LIGO, LISA and Gravity Probe B - Gravity Wave Studies

Palomar · 2004-10-11 19:04:18

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.

*Thanks for your input, CM! Interesting, what you say about the Sun's energy budget, energy/gravity -- "but which way the vector points depends on the energy source" --and "nudging gravity at a funny angle out there." Cool!

I'm not quite sure I'm with you regarding your reference to a "passing epicycle"...perhaps you'd please be willing to elaborate that point?

As for Pluto-Charon, perhaps you already are aware of http://www.newmars.com/forums/viewtopic.php?t=1543]New Horizons and New Horizons II?

--Cindy

Shaun Barrett · 2004-10-12 02:35:12

It certainly is very interesting that those distant probes are 'misbehaving'. Their behaviour is at least partially the reason for the Asimov quotation in my signature. As soon as I saw the quote, I imagined the guys at NASA peering at the Pioneer data and saying: "That's funny .."
And, you never know, the tiny discrepancy could be the start of something big in our understanding of what makes space-time tick (excuse the pun).

Hi CM.
Your idea about the energy contained in the solar system, particularly the Sun, is something I'd never considered before. If it were true, though, wouldn't it affect other small bodies in the solar system? Almost all observable natural bodies are much more massive than the Pioneer probes, I realise, but most of them have been tracked orbiting the Sun over many years and any small difference between gravitational theory and practice would surely have been magnified by this repetition and, therefore, easily observed. And wouldn't it be more noticeable in the inner solar system, closer to the main energy supply, than out past Pluto? I've no idea, of course .. just mulling over your hypothesis is all I'm doing.

You referred to the perception that General Relativity holds good for "the scale of the universe at large" but is that necessarily true?
We've had so much trouble explaining why galaxies don't tear themselves apart, rotating as fast at their peripheries as they do, that we've had to come up with mysterious dark matter to supply the extra gravity. Sounds like a 'patch up' job in the physics department to me! :laugh:
Couldn't it be that we really don't know quite as much about gravity as we think we do? And, if so, mightn't this persistent little anomaly with our deep space probes be telling us something very profound?
I'm glad the Europeans are investigating this so thoroughly and I'm hoping for a really historic "That's funny .." moment!

C M Edwards · 2004-10-12 14:32:21

Actually, the remark about the epicycles was put there for perspective, Cindy. Before the days of Kepler, epicycles were used to describe planetary motions in the Ptolemaic model of the universe. Whenever some odd new planetary motion was discovered, it was customary to just slap a new epicycle on the model to account for it.

Now that I think about it, perhaps that's what I was trying to do. :bars:

There is no evidence whatsoever that there's that much angular momentum going unaccounted for in the sun. Trying to put it there is just trying to add an epicycle. In fact, Shaun's post reminds me of yet another epicycle currently in use: invoking dark matter to explain why individual galaxies hold their shapes and groups of them hold together despite inexplicable speeds - this in spite of any other confirming evidence for dark matter.

Dark matter is supposed to hold things together by changing the gravity field and making it stronger at a distance and/or have a shallower gradient than expected. I said that general relativity held good at intergalactic distances, but in reality it doesn't. Not at all. At last count, theorists had to presume nearly 90% of the universe is dark matter in order to force the theory to work. Looked at another way, there's a 90% error in the current theory of gravity.

Dark matter is one big epicycle.

The errors observed in the Pioneer probe's trajectory are small compared to that, but they do appear to have one striking similarity. In both cases, gravity is stronger at a distance than it should be. Only in the case of the Pioneer probe, the difference can't be accounted for by a diffuse halo of surrounding mass, because in order to have enough dark matter in the right place to affect the probe's trajectory you would need enough dark matter in the right place to affect planetary orbits as well.

Dark matter clearly isn't the cause, but I'll bet the Pioneer probe is experiencing the same phenomenon as galactic clusters all the same.

The folks in Europe are on the right track. We don't need another epicycle. We need another Kepler.

