his 1915 general theory of relativity.
Light-speed gravity means that if the Sun suddenly disappeared from the centre of the Solar System, the Earth would remain in orbit for about 8.3 minutes - the time it takes light to travel from the Sun to the Earth. Then, suddenly feeling no gravity, Earth would shoot off into space in a straight line.
But the assumption of light-speed gravity has come under pressure from brane world theories, which suggest there are extra spatial dimensions rolled up very small. Gravity could take a short cut through these extra dimensions and so appear to travel faster than the speed of light - without violating the equations of general relativity.
But how can you measure the speed of gravity? One way would be to detect gravitational waves, little ripples in space-time that propagate out from accelerating masses. But no one has yet managed to do this.
Kopeikin found another way. He reworked the equations of general relativity to express the gravitational field of a moving body in terms of its mass, velocity and the speed of gravity. If you could measure the gravitational field of Jupiter, while knowing its mass and velocity, you could work out the speed of gravity.
The opportunity to do this arose in September 2002, when Jupiter passed in front of a quasar that emits bright radio waves. Fomalont and Kopeikin combined observations from a series of radio telescopes across the Earth to measure the apparent change in the quasar's position as the gravitational field of Jupiter bent the passing radio waves.
From that they worked out that gravity does move at the same speed as light. Their actual figure was 0.95 times light speed, but with a large error margin of plus or minus 0.25.
Their result, announced on Tuesday at a meeting of the American Astronomical Society meeting in Seattle, should help narrow down the possible number of extra dimensions and their sizes.
But experts say the indirect evidence that gravity propagates at the speed of light was already overwhelming. "It would be revolutionary if gravity were measured not to propagate at the speed of light - we were virtually certain that it must," says Lawrence Krauss of Case Western Reserve University in Cleveland, Ohio.
That's how you can spot the kooks even when they wear the best camo--the college degree.
Perfectly.
If that is a correct notion, the question then becomes, what about mass causes this 'field' influencing other masses?
To be precise, it's energy that creates the gravitational field, not mass per se. In practice, mass is far and away the most significant concentration of energy in any physical system.
... Don't physicists define the 'thing' causing the influence, creating the field, 'gravitons'? And if there are gravitons, doesn't it appear that these gravitons are actually influencing the spacetime of the universe (the background field in which masses exist), and that affected spacetime is that which then acts upon the other mass(es)?
This is a tricky question to answer, because we don't know much about gravitons. We simply do not have a viable quantum theory of gravity. So I will confine my answer to General Relativity.
The gravitational field (per GR) is a curvature of spacetime. You are correct that the field is fixed with respect to the object (provided that the object does not undergo an acceleration). The field itself does not propagate, although changes in the field (caused by the acceleration of the object) do. Objects moving through the field will "see" the same field, because it is fixed with respect to the spacetime points through which the objects move (wholly unlike such subjective quantities as the angle of incidence for incoming photons, which gives rise to stellar aberration).
[Geek alert: Special Relativity dictates that the field seen by two observers with a relative velocity will be slightly different, but this is a subtle effect compared to what is being claimed by the "infinite speed of gravity" crowd. The Lorentz invariance is maintained because a compensating field (the "gravitomagnetic force") arises. This force is directly analogous to the magnetic force in electromagnetism. It arises for the same reason, but it has a much different form.]
You're not, really. The fields are just as free to undergo relative motion as the particles to which they are bound.
But what I would like to address is the possibility that the field of spacetime is influenced by the space and time bound up in mass. I'm not so much addressing discrete physical quanta, as in 'particles' of gravity, as I'm trying to address the notion of 'dimensional quanta' (wound up dimensional phenomena) bound up in discrete physical phenomena you call sub-atomic particles.
I don't really understand what you're trying to say, here; the notion of dimensions being bound up into physical particles makes little sense to me, I'm afraid.
Here's as near as I can come. Surely you've heard of "superstrings", the darlings of the popular press. These are one-dimensional objects that assume specific topological paths through an 11- or 26-dimensional space, of which all but 3+1 dimensions are "compactified" into a very tiny radius. In this scheme, a graviton would be a little loop through that space.
