Image: Newton's fixed space vs. Einstein's flexible spacetime, from the film "Testing Einstein's Universe" by Norbert Bartel.
Posted on 04/02/2005 7:01:14 PM PST by PatrickHenry
This year marks the 100th anniversary of a revolution in our notions of space and time.
Before 1905, when Albert Einstein published his theory of special relativity, most people believed that space and time were as Sir Isaac Newton described them back in the 17th century: Space was the fixed, unchanging "stage" upon which the great cosmic drama unfolded, and time was the mysterious, universal "clock in the sky."
Even today, people commonly assume that this intuitive sense of space and time is correct. It's not.
Einstein's 1905 paper, along with another one he published in 1915, painted an entirely different and mind-bending picture. Space itself is constantly being warped and curved by the matter and energy moving within it, and time flows at different rates for different observers. Numerous real-world experiments over the last 100 years indicate that, amazingly, Einstein was right.
But scientists today have reason to think that even Einstein's theory isn't the whole story; another revolution seems inevitable.
The reason for doubt is that Einstein's theory is incompatible with quantum mechanics, another pillar of modern physics that describes the odd world of subatomic particles. When the theories are used together, sometimes, their combined equations produce nonsense. This leads scientists to believe that current theories will eventually be replaced by a single, elegant theory that explains all physical phenomena from the subatomic to the cosmic, the so-called "Theory of Everything."
When will the first shots of this physics revolution ring out? Perhaps when Einstein, like Newton before him, is proven wrong -- or at least not quite right.
To hunt for flaws in Einstein's theories, scientists are crafting experiments that can measure the predictions of relativity with ever-greater precision. One such experiment is NASA's Gravity Probe B (GP-B).
According to Einstein, Earth makes a dimple in the spacetime around it -- something like a bowling ball sitting on a sheet of Spandex. Because Earth spins, this "dimple" is twisted into a shallow vortex. Gravity Probe B is orbiting Earth, right now, in search of these distortions.
Image: Newton's fixed space vs. Einstein's flexible spacetime, from the film "Testing Einstein's Universe" by Norbert Bartel.
GP-B senses the distortion of spacetime around our planet using gyroscopes. (There are four of them onboard the spacecraft.) Francis Everitt, principal investigator for GP-B and a professor at Stanford University, explains:
"Gyroscopes moving through curved spacetime will gradually change their direction of spin (i.e. tilt) with respect to the stars. GP-B will measure that tilting motion with extraordinary precision and from that measurement we can calculate the structure of space near the Earth."
Everitt will give a presentation about Gravity Probe B in April at the "Physics for the Third Millennium: II" conference hosted by NASA's Marshall Space Flight Center in Huntsville, Alabama. The conference is part of the World Year of Physics 2005, a United Nations-endorsed series of events to recognize the 100th anniversary of Einstein's seminal work and to raise public awareness of big issues in modern physics.
In addition to giving a status update on GP-B (in short: so far, so good), Everitt plans to explain how GP-B will measure gamma, an important physics variable used by scientists in their quest to go beyond Einstein's relativity. Roughly speaking, gamma corresponds to the curvature of three-dimensional space.
If Einstein's theory matched reality perfectly, gamma ought to be exactly equal to one. Measuring a value for gamma that's even slightly different from one would be the "first shot" that physicists have been waiting for.
"Gamma is the most sensitive way of measuring any possible deviation from Einstein, because it is sensitive to [any kind of unknown field]," says Thibault Damour, a professor at the Institut des Hautes Etudes Scientifiques, France, and an expert in theories that could replace relativity.
In the GP-B experiment, gamma contributes to the slight tilt of the gyroscopes' spin axes, which are expected to drift about 6.6 arcseconds (0.00183 degrees) during the year-long data-gathering phase of the mission. This drift should allow scientists to measure gamma within about 0.01% of its true value -- and perhaps as good as 0.001%, Everitt says.
If gamma turns out to be slightly less than one, it would support the idea that a new force field exists, akin to gravity but much weaker. Physicists call it a "scalar field." This new field is a feature of some candidate Theories of Everything, including string theory. String theory is popular because of its elegance in explaining all known physical phenomena, from the subatomic to the cosmic. The problem is that string theory is very hard to test in the real world, and no experimental evidence of the unique predictions of string theory has yet been found.
"Finding that gamma is slightly less than one would support the idea of a scalar field, and thus could provide some of the first experimental support for string theory," Thibault says.
If gamma turns out to be slightly greater than one, however, it would be "back to the drawing board" for theorists. No existing theories predict that gamma should be larger than one, so physicists would have no idea how to explain such a finding. "Let's just say that every time I ask theorists what it would mean if gamma were larger than one, they change the subject," laughs Everitt, himself an experimentalist.
GP-B might also find that, within the experiment's limits of precision, gamma is equal to one -- just as Einstein predicted. What would that mean? Perhaps the flaw, if it exists, is smaller than GP-B can sense. Or maybe the revolution's first shots will ring out elsewhere. No one knows.
Gravity Probe B is half-way through its one-year mission. One hundred years down, six months to go. Stay tuned for answers.
The probe is aligned with a star. Any change in the direction of the star in relation to the gyroscopes will be relavistic....caused by bending or curvature of space around the earth.
Is the change in the direction of the star, relative to the gyroscope, due to the bending of the light coming from the star, i.e. the light bends according to the curvature of space?
>But what causes the direction to change?<
See:
http://www.absoluteastronomy.com/encyclopedia/F/Fr/Frame-dragging.htm
Google "relativistic frame dragging" or "Lense-Thirring effect" for more details.....
"Einstein did not prove Newton wrong, he proved him incomplete."
Agreed. If Newtons work had even the tiniest allowance for Lorentz contraction, it would have been complete.
The problem is still Bell's work. He basically proved that there was no hidden variable theory that would reconcile relativity and QM, which was one of the premises of Einstein's EPR work.
And Bell's work seems to start to hint at some sort of universal something, the fact that effects can exceed the speed of light points at a non-relativistic view, a view where there really is a real universal clock.
You got me curious, so I have done some more reading. The best I can figure is that the gyroscope stays exactly the same (that is why they use them).
The axis of the ship will be aligned with a star and left there. If the gyro's axis changes with respect to the ship, it will give them their measurement. It is the ship's axis that will, in reality be changing.
Einstein said that a large object like like a planet would bend light. I think the bending of the light according to the curvature of space is right on the mark.
Thanks for the ping!
Thanks for the insight. Interesting stuff
Thanks for the link. These are new topics to me and very interesting.
I used to spend hours reading this stuff when I was a kid....with the internet around then, we would have never slept!
Begin by pressing the "Pause" button.
Would satellites and random space matter effect the experiment?
Interesting question. I am not qualified to answer it with certainty, but here is a guess: the effect of satellites and random space matter would be so small compared to the effect of the earth, that you only need to consider the earth and can safely ignore the other stuff.
Gee - all they have to do is read 'A Hitch Hiker's Guide to the Galaxy'. They answer is right there - 42.
That would be a better way to go. More dignity.
We all contibute our own dimplette to the fabric of space-time.
It might be put that I am less interested in what men say G-d said then I am in what G-d has done. The results are there to see and the understanding, though hard to manage, is the trip of a lifetime.
Really? How?
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