Palomar · 2004-10-12 14:49:33

Actually, the remark about the epicycles was put there for perspective, Cindy. Before the days of Kepler, epicycles were used to describe planetary motions in the Ptolemaic model of the universe. Whenever some odd new planetary motion was discovered, it was customary to just slap a new epicycle on the model to account for it.

*Nice explanation; thank you. I don't recall having heard of this prior.

At last count, theorists had to presume nearly 90% of the universe is dark matter in order to force the theory to work. Looked at another way, there's a 90% error in the current theory of gravity.

*Gosh...gravity is such a difficult topic, for me anyway. :-\ Need to continue my "armchair studies." Your comments are so interesting.

The errors observed in the Pioneer probe's trajectory are small compared to that, but they do appear to have one striking similarity. In both cases, gravity is stronger at a distance than it should be. Only in the case of the Pioneer probe, the difference can't be accounted for by a diffuse halo of surrounding mass, because in order to have enough dark matter in the right place to affect the probe's trajectory you would need enough dark matter in the right place to affect planetary orbits as well.
Dark matter clearly isn't the cause, but I'll bet the Pioneer probe is experiencing the same phenomenon as galactic clusters all the same.

*Will definitely keep tabs on this news item. I need to get a bona fide diary! So many wonderful items to keep track of.

I really enjoy your input here, CM.

--Cindy

SpaceNut · 2004-10-12 20:24:21

A comparison of voyager probes might yield simular data for this slowing effect.

Shaun Barrett · 2004-10-14 05:09:25

I've just rediscovered this thread after quite some time and it's occurred to me that my ignorance is still as profound as ever!

Just getting back to LIGO for a while (sorry if this isn't strictly on topic), I understand that two long laser beams, at 90 degrees to each other, split from one laser source originally by a semi-silvered mirror, are re-combined at a sensitive detector to see whether their wave forms are cancelling or reinforcing.
A passing gravity wave will sequentially lengthen and shorten the wavelength of only one of these light beams because the space-time continuum is distorted in only the direction of travel of the gravity wave.
This, it is assumed, will cause the interference of the two laser beams to vary also - causing a variation in the light level measured at the detector.

[Anyone here who is unfamiliar with light wave reinforcement and cancellation would do well to read up on the Young's Slits Experiment - Feynman's use of it in more recent times, many years after its inventor's death, to demonstrate Quantum Entanglement, is particularly spooky! ]

I still don't see why LIGO will work because a gravity wave is indiscriminate in the way it distorts things. Everything is embedded in our 4-space, including the laser light waves lying along the direction taken by the gravity wave. As the gravity wave compresses and then dilates space-time, the LIGO tube and the laser beam within it will compress and dilate in perfect synchrony. Even the human observers' heads will compress and dilate as the gravity wave passes!
The number of light waves per unit length of the LIGO tube (the laser wavelength) will appear unchanged because the actual physical length of the tube will shorten and lengthen as the light waves do, and as the eyeballs of the experimenters do too. If the waves of the re-united beams were re-inforcing peak-to-peak before the gravity wave arrived, they will remain peak-to-peak as the gravity wave passes through also.
This alteration in the length of the tube, or arm, of the LIGO experiment, together with the variation in the wavelength of the laser beam, will be completely undetectable for that reason. It's not a case of the gravity waves being too weak to detect, their influence is universal within our frame of reference and therefore cannot be directly detected .. by definition!

The above is the way I see the situation. But dozens of scientists have spent billions of dollars designing LIGO, so I have to conclude I'm completely incorrect in my reasoning.
Can anyone tell me how you can measure a distortion of space-time (4-space) if you, and every tool you use to measure the distortion, including light, are part of the same space-time being distorted?
???

[You will note I don't try to cast any doubt on the existence of gravity waves. I just don't see how we can ever observe them with an instrument like LIGO.]

C M Edwards · 2004-10-14 05:40:50

Can anyone tell me how you can measure a distortion of space-time (4-space) if you, and every tool you use to measure the distortion, including light, are part of the same space-time being distorted?
???
[You will note I don't try to cast any doubt on the existence of gravity waves. I just don't see how we can ever observe them with an instrument like LIGO.]