In some models, one or more of the "compactified" dimensions is much larger than the others. In this case, we can end up with a whole series of distinct types of gravitons with different masses! Some graviton strings might pass around the "large" extra dimension once before meeting back up with itself, some twice, some three times, or more. They can't transform into one another for topological reasons. But this additional length in the extra dimension allows it to have a significant momentum component along the extra dimension, which manifests itself in our 3+1 dimensional space as mass. Therefore, one prime experimental signature for "large" extra dimensions is the presence of such a series of heavy particles, known as a "Kaluza Klein tower of gravitons".
Yes, but with our present equipment, I'm guessing that it takes something as massive as Jupiter to get any useful data. Still, it could have been done earlier, as you say.
Yes and no. Calabi-Yao is just an area that has neither space nor time, correct?!
"Uh, oh! Looks like somebody's forgotten that all motion is relative." - Physicist
Wow, where do I start? Your comment is more than just wrong, it's wrong in multiple dimensions.
For one thing, acceleration and deceleration are NOT relative (hey, decelerate objects, even uniformly, enough and you will see the temperature of those objects drop to Absolute Zero, too cool).
For another thing, motion, even when relative between two objects (e.g. uniform), still matters.
And that fact brings us back to my point and away from your red herring statement above.
Consider, for instance, that our Sun and Earth are BOTH moving in the same direction as the rest of our Solar System, and that our Solar System is moving in uniform concert with the rest of our Galaxy (which itself is moving through our Universe).
Now, even though the relative motion of the Earth and the Sun would APPEAR to make the Sun seem stationary as the Earth orbits around it, in reality the Sun (as well as the Earth) will be in a different physical location in the 8.3 minutes that it takes light to reach the Earth.
Thus, observers on Earth will currently percieve the Sun to be in the location it occupied 8.3 minutes ago.
This brings up an interesting consideration: does the Earth orbit around the ACTUAL position of the Sun (implying a near instantaneous speed of gravity as predicted by Newton), or does the Earth orbit the PERCIEVED position of the Sun (implying a speed of Gravity equal to that of Light as predicted by Einstein)?
If the Sun and the Earth (OK, our whole Solar System) are both moving North at the same speed even as Earth orbits the East-West axis of the Sun, then both the Sun and the Earth will be 8.3 minutes North of the percieved position of the Sun (due to the 8.3 minute delay for light reaching the Earth from the Sun).
Thus, planetary orbits based on a speed of Gravity at that of the speed of Light will have a "lag" South of the Sun (and this "lag" will be more pronounced the further away fromt he Sun that a planet orbits), whereas planetary orbits based upon a speed of Gravity equal to the Speed of Light squared will have no discernable lag South of the uniform movement of our Solar System.
Thus, if Jupiter lags further South of the Sun than does Earth, then you and the authors of the article for this thread are correct.
On the other hand, if the planets generally orbit the Sun in the same plane (i.e. there is no lag South of the Sun by the planets), then Gravity must travel substantially faster than the speed of Light.
That's wrong.
The Sun, Earth, and the rest of our Solar System ARE moving, it's just that they are moving uniformly, so even as the Earth orbits the Sun, both the Earth and the Sun are simultaneously moving together in yet another direction.
This is easy to visualize if you have a toy model of our Solar System. Place that toy model on a ship and start the ship moving. Now, the Earth will circle the Sun in that toy model, but in 8.3 minutes the entire model will be in a new position due to the movement of the ship. However, to an observer on the Earth of that toy model, the Earth would merely have revolved a little around the Sun, while the Sun remained stationary.
Of course, we know that since the ship moved during that time period, that the Sun is actually in a new position. A GPS unit would record two different positions for our toy model, after all.
Likewise with our actual Solar System, one could visualize the entire System moving North/Vertical/towards Polaris for the purposes of a thought exercise. However, just like the toy model on the ship in the example above, whereas an Earth-based observer would percieve that the Sun was in the same position no matter how much time had passed, in reality we know that the Sun will be in a new position above its old location.
