LIGO, LISA and Gravity Probe B - Gravity Wave Studies

Palomar · 2004-04-18 16:49:24

[http://story.news.yahoo.com/news?tmpl=s … avity_dc_1]Click

*Whoa...interesting. I would summarize a bit, but considering the nature of the article I'll do a little snip and paste instead. It'll be launched tomorrow (Monday). Article says this mission has survived axing by Congress seven times. Cost is $700 million:

"NASA is poised to launch a mission 45 years in the making to put a little known tenet of his general relativity theory to its first test.

The Gravity Probe B satellite is the bland name given to one of the most precise scientific instruments ever built...

With four near-perfect spheres -- the roundest objects ever made, according to NASA -- the probe will try to show whether the Earth, which is known to warp both time and space with its mass, also --->twists them like tornado winds as it rotates.<---

'This test of relativity is very simple in concept, but when you get down to the technology of how to do it, it's a testimony to perseverance to say the least,' said Stanford professor Brad Parkinson, who heads the engineering team."

*Here's what especially caught my eye: "Einstein's theory says that --->a small bit of space is actually lost<--- as space is spun around on itself.

'You would find if you could measure the radius and the circumference (of that orbit) there would be a small defect which I like to call the missing inch,' said Francis Everitt..."

If so, where does that "lost space" go?

???

Another item to keep tabs on! Good luck to the mission.

--Cindy

Palomar · 2004-04-19 11:01:50

[http://www.space.com/missionlaunches/la … aunch.html]Countdown!

*Hot off the presses at space.com, including Countdown Clock. They're saying there's a 20% chance the launch might be delayed because of high winds. If delayed, will try again on the 20th.

"The mission has a one-second launch window in order for Gravity Probe B to be properly aligned with its guide star." Um...that's cutting it pretty close. :-\

Includes info about the rocket and the launch site.

Live coverage begins 11:00 a.m. EDT.

--Cindy

Shaun Barrett · 2004-04-20 01:13:33

Hi Cindy!
This is another of those experiments, like the Laser Interferometry Gravity Observatory (LIGO), which purports to prove that gravity warps space. This one tests the warping of space by a massive spinning object (I believe), while LIGO looks for the effect of gravity waves emanating from colossal gravitational events occurring out in the depths of space - such as the collision of two black holes.
I have a lot of trouble visualising how these experiments are supposed to work because, if space/time is being warped by gravity, surely all the measuring instruments being used to measure the distortion will also be distorted in the same way. Those instruments occupy our 4-dimensional space-time continuum, just like the objects they're measuring. If an object distorts, say by shortening an inch, the ruler you use to measure the shrinkage will have shrunk in the same proportion. The net result is that you'll never know the object shrank!
I expressed my concern about this in another thread, specifically aimed at LIGO, but nobody responded. And now I have another quandary to puzzle over with this Gravity Probe B thing!

There must be a perfectly good reason why so many scientists think they'll be able to measure these space distortions but my view is that neither experiment, LIGO or Gravity Probe B, will work.
I know I have to be wrong about this but I don't know why. Can anyone set me straight?
???

C M Edwards · 2004-04-20 06:16:43

Actually, Shaun, I share your opinion about LIGO, and for a similar reason. I have no theoretical reason why it shouldn't work - "gravity waves" seems as good a way as any for gravitational systems to dissipate energy, although they are not required by general relativity as originally derived. However, LIGO isn't an experiment that's been fifty years in the making. It's the culmination of an experimental series that's been _being conducted_ for fifty years. People have been doing experiments like this since the 1960's, and have found nothing except new values for how tiny the gravity waves would have to be to avoid detection.

My prediction about LIGO is: They've found nothing in the previous forty five years. They'll find nothing in the next forty-five.

My next prediction is: Gravity Probe B will find evidence of inertial frame dragging. Gravity can point sideways, just like general relativity says it can.

Unlike gravity waves, inertial frame dragging is already strongly indicated by current observations of astronomical phenomena, including planetary precession and variations in the spectra of accretion disks around black holes. A sideways nudge is the best explanation for some of these observations; i.e., inertial frame dragging. Gravity Probe B will be the first to directly measure this effect using a manmade instrument. It will not provide the first observation in support of inertial frame dragging, just the final confirmation.

As for the "lost inch" and "destroyed space" explanations: they're CRAP, with all capital letters. Inertial frame dragging is a spatial distortion, just like the downward pointing gravity we all know and love. It just happens to be a distortion in a different direction.

Palomar · 2004-04-20 11:13:08

Hi Cindy!