The light would distort. As space expanded and contracted in the passing wave, its energy density would change. The surrounding solid objects would distort, too, but not as much. LIGO, in theory, can detect the difference in distortion.

It's an effect analogous to the cosmological redshift. Current theory holds that this effect occurs because space itself is expanding, gradually drawing the energy out of distant starlight after emission. However, the expansion does not dramatically effect solid matter, which is held together under influences much stronger on the local scale. It's like solid matter is shrinking relative to the universe.

So, if the effect is there to be seen at all, LIGO will probably find it.

I don't believe it is, but that's a whole other topic...

Shaun Barrett · 2004-10-14 07:28:33

Hmmm.
Thanks, CM, for the explanation. I'll take it on board and chew it over but, at least for now, I have to say I don't really get it. I know what red-shift is but I'm having trouble relating it to LIGO.
Thinking about space-time like this can do funny things to your head!
Maybe I'll come back in about another 6 months with another angle on it - with everyone's kind indulgence of course.

Meanwhile, I guess we should get back to Gravity-B. (Apologies once more for the slight diversion.)

SpaceNut · 2004-10-18 07:42:28

As we have seen with the deep space probes, an unforseen effect has slowed them. What is it, is this gravity or something new.

The Problem with Gravity: New Mission Would Probe Strange Puzzle

http://space.com/scienceastronomy/myste … 41018.html

SpaceNut · 2004-10-20 11:43:05

Have not heard of much from the probe for the update on proving Einstien's theories but space does warp time around the Earth as indicated by a few satelites. One can only hope that the money spent on the gravity B will prove it as so also.

Einstein's Warped View of Space Confirmed
http://www.space.com/scienceastronomy/w … 41020.html

Palomar · 2004-10-20 11:57:35

Have not heard of much from the probe for the update on proving Einstien's theories but space does warp time around the Earth as indicated by a few satelites. One can only hope that the money spent on the gravity B will prove it as so also.
Einstein's Warped View of Space Confirmed
http://www.space.com/scienceastronomy/w … 41020.html

*This is getting scary, SpaceNut...I was just about to post that same article!

Fascinating stuff. :up: More comments in a later edit...gotta run.

--Cindy

::edit:: "The researchers say their result is 99 percent of the predicted drag, with an error of up to 10 percent. The details will be reported in the Oct. 21 issue of the journal Nature."

Am also enjoying the info relative to black holes. Gas spiraling around a black hole was noted to wobble (precession) like a top. Frame dragging related to spewing of tremendous jets also mentioned. Jet can point in 1 direction for millions of years. Incredible.

P.S.: Image of Earth's "uneven gravity field" -- cool.

RobertDyck · 2004-10-20 13:20:02

*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'm inclined to believe you're right, Cindy. The precession caused by frame dragging that Gravity Probe B will measure is so slight that it took them several decades to invent technology sensitive enough to measure it. This included spheres suspended so that the spacecraft adjusts its orbit so precisely that the spacecraft is hovering around the spheres. The superconductor in the spheres permits measuring their rotation speed and angle without altering its motion. A super-something lead bag that blocks all magnetic fields, so the Earth's magnetic field doesn't affect the spheres. The technologies go on and on. The highly precise orbit has been used for GPS satellites, so there was a spin-off even before Gravity Probe B was launched. But this extreme precision indicates how closely Einstein’s theory of General Relativity works. A conservative scientist would find some other explanation for the anomalies with Pioneer 10 and 11.

The obvious candidate is the heliopause that you mention. The heliopause is an increase in plasma density caused by solar wind pressing against interstellar gas as our solar system speeds through our galaxy. That increased plasma density could cause drag. According to one NASA web site “The last communication from Pioneer 11 was received in November 1995”, so we don’t have any data from its instruments. Is it encountering thicker plasma than expected? I would trust that before jumping to any conclusion about gravity.

Palomar · 2004-10-21 06:39:35

*Thanks for chiming in, Robert. Just that fact that you consider my musings might be correct is a compliment in and of itself.

