Gravity waves analysis opens 'completely new sense'

spaceref.com ^ | 29 Oct 02 | Washington Univ

[RightWhale]

Gravity waves analysis opens 'completely new sense'

PRESS RELEASE

Washington University in St. Louis

St. Louis, MO. -- Sometime within the next two years, researchers will detect the first signals of gravity waves -- those weak blips from the far edges of the universe passing through our bodies every second. Predicted by Einstein's theory of general relativity, gravity waves are expected to reveal, ultimately, previously unattainable mysteries of the universe.

Wai-Mo Suen, Ph.D., professor of physics at Washington University in St. Louis is collaborating with researchers nationwide to develop waveform templates to comprehend the signals to be analyzed. In this manner, researchers will be able to determine what the data represent -- a neutron star collapsing, for instance, or black holes colliding.

"In the past, whenever we expanded our band width to a different wavelength region of electromagnetic waves, we found a very different universe," said Suen. "But now we have a completely new kind of wave. It's like we have been used to experiencing the world with our eyes and ears and now we are opening up a completely new sense."

Suen discussed the observational and theoretical efforts behind this new branch of astronomy at the 40th annual New Horizons in Science Briefing, Oct. 27, 2002, at Washington University in St. Louis. The gathering of national and international science writers is a function of the Council for the Advancement of Science Writing.

Gravity waves will provide information about our universe that is either difficult or impossible to obtain by traditional means. Our present understanding of the cosmos is based on the observations of electromagnetic radiation, emitted by individual electrons, atoms, or molecules, and are easily absorbed, scattered, and dispersed. Gravitational waves are produced by the coherent bulk motion of matter, traveling nearly unscathed through space and time, and carrying the information of the strong field space-time regions where they were originally generated, be it the birth of a black hole or the universe as a whole.

This new branch of astronomy was born this year. The Laser Interferometer Gravitational Wave Observatory (LIGO) at Livingston, Louisiana, was on air for the first time last March. LIGO, together with its European counterparts, VIRGO and GEO600, and the outer-space gravitational wave observatories, LISA and LAGOS, will open in the next few years a completely new window to the universe.

Supercomputer runs Einstein equation to get templates

Suen and his collaborators are using supercomputing power from the National Center for Supercomputing Applications at the University of Illinois, Urbana-Champaign, to do numerical simulations of Einstein's equations to simulate what happens when, say, a neutron star plunges into a black hole. From these simulations, they get waveform templates. The templates can be superimposed on actual gravity wave signals to see if the signal has coincidences with the waveform.

"When we get a signal, we want to know what is generating that signal," Suen explained. "To determine that, we do a numerical simulation of a system, perhaps a neutron star collapsing, in a certain configuration, get the waveform and compare it to what we observe. If it's not a match, we change the configuration a little bit, do the comparison again and repeat the process until we can identify which configuration is responsible for the signal that we observe."

Suen said that intrigue about gravity waves is sky-high in the astronomy community.

"Think of it: Gravity waves come to us from the edge of the universe, from the beginning of time, unchanged," he said. "They carry completely different information than electromagnetic waves. Perhaps the most exciting thing about them is that we may well not know what it is we're going to observe. We think black holes, for sure. But who knows what else we might find?"

[PatrickHenry]

Bump to a new reference frame.

God Bless America!
Bash the dems!

[Mr. K]

OK, and what about Bob Lazaar and the gavity-propulsion systems on the alien aircraft at area 51?

(hee hee- I was bored tonight so i thought this would stir the pot)

Seriously, though- his description is the only way I can imagine interstellar travel. Plus is is so darn fun to think about...

[Barry Goldwater]

Nope. One interesting thing though. Does Physicist's calculation for the energy of the gravitational wave from the revolving masses show it as a source or sink? If you calculated it using the equations for radiation from charge by substituting mass for q you wind up with negative energy flow, that is the "gravitational Poynting vector" for the gravitational and cogravitational field is directed inward. This makes sense since like charges repel and like masses attract. Now we have all these researchers spending tax dollars looking for gravitational waves radiated from distant bodies and they aren't seeing a thing. Hmmmm, I wonder why. As I said about cosmology and quantum physics....

[Physicist]

If you calculated it using the equations for radiation from charge by substituting mass for q you wind up with

...a mess, because the units would be hopelessly buggered, and because EM waves propagate as dipole fluctuations while gravitational waves propagate as quadrupole fluctuations, and because electromagnetism is a vector interaction while gravity is a tensor interaction, and so on.

negative energy flow, that is the "gravitational Poynting vector" for the gravitational and cogravitational field is directed inward.