... I have a lot of trouble visualising how these experiments are supposed to work because, if space/time is being warped by gravity, surely all the measuring instruments being used to measure the distortion will also be distorted in the same way. Those instruments occupy our 4-dimensional space-time continuum, just like the objects they're measuring. If an object distorts, say by shortening an inch, the ruler you use to measure the shrinkage will have shrunk in the same proportion. The net result is that you'll never know the object shrank!

*LOL Hi Shaun. The "Post Icon" you used was so appropriate (to my feelings as well, after reading your post).

Um...you raise some very good points (understatement). :-\

I'll have to defer to CM Edwards for some of it (above), who sounds more knowledgeable than I regarding this.

I certainly don't want to sound naive, but...would the gov't spend this kind of $$$, time, etc., it being saved from being axed by the U.S. Congress seven times if it -couldn't- prove something/anything?

I'm hoping for some results, obtainable somehow in ways we might not be aware of. :-\ Getting out of my league here...

They delayed the launch to today. Hopefully this time, and hopefully real results!

--Cindy

C M Edwards · 2004-04-20 11:51:11

I'm hoping for some results, obtainable somehow in ways we might not be aware of. :-\ ...

I'm embarassed to admit I only heard of Gravity Probe B this morning, so I'm no expert...

However, I can guess how it's supposed to work. The component of gravity due to inertial frame dragging is in the same direction as the Earth's rotation. The probe is in a polar orbit, which means that once per orbit it's travelling north relative to the earth and once per orbit it's travelling south relative to the earth. So, when it's travelling north, the inertial frame dragging should appear to be in one direction, and when it's travelling south the inertial frame dragging should appear to be in the other direction. So, the probe will be looking for some miniscule variation with a direction that flip-flops once every orbit. People have seen what they believe to be inertial frame dragging in celestial mechanics, and the general consensus is that the evidence so far is pretty solid, but that flip-flop effect is the one thing you can't get just watching Mercury's orbital precession.

Well, that's how I'd do it if I had a Gravity Probe... :;):

The outcome of this experiment could be important to Humanity's future as a spacefaring species. If inertial frame dragging as described by Einstein is real, it means that spacetime can conceivably be manipulated arbitrarily using energy in forms that we can control. If inertial frame dragging is possible, so is warp drive. It's just a matter of degree and density.

Shaun Barrett · 2004-04-20 23:09:04

Thanks for the sympathetic reply, Cindy. Yeah, the look on that icon's face does occasionally match my own when discussing Einstein's stuff!

And thanks, CM, for your input here. It sure is good to hear that someone else finds the LIGO experiment unlikely to succeed. At least if my opinion on it is shown to be flawed, I won't be alone in my embarrassment.
And thanks for the description of the Gravity Probe B experiment. If it's as you say, then yes I think I can see it working and giving us a result. Your clarification of it is much appreciated.

SBird · 2004-04-21 01:07:32

CM Edwards - I've got to respectfully disagree regarding LIGO. The fact that the instrument hasn't seen anything yet is not suprising, the noise level they can get is just not low enough to spot gravity waves unless they happen to catch the gravity waves from something like a pair of black holes merging. In order for LIGO to work, it's really got to be in space. We know that the gravity wave phenomenon exists from observation of binary neutron stars where the slow decreasing their orbital rotation rate around each other is nicely explained by energy lst by the generation of gravity waves.

The bit about 'lost space' is pretty bogus though. It's not really being lost, it's being dragged around the Earth and therefore the spacetime path travelled by the probe deviates from what one would expect.

Here is a link to the Gravity Probe B website [http://einstein.stanford.edu/]here! Take a gander at the 'what is gp-b'/'story of gp-b' link for an excellent description of how the instrument works, what it's measuring and how it was built.

For example, those 4 gyroscopes have a maximum devation from being a perfect sphere by less than 20 nm - that's equivalent to the Earth having a maximum height feature of 16 feet.

I stumbled across the gp-b website about 5-6 years ago and have been following it off and on since. It's nice to finally see it up in orbit.

Palomar · 2004-04-21 10:39:34

*You all seem in agreement that the "lost space"/"losing an inch of space" thing is baloney. (And I'm in no position to argue otherwise)

I'm still wondering about this, however: "...the probe will try to show whether the Earth, which is known to warp both time and space with its mass, also twists them like tornado winds as it rotates."

What about the "twisted tornado winds" effect? If it's discovered to be so, what sort of impact will that discovery have on these theories and etc.? What is the significance (especially related to -time-), and why important to determine?

--Cindy

C M Edwards · 2004-04-21 13:40:42

"Twisting them like tornado winds"... If only!