The heliopause is an increase in plasma density caused by solar wind pressing against interstellar gas as our solar system speeds through our galaxy. That increased plasma density could cause drag. According to one NASA web site “The last communication from Pioneer 11 was received in November 1995”, so we don’t have any data from its instruments. Is it encountering thicker plasma than expected?

*Yep, that's what I've been wondering.

--Cindy

SpaceNut · 2004-10-21 07:54:33

Would we be able to do a radio link up from one of the other probes that are further away from earth or do we believe that they have run out of power for contact with them?

RobertDyck · 2004-10-21 09:20:08

They've run out of power. It might have been possible to transmit on reduced power, but in the end they didn't have enough power to run instruments anyway. http://voyager.jpl.nasa.gov/spacecraft/ … ml]Voyager 1 and 2 are having the same problem; some instruments are turned off to conserve power but all of their plasma instruments are still operational. Voyager and Cassini don't have a reception antenna, so they can't receive anything from Pioneer. Galileo completed its mission by plunging into the atmosphere of Jupiter on September 21, 2003. Only MGS, Odyssey, and Mars Express are equipped with relay antennae. I think all future Mars orbiters will have one, but the Mars Relay antenna is designed for Mars landers, rovers, balloons, or aircraft; not anything in interplanetary space. Co-ordinated activity between craft from different missions is really new.

I think the real answer is to wait for Voyager 1 & 2 to reach the heliopause. They'll get there soon.

SpaceNut · 2004-12-17 05:59:56

Gravity Probe B, the most precise experiment ever, will assess frame-dragging of the fabric of space.

Spinning spheres test relativity's subtlety

Part of this was actually proven a few months back with geo stationary satelites positioning error.
Lengthy article with lots of detail of the how the measurements will be done.
But I am surprized about the silence since the time of its launch. ???

Palomar · 2005-01-25 05:45:25

*SpaceNut, you mentioned wondering -- last week in a different thread -- what might be the latest news about Gravity Probe B. As you indicated in your most recent post here, there -aren't- many updates about it. This just in from spaceweather.com:

SATELLITE ZAPPED: The solar explosion that sparked auroras over Europe also zapped NASA's Gravity Probe B satellite, temporarily causing it to lose track of its guide star, IM Pegasi. Gravity Probe B is no ordinary satellite--it's one of the most exquisite physics experiments ever attempted. Physicists are monitoring gyroscopes inside the spacecraft for wobbles that would indicate a subtle space-time vortex around Earth predicted by Einstein's theory of relativity. Good news: Solar activity has ebbed and Gravity Probe B is back to normal.

Thank goodness, huh? :;):

--Cindy

SpaceNut · 2005-04-06 05:42:11

Well it has been a few months since the last post and still nothing on this very expensive probe of its investigation of Einstein's theory of relativity.

During this time we have heard of geo satelites showing time frame drag around Earth and now we have a new probe concept in the works.

Laser Interferometric Space Antenna (LISA) and the search for elusive gravity waves.
This is a joint ESA-NASA project.
Lots of details in the article.

Palomar · 2005-04-06 05:50:56

Well it has been a few months since the last post and still nothing on this very expensive probe of its investigation of Einstein's theory of relativity.
During this time we have heard of geo satelites showing time frame drag around Earth and now we have a new probe concept in the works.
http://www.spaceflightnow.com/news/n0504/04gravwaves/] Laser Interferometric Space Antenna (LISA) and the search for elusive gravity waves.
This is a joint ESA-NASA project.
Lots of details in the article.

*Yep. A http://www.newmars.com/cgi-bin/ikonboar … 182]thread for LISA was established yesterday.

Let's please keep this thread focused on Gravity Probe B...even if incoming details are scant.

--Cindy

SpaceNut · 2005-04-06 06:02:02

I only mention it since it is still the search for gravity waves and the proving of Einstein's relativity theory not to complicate the threads of discusion.

Palomar · 2005-04-08 06:08:18

*Thanks, Cobra, for deleting the former LISA thread in Unmanned Probes. After re-reading through *this* thread (formerly just "Gravity Probe B"), I was reminded of Shaun's mentioning LIGO in here.

GPB is focused on gravity waves around Earth, whereas LISA will be focused on interstellar gravity waves...then of course there's LIGO.