Now you're confusing the field vector with the flow of energy.

You culled all this from the work of someone named Roland Dishington, you say? I'm afraid that all I've learned about him is that he served on the USC fencing team in the dismal 1941 season.

[longshadow]

dismal fencing season placemarker....

[PatrickHenry]

I found Dishington's name most prominently presented -- there are several pages devoted to him -- in my copy of "Famous Physicists of the 21st Century," but of course, I'm not permitted to share its contents with you.

[ncpastor]

It must be why I continue to get lumps in my gravy every danged time...

[Physicist]

dismal fencing season placemarker....

Punctured Trojan bump.

[DugwayDuke]

Perhaps you might wish to install a "gravity wave" dissipater. I got one on Ebay and I haven't had a problem with lumpy gravy since.

[anka]

"You know what you doing"?

[bribriagain]

Yes: some one set us up. The bomb.

[Barry Goldwater]

No this isn't from Roland Dishington. I just asked if you heard of him.

So is charge fixed to a moving dielectric considered a current? Is the electric field of this moving charge (that is, current) in the direction of the current density vector? Or is there no electric field of the charge in motion because it is mechanically forced to move?

I'm trying to do the Lorentz contraction calculation for the MM experiment. My problem is in determining the velocity of the apparatus. Is it just the tangential velocity at the earth's surface due to rotation or do I have to add the velocity of the earth going around the sun or also include the velocities of the solar system as well? What reference frame is used for the Lorentz contraction calculation? I'm confused because there is no relative motion between the observer and apparatus. Could you help me with this?

[PatrickHenry]

I'm trying to do the Lorentz contraction calculation for the MM experiment. My problem is in determining the velocity of the apparatus. Is it just the tangential velocity at the earth's surface due to rotation or do I have to add the velocity of the earth going around the sun or also include the velocities of the solar system as well? What reference frame is used for the Lorentz contraction calculation? I'm confused because there is no relative motion between the observer and apparatus. Could you help me with this?

If I recall correctly, the original MM idea was to determine if the motion of the earth, relative to the presumably stationary aether, made any difference in the transit time of the light beams. The motion of the entire solar system, and the galaxy, etc., would be common features to any such measurement, and could thus be ignored.

[Physicist]

So is charge fixed to a moving dielectric considered a current?

Yes.

Is the electric field of this moving charge (that is, current) in the direction of the current density vector?

No. In fact, Lorentz contraction causes the electric field from a moving charge to become weaker along the axis of motion and stronger in the transverse direction. The field becomes compressed along the axis of motion.

If you think carefully--very carefully--about this, it might seem that this gives rise to a situation that is not Lorentz invariant: as the charge passes by a "stationary" test charge, a stationary observer should expect the test charge to be subjected to a greater electostatic force than would be measured by an observer that is comoving with the moving charge. What's a test charge to do?

As it turns out, this difference in force is exactly compensated by the magnetic field that is observed by the stationary observer, created by the motion of the moving charge. This field is not observed by the comoving observer. They agree on the net motion of the test charge.

In other words, the magnetic field is the manifestation of effect of Lorentz contraction and time dilation upon an electric field. It's relativity you can play with at home.

Or is there no electric field of the charge in motion because it is mechanically forced to move?

The total electric field around the charge is invariant. Gauss's Law, once again. There is no additional electric field that is created by the movement of the charge. Battery, black hole, or baseball bat, it doesn't matter what causes the charge to move. The divergence of the field equals the charge density, end of story.

I'm confused because there is no relative motion between the observer and apparatus.

Then that's the frame you use for that observer. The issue is that a moving observer will also have to observe a null result for that apparatus. It has to work in all possible reference frames. The different observers aren't entitled to disagree about the outcome of the experiment; either the interference fringes shift or they don't. They will, however, disagree about the size of the interferometer.

[Barry Goldwater]

I'm assuming, as Physicist said, that the Lorentz contraction can be measured from the MM experiment. I'm having trouble with the v/c term. What v do I use? Are you saying v is zero? If it's zero, then where is the contraction? There's no relative motion between the light source, apparatus and observer. What is the causitive agent of the contraction?

[Barry Goldwater]

So is charge fixed to a moving dielectric considered a current?
Yes.