Actually, if antimatter power and spin drive ever become realities, and if we can ever manufacture our own miniature Hawking-style black holes (hmm... Did I forget any "ifs"? ), then we might someday be capable of producing enough power in a dense enough package to make a gravitational field do just that. However, the entire planet Earth does not. The sideways component of gravity in Earth orbit due to inertial frame dragging is infinitesimal.

SBird, I'll say again that I have no reason LIGO shouldn't work. But saying it has to be done in space because of the noise here on Earth just puts another maximum limit on the effect. There's still an absence of evidence.

If LIGO doesn't work, it would be safe to start asking where all that neutron star energy is really going.

SBird · 2004-04-24 01:16:10

ecrasez - the gravity 'tornado' effect was predicted by general relativity and figured out by a couple of researchers about 2 years after Einstein published his theory. We're expecting to see the effect. If it's not there, it'll be very big news. However, that's not expected.

The whole 'missing space' thing is just a poor interpretation of what's going on. My understanding is basically that as the satellite orbits the Earth, the Earth is slowly dragging the fabric of spacetime around it. As a result, the satellite's actual path ends up being slightly skewed. The gyroscopes can detect this deviation which is VERY small.

Really, in some ways gravity probe B is very boring - it's expected to find what's already been predicted and nothing else. The operation of the probe and the precision it had to be made to, however, is anything but boring. It's by far and away the most impressive piece of engineering I've every seen. It's 4 nearly perfectly smooth spheres spinning inside a solid quartz starfinder scope bathed in liquid helium in a superconducting lead balloon.

CM - If you're going for absolute evidence, I agree. OTOH, there's very good evidence that gravity waves exist. Relativity gives predictions for what the energy in gravity waves should be (with error bars, of course). The rotational slowdown of those neutron stars is right smack dab where it should be if gravity waves are the cause. If LIGO were detecting gravity waves, something would be wrong - it's too noisy to be able to detect them. In theory, LIGO should pick something up but potential signals are just getting lost in the seismic noise of the Earth. However, LIGO's shortcomings don't in any way invalidate the exitence of gravity waves. The true test is a space-based interferometer which should be able to detect the waves.

Further - if gravity waves don't exist, relativity has to be wrong. If you posit that (which is a valid point, relativity could have flaws in it), there's no reason to think that gravitational frame shifting is any more likely to be observed than gravity waves.

Palomar · 2004-04-24 13:42:27

Really, in some ways gravity probe B is very boring - it's expected to find what's already been predicted and nothing else. The operation of the probe and the precision it had to be made to, however, is anything but boring. It's by far and away the most impressive piece of engineering I've every seen. It's 4 nearly perfectly smooth spheres spinning inside a solid quartz starfinder scope bathed in liquid helium in a superconducting lead balloon.

*Hmmmm....well, for some of us laypeople, this stuff is rather exciting "overall." But I see your point.

What amazes me especially is how anyone figures out how to design such a probe in the first place, to test these sorts of theory/theories. If it were up to me, we'd be lucky to be pedaling bicycles... It's "wow" to me, how people figure out inventions -- like this probe.

--Cindy

Palomar · 2004-04-30 06:30:05

*I anticipated this thread would lay dormant for a while. Then the folks at Astropix posted http://antwrp.gsfc.nasa.gov/apod/ap040428.html]this item for April 28th.

This is the first actual "inside look" at this contraption I've had. :;): I didn't expect it to look quite like that...

By the way, everything is running smoothly in the mission so far.

--Cindy

Shaun Barrett · 2004-04-30 07:24:39

My first "inside look", too. Thanks, Cindy!

SBird · 2004-05-04 09:50:11

Cool, the view you posted looks like a view of one of the quartz gyroscopes. (two of the gyroscopes are quartz, the other two are silicon to make sure that any peculiarities inherent to one material don't cause problems. Either Scientific American or SCience had a nice cutaway diagram this month of the whole probe. Imagine a big, pear-shaped balloon with a fat stick running most of the length down the center from the skinny end and that's what gravity probe B looks like.

The big pear is the lead jacket that contains all of the liquid helium. At those temperatures, lead superconducts and therefore blocks out almost all of the Earth's magneic fields and stray electromagnetic signals. The 'stick' is the actual workings of the probe.

There's a long tube that lets light in and supports the rest of the assembly in the middle of the liquid helium reservoir. After the spacer tube, there's the star scope. This was made of big blocks of solid, ultra pure quartz. No glue was used, the pieces were machined to super close tolerance and cleaned so well that they just atomically fused together when they were assembled so the entire star scope is one big piece of solid quartz. This eliminates differential movements due to heating or cooling. The star tracker zeros in on that guide star and tracks it with incredible precision. There's some sort of trick with wobbling the probe back and forth to get the star to move so that the accuracy is high enough. The guide star is also being tracked from the ground since any movement it makes will actually throw off the probe!

