The motion of the bodies is relevant because it impacts distance which in turn impacts the strength of a field (read: force of Gravity) which in turn gives us a time lag to measure before a peak field strength is achieved at any given point.
Posted on 11/09/2005 1:41:45 PM PST by aculeus
Many expect it to be one of the biggest scientific breakthroughs of our age: "There'll certainly be a Nobel Prize in it for somebody," says Jim Hough.
The UK professor is standing on a farm road in Lower Saxony, Germany, with a crop of beet on one side and sprouts on the other.
But the real interest lies at his feet - with some shabby, corrugated metal sheeting. For a moment, it looks like an upturned pig trough until you realise it stretches for hundreds of metres.
The sheeting hides a trench and, within it, the vacuumed tube of an experiment Hough believes will finally detect the most elusive of astrophysical phenomena - gravitational waves.
The Glasgow University scientist has been chasing these "ripples" in space-time for more than 30 years and feels certain he is now just a matter of months away from bagging his quarry.
"It will be a big event for two reasons: it will be yet another confirmation that Einstein's Theory of General Relativity is correct, but it will also open up a new kind of astronomy that will allow us to look inside the most violent events in the Universe."
A new kind of astronomy requires a new type of "telescope", and that's just what Hough and UK-German colleagues have been developing on farmland a short drive from Hanover. It is called GEO 600.
Stretch and squash
Its looks are deceptive. Anonymous silver shacks house state-of-the-art electronics and a high-power laser.
And then there is that trench - two in fact, running out at right-angles to each other for more than half a km. Their vacuum tubes end in super-smooth mirrors slung by pure-glass wires from damped frames. This is precision engineering at the extreme. To have any hope of detecting gravitational waves, it has to be.
Unlike electromagnetic waves - the light seen by traditional telescopes - gravitational waves are extremely weak. If one were to pass through your body it would alternately stretch your space in one dimension while squashing it in another - but the changes are fantastically small.
Any moving mass will send gravitational waves radiating outwards at the speed of light; but only truly massive bodies, such as exploding stars and coalescing neutron stars, can disturb space-time sufficiently for our technology to pick up the signal.
"The displacement sensitivity of GEO 600 is one three-thousandth of the diameter of a proton," explains Professor Karsten Danzmann, from the Albert Einstein Institute and Hanover University.
"Put another way, it's equivalent to measuring a change of one hydrogen atom diameter in the distance from the Earth to the Sun."
And it is these tiny deviations that GEO 600 hopes to measure in the laser light it bounces through its L-shaped tubes.
Cosmic symphony
Careful refinement and tuning of the instrumentation has moved the installation very close to the required sensitivity - towards a possible "eureka" moment.
The UK-German team is working with US colleagues who have two similar facilities known collectively as Ligo - Laser Interferometer Gravitational-Wave Observatory.
These set-ups, at Livingston in Louisiana and Hanford in Washington, employ laser arms that are 4km long. Both Ligo and GEO 600 are to begin a full "science run" in November, with the aim of gathering data continuously for 18 months. In that time, they would expect to see perhaps two events, maybe more, that can be put down to a passing gravitational wave.
A detection would be confirmed if at least two of the widely separated installations record the same signal. But, as great an achievement as that would be, it really is just the start.
The real aim is to have a new means of studying the Universe - to trace its exotic phenomena in detail in a way that does not rely on light.
"The analogy I like is this: imagine being able to see the world but you are deaf, and then suddenly someone gives you the ability to hear things as well - you get an extra dimension of perception," explains Professor Bernard Schutz from the Albert Einstein Institute and Cardiff University.
"Up until now we've only been able to see the Universe with our telescopes, but with gravitational waves we will be able to hear it as well; and that's going to convey a different type of information.
"Most of the Universe cannot emit electromagnetic waves - we will never see it with light. But we can see it, or parts of it, with gravitational waves."
With this in mind, the scientists have even grander plans which go beyond merely upgrading GEO 600 and Ligo: they want to put an observatory in space.
Preparations for this mission, known as Lisa (Laser Interferometer Space Antenna), are well advanced. It would fire lasers between three spacecraft flying in formation and separated by five million km. Lisa would allow scientists to look at lower frequencies than are possible on Earth, to signals that come from the merger of monster black holes.
Modelling also suggests it should be capable of detecting remnant radiation from the Big Bang itself, enabling science to probe the first moments of creation and perhaps pull together some of its contradictory theories.
"You don't often get things that are very small that are also very massive but, of course, in the very earliest moments of the Universe we did," says Professor Mike Cruise from Birmingham University.
"Some of these observations are going to give us a clue as to how gravity can be viewed in terms of quantum mechanics and the prospect of that is just mind-boggling."
Story from BBC NEWS:
Published: 2005/11/08 20:27:12 GMT
© BBC MMV
The motion of the bodies is relevant because it impacts distance which in turn impacts the strength of a field (read: force of Gravity) which in turn gives us a time lag to measure before a peak field strength is achieved at any given point.
Is that a problem for you?
If that is true, then if the sun suddenly vanished, the earth would continue to rotate in its elliptical orbit for the 8.3 minutes it would take for the gravity wave to disappear. We on this planet would be at the mercy of forces whose originating matter no longer existed, much like looking deep into the cosmos is a journey back through time.
Well, it might be. You see, I was planning on going target shooting Saturday and that would tend to throw off my aim.
Thanks for the ping!