Is the electric field of this moving charge (that is, current) in the direction of the current density vector?

No. In fact, Lorentz contraction causes the electric field from a moving charge to become weaker along the axis of motion and stronger in the transverse direction. The field becomes compressed along the axis of motion.

>>I'm familiar with the bunching of the electrostatic field lines on moving charge. I'm talking about the E aligned with the current density vector, not the coulombic E .


If you think carefully--very carefully--about this, it might seem that this gives rise to a situation that is not Lorentz invariant: as the charge passes by a "stationary" test charge, a stationary observer should expect the test charge to be subjected to a greater electostatic force than would be measured by an observer that is comoving with the moving charge. What's a test charge to do?

As it turns out, this difference in force is exactly compensated by the magnetic field that is observed by the stationary observer, created by the motion of the moving charge. This field is not observed by the comoving observer. They agree on the net motion of the test charge.

>>Correctly stated it is the changing magnetic field.

In other words, the magnetic field is the manifestation of effect of Lorentz contraction and time dilation upon an electric field. It's relativity you can play with at home.

Or is there no electric field of the charge in motion because it is mechanically forced to move?

The total electric field around the charge is invariant. Gauss's Law, once again.

>> The E field due to charge motion has zero divergence, just as the current density vector. This cancels out when gauss's law is applied. There's an "inny" and an "outy" on that vector over the closed surface.

There is no additional electric field that is created by the movement of the charge. Battery, black hole, or baseball bat, it doesn't matter what causes the charge to move. The divergence of the field equals the charge density, end of story.

>>The divergence definitely equals the charge density. The current density has zero divergence and the E field aligned with J also has zero divergence. If div J did not equal zero charge would be accumulating

I'm confused because there is no relative motion between the observer and apparatus.

Then that's the frame you use for that observer. The issue is that a moving observer will also have to observe a null result for that apparatus. It has to work in all possible reference frames. The different observers aren't entitled to disagree about the outcome of the experiment; either the interference fringes shift or they don't. They will, however, disagree about the size of the interferometer.

>>Agreed. But if I'm in the same frame then v = 0. You said the MM apparatus has measured the Lorentz contraction. I'm just trying to figure out how and contraction from what?

[anka]

"Move Zig". "For great justice"!

[PatrickHenry]

I'm assuming, as Physicist said, that the Lorentz contraction can be measured from the MM experiment. I'm having trouble with the v/c term. What v do I use? Are you saying v is zero? If it's zero, then where is the contraction? There's no relative motion between the light source, apparatus and observer. What is the causitive agent of the contraction?

I believe that v was the velocity of the frame of reference (that is, the earth) in its motion around the sun.

[Physicist]

The E field due to charge motion has zero divergence, just as the current density vector.

There is no E field that is due to the motion of the charge. None whatsoever. I don't know what put that notion into your head.

You said the MM apparatus has measured the Lorentz contraction.

Yes. You measure the speed of light and time dilation in each frame with respect to the other. You predict from that a certain shifting of the interference fringes. You observe no such shift, so you can calculate how much the device must have shrunk to compensate.

I'm just trying to figure out how and contraction from what?

The contraction is due to the perspective from different inertial frames. A person looking at a yardstick from the side will see it as a long object, while a person looking at it from the end will see it as a short object. The Lorentz transformation is analogous to this effect of rotation, except that it describes a transformation between space and time, rather than the rotation of one space axis into another.

[Barry Goldwater]

One thing to consider about the moving electron is that the E field lines do not bunch at the point perpindicular to its motion and continue off into space in straight lines. If this were true, then the field from an electron would "move out" instantaneously. Rather the field lines resemble fluid streamlines, they curve opposite the velocity vector. The curvature is proportional to the speed.
Now, if they curve opposite the velocity, what would be the resultant E vector? Its divergence.
If the moving electron is considered a current of density J and it is moving at a high velocity so almost all the E field lines are perpindicular to the motion, then the work done on this particle: Integral E dot J is zero. The work done decreases as the velocity gets increases. Reliable model isn't it? Perhaps the field lines are confused with the dimensional Lorentz contraction of the electron.

If an electric field causes charge to move (the charge moves to establish an electric field of its own that counters the impressed field), then why is this field of the charge absent when the particle moves due to forces other then electric fields? The field exists only in the vicinity of the charge.

I'm trying to find a reference for you on this that is not proprietary. There may be something in electrohydrodynamics, frictional electrification or in the atmospheric sciences.