Finally, at the end of the 'stick', there's the 4 gyroscopes which are electrostatically suspended and spun up with gasseous helium to peroper speed. A coating of chromium on the gyroscopes generates a tiny magnetic field which can be read by a superconducting quantum interference junction, allowing tracking of the motion of the spheres.

Palomar · 2004-05-06 10:43:36

Cool, the view you posted looks like a view of one of the quartz gyroscopes. (two of the gyroscopes are quartz, the other two are silicon to make sure that any peculiarities inherent to one material don't cause problems. Either Scientific American or SCience had a nice cutaway diagram this month of the whole probe. Imagine a big, pear-shaped balloon with a fat stick running most of the length down the center from the skinny end and that's what gravity probe B looks like.
... The guide star is also being tracked from the ground since any movement it makes will actually throw off the probe!

*Thanks, SBird, for the descriptions. I'm hoping perhaps you can remember which periodical/magazine that was? I looked for a cutaway of the probe on Google. I found 1 tiny illustration (which wasn't a cutaway or diagram) in a .PDF format. One other .PDF as well, but it was totally professional scientific jargon --

I'm also wondering how all the debris floating around "up there" might effect the probe. Hopefully nothing will hit it. :-\

--Cindy

SBird · 2004-05-06 10:58:57

Sorry, I just moved and so all my stuff is still largely in boxes. If I find the latest Science and Sci Am, I'll check. In the meantime, check out this http://einstein.stanford.edu/]link. Go to the 'what is gp-b' then 'story of gp-b' and check out page 4. The diagram isn't as good as what I saw but still gives a good rundown. The whole 'story of gp-b' link is the best resource for getting info on GP-B. It gets a bit technical at points but is well written.

Incidentally, I found out that Gravity Probe A was launched back in 1976.

Palomar · 2004-06-21 15:49:19

*SBird: I checked your link and info regarding Gravity Probe A shortly after your post. I could have sworn I responded to your post... :-\

Here's an http://www.universetoday.com/am/publish … 004]update on Gravity Probe B

"...is about halfway through the initialization and checkout phase of its mission. Mission operators have transmitted more than 5,000 commands to the spacecraft, and everything seems to be functioning properly, including its gyroscopes and the targeting system that keeps it locked onto the guide star: IM Pegasi. If everything continues to go as planned, it should begin scientific operations in August, and deliver the final results in a year."

IM Pegasi? Why that particular star, I wonder? :hm:

--Cindy

Palomar · 2004-08-02 16:10:41

http://www.spaceref.com/news/viewpr.htm … 26]Revving up Probe B's gyroscopes

*Haven't seen an update on this in a while. Everything's functioning well. Gyros #2 and 4 are spinning at greater than 4800 rpm (contrasted to 90 rpm for gyros #1 and 3)...which makes me wonder what's "full-speed"?

"Each full-speed spin-up takes most of a day. Helium gas is flowed over the gyro for 90 seconds, and tests are run to ensure that the helium usage rate for that gyro corresponds to previous measurements. If all measurements check out, the full-speed spin-up, in which helium gas is flowed over the rotors for 2-3 hours, commences."

::shakes head:: That's amazing. Glad to read the mission is going okay.

--Cindy

Palomar · 2004-09-03 12:48:52

http://www.universetoday.com/am/publish … 392004]The going got tough

*Latest update:

"Controllers expected to get the spacecraft orienting on its target star within a few days, but it took weeks because sunlight reflecting off of dust particles confused its tracking system. Engineers also had to tweak the spacecraft's software to compensate for cosmic rays that flashed into its telescope."

*Apparently that's been fixed.

"First, sunlight reflecting off floating dust particles confused the satellite's star-tracking sensors. These sensors use the locations of constellations to orient the spacecraft, and the tiny shining specs looked like stars. The dust eventually cleared, but then another problem arose: Cosmic radiation in the form of high-speed protons peppered the telescope's light sensor, causing false signals. Mission scientists had to tweak the satellite's software to ignore these pulses. And on it went like this for weeks; scientists would solve one problem only to encounter another.

'Now it has become very routine, and we only take about a minute to acquire the star as we come up over the horizon,' Everitt says. (The satellite loses sight of the guide star during each orbit because it passes behind the Earth, so it must reacquire the star as it comes back into sight.)..."

*They were also concerned about the possibility of dirt having gotten into the gyro housings, but that fear was put to rest -- all is okay in that respect as well.

