Posted on 02/20/2005 2:18:12 PM PST by LibWhacker
Plans to trace the Moon's orbit with extraordinary new accuracy could reveal kinks in Einstein's theory of gravity and help explain the mysterious accelerating expansion of the universe, says a US researcher.
The acceleration cannot be explained by known forces in the Universe. To account for the behaviour, cosmologists have introduced the concept of a new, as yet unseen, force - dark energy.
But Gia Dvali, of New York University, US, believes there could be another explanation. He thinks the accelerating expansion might be caused by unexpected properties of gravity, which are only seen over very large distances. Taking inspiration from string theory, which proposes the existence of several extra dimensions, Dvali, and NYU colleagues Gregory Gabadadze and Massimo Porrati, suggests that gravity may leak into an extra dimension on this large scale.
"The accelerated universe can be a window of opportunity for understanding the most fundamental aspects of gravitation, and may signal the modification of standard laws of gravity at very large distances," Dvali told an audience at the American Association for the Advancement of Science meeting in Washington DC.
Millimetre accuracy
The scheme to measure the Moon's orbit involves firing a laser beam at mirrors left on the surface by the Apollo 11 astronauts and measuring the time it takes for photons to return. This makes it possible to trace the lunar orbit and, so far, astronomers have used the technique to track it with an accuracy of a few centimetres.
Now, Tom Murphy, Chris Stubbs and Eric Adelberger at the University of Washington in Seattle, plan to use more precise laser equipment to measure the Moon's path to just a few millimetres. At this scale, Dvali's theory predicts that subtle deviations in the Moon's orbit ought to show up.
"If you mess around with gravity, orbits are one of the first things to go," agrees Licia Verde, a theoretical physicist at the University of Pennsylvania. The new experiments have yet to get funding but could take place within the next couple of years.
"One way or another it would be a fantastic result," adds Sean Carroll, at the University of Chicago. But he also warns that there could be other explanations for any deviations in the Moon's path.
Let's hear the "space ping".
Could it be that some particularly repulsive types (insert your 'favorite' names here) repel not only most people but even astronomical objects?
Was it only Apollo 11 that left retroreflective arrays? Seems to me you'd need THREE sets of arrays to positively fix the Moon's position - you'd still have rotations around one and two points...
Great picture of the heaviest particle known to physics: The Moron (it's a bozon.)
In space, no one can hear you ping...
I think all the Apollo missons that landed on the Moon deployed laser reflectors.
Is gravities effect instantaneous?
I think what I am asking is if a gravity sensing instrument points towards the sun is it accurate or is it 15 minutes off (the speed of light).
At last, some common sense.
Re-examining the basic theory.
I just about fell over LMAO when I found the basis for the whole "dark matter" theory.
Astrophysicists using new, nore accurate measuring methods, were able to determine galaxies were rotating (faster or slower) than they should according to Einsteinian models.
So rather than questioning their assumptions, they decided to just create out of thin air, 94% of the universe.
Seriously, the ENU (Expansive, non-decelerative universe) theories need close examining. (Sima, Sukenik, Sukenikov)
I could throw my own name in there because in 94 I came up with the same basic equations.
If we had a good idea of either the average thermal content of space, or the amount of the ZPE, we could come up with very accurate ideas about How old, how big, and how much it weighs.
The sad part about ENU is that the expansion will go on forever, no big crunch in the future, and the density will keep dropping.
Interesting. The 2 Pioneers and 2 Voyagers are also moving slightly faster than expected out of the solar system.
I really love this possibility mentioned in the article: "The accelerated universe can be a window of opportunity for understanding the most fundamental aspects of gravitation . . . " Wow, what's not to love about basic research? (And the Luddites continually carp that NASA didn't even invent Tang, lol!)
Folks have argued that the spacecraft velocities are not due to an error in relativity, but are electrostatic effects.
I don't buy it.
Amen! I've never liked dark energy/matter. Too scary! Though the nine thousand dimensions of string theory are just about as bad! ;-)
An excellent question, actually. See The Speed of Gravity - What the Experiments Say
Given this new theory, does that mean your name will be dropping faster than formerly expected? ;^)
Probably!
;-)
I was surprised when they revised the age estimate, my estimate based on a very rough idea about the average density of the universe was quite close to theirs, ~18.3 billion years.
They have since revised it downward in the 14-15 billion year range.
http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:gr-qc/0010061
Have you ever heard about the "space ping list"? Or did you mention it just for humor?
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