So, what I was asking was this: would the path of light be bent to the same degree as the tube containing that path? Because if yes, then the experiment is guaranteed to bring negative results.
Indeed.
The field is already established and stable. Again, motion within that field is conservative with friction losses. You can't measure the radiative part, it's way too small and you're part of the radiating system. When you are simply moving in a field you are not looking at radiation; you're looking at the gradient of the field.
"which in turn gives us a time lag to measure before a field strength is achieved at any given point."
The distance transversed is a differential in an established gradient, as is the time to the new point at dx where the field already exists. You seem to think that at every new position, the field has to reestablish itself over with communication over the Earth-Moon distance. It doesn't. The force is constant, because it's already established.
The Force the Moon exerts on the Earth is the same as the force the Earth exerts on the Moon. Each object exerts a static field. The pair though radiates a varying field. It's that field that's of interest here.
In a relativistic sense, yes - that is exactly what the theory of general relativity is. What doesn't yet exist is a well-agreed upon unified quantum theory of gravity with electromagnetism. String theory, supersymmetry, etc. are all parts of an attempt to describe these different forces as part of the same "field" in relativistic quantum theory.
GR basically already does this...
Note to all you real physicists: just because I explain it badly doesn't necessarily mean its wrong.
I agree there (or else most physicists would be out of a job...) Scientific matters can't really be settled in the forum of a debate (spoken or written) - there's just too much to them to explain in a short space.
When it was fresh in my mind a Physics Prof at PSU could not punch holes in it, and ended by saying that I had independently derived relativity from another starting point. I respectfully disagreed because it seemed to me that the theory allowed the definition of an absolute zero in each dimension.
Like I said before I can't really be sure what you're getting at from this forum, but it looks to me that you have to be very careful when speaking about reference frames - about 90% of the mistakes I've seen coming from people trying to apply relativity have to do with jumping between reference frames without making the necessary corrections - this is very easy to do accidentally. (Not quite sure what physical statement you're trying to make when you speak of t->0, either...I get the hunch you're trying to use a reference frame with v=c from an external point without properly changing frames, but I can't be sure...)
In any case, if you're just trying to reflect on the nature of relativity, more power to you, but you won't have much luck trying to "reinvent the wheel" - remember that for a new theory to have validity it has to be consistent with current observations and make testable predictions that show the existing paradigm to be inadequate in some realm of application.
Incorrect. The force of Gravity is not constant...it is instead reduced by the square of the distance.
Distance matters.
Nor is the Earth flat...instead it has a vast diameter. This means that when the Moon is on one side of the Earth, there is a shorter distance from the Earth to the Moon from one side of our planet than from the other.
In turn, this means that the Force of Gravity is greater on one side than on the other. This causes tides in our oceans because that change in Force is moving...because the Moon orbits/moves around the Earth.
At no point is the above field or Force constant; distances are changing...and changing distances greatly impact the effect of Gravity.
And because distances change, which cause the Force of Gravity to change on any given point, we can measure (theoritically) the delay between the change in force from that of the correct final value of the force...presuming that the propagation speed of Gravity waves is less than infinite.
The force between the Earth and the Moon is constant. The distance is constant. It's a conservative field. Any point on the surface of the Earth's diameter just cycles back and forth in the conservative field that's already established. There Real bodies involve frictional losses during stress cycling from the tidal forces, so the Moon-Earth distance degrades. That however has nothing to due with the fact that the force between the 2 objects is essentially constant, because the orbital degradation time is eons.
" Nor is the Earth flat...instead it has a vast diameter. This means that when the Moon is on one side of the Earth, there is a shorter distance from the Earth to the Moon from one side of our planet than from the other."
The orbit is calculated by using points to represent the 2 bodies.
High tide occurs twice each day. Here's some graphics:
this one shows the field gradient. The Moon is located at the bottom.
Notice the gradient vectors in the last graphic are constant, not varying.
"This causes tides in our oceans because that change in Force is moving...because the Moon orbits/moves around the Earth."
The Moon and Earth move about their center of mass.
"And because distances change, which cause the Force of Gravity to change on any given point, we can measure (theoritically) the delay between the change in force from that of the correct final value of the force...presuming that the propagation speed of Gravity waves is less than infinite.
The field already permeates the space. It is local and has a constant gradient. Your calculaiton scheme isn't valid, because you assume at every instant of time a new position involves the radiation and correction of a new field from comms between the 2 objects. That's ridiculous. THe spacetime that determines the objects path is already curved locally and the particle representing the objects follows that constant curved path. The moon doesn't move in a straight line and recorrect after comms.
No, the distance is not constant. When the Moon is over Hawaii, it is further away from London. When the Moon is over London, it is further away from Hawaii.
Thus, as the Moon orbits around the Earth, the distance from any one point from the Earth to the Moon changes.
And because the Force of Gravity is determined by distance, this means that the force exerted by the Moon on any given point on the Earth is constantly changing with that change in distance.
That's why we have ocean tides...the Moon's gravitational force is moving along with its orbit.
The moon doesn't have a gravitational force, neither does the Earth.
It did not work out so well for the Enterprise!
So says GR...which is contradicted by Quantum Mechanics and Classical Physics and our daily firsthand observations.
Tides rise and fall twice a day - the rotation of the earth causes tides, not the motion of the moon; in effect the fluid parts of the earth elongate (ever so slightly) along an axis pointing toward the moon due to the pull of gravity between the moon & earth.
Is it possible that the experiment might DISPROVE Einstein, just as Michelson-Morley disproved classical physics?
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