All the little nuisance work must have been exasperating, to say the least. :-\

--Cindy

SBird · 2004-09-03 13:53:08

Incidentally, yesterday, Gravity Probe B entered into the science collection phase. The only remaining hitch is a persistent unknown force that's causing the liquid helium to circulate more than anticipated. The movement is under the limits of the experiment but just barely.

SpaceNut · 2004-09-03 13:56:22

Great update for I had not seen or heard of much from this experiment to prove or disprove Eistines theories.

SpaceNut · 2004-10-11 14:04:26

Are we seeing the effect of space time curvature by the long ago launched probe from the pioneer series?

Two slowing probes baffling scientists
Pioneer 10, 11 in far reaches of space
http://www.pasadenastarnews.com/Stories....00.html

Palomar · 2004-10-11 14:53:38

Are we seeing the effect of space time curvature by the long ago launched probe from the pioneer series?
Two slowing probes baffling scientists
Pioneer 10, 11 in far reaches of space
http://www.pasadenastarnews.com/Stories … ...00.html

*Yes, I saw an item related to this a few weeks ago; IIRC, the matter was part of an article (related topic) in a different thread. This especially caught my attention from the article SpaceNut posted:

"For the most part, that interest in the space community has blossomed in Europe more than in the U.S., he said.

In the five months between May and September, Europe has hosted three meetings related to the Pioneer anomaly, with a large one in Bremen, Germany, completely devoted to the problem in May.

The other JPL proposing researcher, John Anderson, said European interest in the problem is historically motivated. "There's always been a strong interest in gravity in Europe,' he said.

This mission would fall into that category because there is some thought that a unifying theory such as string theory, that would bring together gravity and the three other forces of nature, could help explain the anomaly, Anderson said.

Turyshev said part of the reason the U.S. seems less interested in such a mission is the focus on the Vision for Space Exploration..."

*I wish some of the brainiacs who used to frequent this board would drop by and chime in again, at least occasionally! Oh well.

--Cindy

P.S.: "For unknown reasons, the Pioneer 10 and 11 missions NASA launched in the early 1970s have traveled slower in the far reaches of the solar system than scientists expected...Thee most logical explanation would be an unaccounted-for systematic source, such as a gas leak from the propulsion system."

*Well, they are the scientists, not I, but I wonder if the nearing of the heliopause and bow shock out there has anything to do with this slowing down. :hm:

I started this thread and we have precious little updates about Gravity Probe B; since we're still discussing
gravity, I don't care if we go off-topic a bit.

C M Edwards · 2004-10-11 15:49:39

*I wish some of the brainiacs who used to frequent this board would drop by and chime in again, at least occasionally! Oh well.
--Cindy

Be careful what you wish for. :;):

P.S.: "For unknown reasons, the Pioneer 10 and 11 missions NASA launched in the early 1970s have traveled slower in the far reaches of the solar system than scientists expected...Thee most logical explanation would be an unaccounted-for systematic source, such as a gas leak from the propulsion system."
*Well, they are the scientists, not I, but I wonder if the nearing of the heliopause and bow shock out there has anything to do with this slowing down. :hm:

The idea that the propulsion systems on both probes malfunctioned is hokum. Even if it could conceivably have gone out in the same fashion on both probes at once, they haven't lost enough fuel to execute the maneuver.

No, something unexpected is retarding their progress.

If they were still travelling at their original speeds, I'd say the idea of drag from the heliopause was ridiculous, too. However, these probes are only travelling at a few kilometers per second. It's become relatively easy to nudge their course compared to how they behaved in the inner solar system. I don't think it's that, though. This is a cumulative effect; this anomalous force has been acting on the probes for a long time, probably since before they cleared the solar system.

I think it's either a problem with our idea of gravity or a problem with our idea of what energy is actually available in our solar system and its neighborhood, and my guess is the latter. I can't see why General Relativity would work on both our local scale and the scale of the universe at large but not just outside Pluto's orbit. However, I could see how some vast error in accounting for the sun's energy budget would do that. Energy creates gravity, but which way the vector points depends on the energy source. Maybe there's some aspect of the Sun's structure that we don't know about, or haven't accounted for because it doesn't match the tiny trickle we see on its surface, that is nudging gravity at a funny angle out there at Pioneer 10.

Then again, maybe Pioneer 10 has become snagged by a passing epicycle. There's no telling at this point.

If NASA won't get off of it and send a probe to check this out, ESA needs to. I've always wanted to see Pluto and Charon. This anomaly is just one more good excuse.

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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Re: LIGO, LISA and Gravity Probe B - Gravity Wave Studies

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