Thought we might as well combine them into 1 thread...especially as LISA won't be launched until 2012, we get scant reports on GPB and I've not seen much info about LIGO.

And thanks for re-naming this thread.

Here's what I posted in the former LISA thread, pertaining to information about it:

**

I could have sworn I'd posted about this already, and that perhaps a thread had been established. Searching 5 different ways yielded nothing. But this topic -has- come up before, at least once; I posted a reference to it last year.

It's a long and a bit complex article; will opt to copy and paste salient (IMO) points:

Einstein predicted that the motion of large masses should create ripples in spacetime called gravity waves. Now 100 years after his theory, a precise instrument is being prepared that should be able to find out if he was right or not. A joint ESA/NASA mission called LISA (Laser Interferometric Space Antenna) will launch in 2012. It will consist of three spacecraft flying 5 million km apart, which measure their distances from each other precisely. LISA should be able to detect black holes and neutron stars as well as echos from the Big Bang.

Fascinating.

The waves are very weak indeed. They reveal themselves as an alternating stretching and contracting of the distance between test masses which are suspended in a way that allows them to move. If two such test masses were one metre apart, then the gravity waves of the strength currently being sought would change their separation by only 10e-22 of a metre, or one ten thousandth of a millionth of a millionth of a millionth of a metre.
This change in separation is so small that preventing the test masses being disturbed by the gravitational effect of local objects, and the seismic noise or trembling of the Earth itself, is a real problem that limits the sensitivity of the detectors. Since each metre length in the distance between the test masses gives rise separately to the tiny changes being searched for, increasing the length of the separation between the masses gives rise to a greater overall change that could be detected. As a consequence, gravity wave detectors are made as large as possible.

Bit of information about "LISA Pathfinder":

The precision required is 1,000 times more demanding than has ever been achieved in space before and so ESA is preparing a test flight of the laser measurement system in a mission called LISA Pathfinder, due for launch in 2008.

Best of luck on this mission. Am already eager for the data return, LOL.

**

--Cindy

srmeaney · 2005-04-08 07:07:04

Wasn't it just recently, their Australian Partners found major errors in the use of lasers to measure gravity waves? Something about over powerful lasers generating 'noise' in the mirrors and causing real data to be drowned out.

Palomar · 2005-04-08 07:45:59

Wasn't it just recently, their Australian Partners found major errors in the use of lasers to measure gravity waves? Something about over powerful lasers generating 'noise' in the mirrors and causing real data to be drowned out.

*That sounds vaguely familiar, but I couldn't name a specific news source off-hand.

--Cindy

SpaceNut · 2005-04-12 11:24:43

Observing Einstein's Gravitational Waves

The existence of gravitational waves stems from Einstein's postulates. When very massive bodies are disturbed, they radiate waves or ripples that travel through space.
Objects they encounter vibrate without moving, but as a consequence of the deformation of the space-time texture in which they are at rest.

This vibration is akin to how we hear the sound made by a speak in that the electrical wave energy producted by magnetic field defi magnetic oposing forces and gravity to produce a distortion or wave front on the speakers cone that in turn is couple by the air to our ears.

The lasers are setup to sense the wave as it moves between the detectors. Now if gravity has the velocity of light or if it moves slower than time standing still we will not be able to detect any such changes as prodicted. But if it should be between these extremes then possibly someday we will have an answer.

SpaceNut · 2005-05-06 05:39:52

Well here is the latest on the pioneer probes slowing down.
Lost asteroid clue to Pioneer puzzle

FAR-FLUNG asteroids could help reveal the nature of the mysterious force that has nudged NASA's 33-year-old Pioneer 10 spacecraft about 400,000 kilometres off course.

Note that the asteriod in question for affecting the probe has also been effected by the probe it would seem. Gravity the two way street?

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#26 2004-10-11 19:04:18

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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#41 2004-12-17 05:59:56

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#42 2005-01-25 05:45:25

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#43 2005-04-06 05:42:11

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#49 2005-04-12 11:24:43

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

#50 2005-05-06 05:39:52

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

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