And because we know that our Sun is moving North over time, we can discern if Gravity has the same delay as Light simply by detecting if the Earth is orbiting the actual or the perceived (i.e. the "old") position of the Sun.
Nonsense.
What I said was that Gravity easily bends Light (e.g. thumb experiment, Black Holes, etc.), but that Light did not appreciably bend Gravity.
I also said that one would be more inclined to attribute such a discrepancy (i.e. one bends the other but not vice-versa) to a large difference between the two, such as a large difference in their speed.
What university taught you that our Solar System was stationary?
Name it so that I can get their accreditation pulled.
Troll me once, shame on you, troll me twice, shame on me.
Quick, Troll, point out where I said that the "Solar System was stationary". I didn't. I said that the *Sun* was stationary relative to the Earth's orbit (and the rest of the Solar System), and indeed it is. Even a child should have gotten a clue from the way I wrote:
"The Sun doesn't go zooming around the solar system. It sits right there in the middle, century after century."Stop trolling -- I caught onto your weird hobby several threads ago, and it only torpedoes your own credibility.
And your attempt to re-troll by again pretending to believe that gravitation causes diffraction ("you can see that Gravity bends Light by simply holding your thumb between your eye and a light source and looking at the edges"), when I already debunked that, is just pitiful. Most trolls at least are able to come up with new material instead of recycling their past failures.
You're not fooling anyone here, except maybe yourself.
Claiming that all you've said is that the Sun remains not actually in the same place but rather relatively in the same place might save a little face with a few uneducated lurkers, but any thinking, educated person will quickly realize that your new "point" is meaningless because we are talking about the Sun actually moving.
And contrary to your earlier claims and insinuation, the Sun (as does the rest of our Solar System) is forever moving through the universe.
The Sun does NOT sit still. Sure, it can be conceptually thought of as being a stable point around which the planets orbit, but that's only because the planets are likewise moving through the universe uniformly with the Sun.
But the Sun is in a DIFFERENT location today than it was yesterday (simply because it is traveling along with the rest of our Solar System through the universe), and the Sun of tomorrow will be in a position different than the Sun of today, and so on and on and on...
This includes the fact that the Sun is in a different position 8.3 minutes ago than when we see it, due to the fact that it takes Light 8.3 minutes to reach the Earth.
This means that the Sun which we "see" is actually the Sun 8.3 minutes ago.
And if the Solar System is moving due North toward Polaris, then the Sun that we "see" is 8.3 minutes South of the actual position of the Sun itself due to that delay in Light reaching the Earth from the Sun.
Moreover, this delay INCREASES the further out that each planet orbits the Sun.
Now, if Gravity travels at the SAME speed as Light, then the planets will not only have that same gravitational/orbital delay, but they will also orbit around their PERCIEVED Sun rather than around the actual Sun, due to the delay in Gravity.
But of course, we already know that the planets don't have such a delay/lag in their orbits; in other words, we know that Gravity travels much faster than the speed of Light because the planets do not increasingly lag South of the actual position of the Sun as their orbits increase in distance from the Sun.
Since the Sun ISN'T ACTUALLY MOVING, its gravity signature, and even its visual appearance via light, REMAIN THE SAME whether we're seeing it as it was a nanosecond ago, 8.3 minutes ago, or six months ago -- from *any* vantage point.
Furthermore, the "apparent position" of the Sun in the sky is due to the Earth's rotation, which is a LOCAL situation, and independent of any delay in light/gravity propagation from the Sun -- in simple terms, the only thing that would make the Sun look 8.3 minutes ahead or behind of its apparent position in the sky would be a change in the Earth's rotation itself, *not* any delay in light coming from the Sun.
So yes, please, tell me what *I've* missed...
I also eagerly await your supporting evidence for your amazing claim that there are "measurements of earth's acceleration toward the sun that show a direction that is 8.3 minutes ahead of the apparent position of the sun in the sky".
76 posted on 01/08/2003 1:49 AM CST by Dan Day
What an interesting thing to get caught saying...
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