Double Pulsar Discovered

Nothing new... by BiOFH · 2004-01-09 19:34 · Score: 4, Funny

John Goodman's ass has been emitting gravity waves for years.

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- I am made of meat.

Re:Nothing new... by BiOFH · 2004-01-09 21:28 · Score: 3, Funny

Oh. Poor thing. If moderation is so bad, then why are you so worried about messing up your karma?

Coward. :)

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- I am made of meat.

Speed of Gravity by fejikso · 2004-01-09 19:37 · Score: 5, Interesting

Does someone know if these waves travel at the speed of light? Of course, as predicted by the theory.

I suppose so... otherwise we could eventually devise faster-than-light communications, and I don't think the Universe is that nice :)

Re:Speed of Gravity by UPAAntilles · 2004-01-09 19:51 · Score: 5, Insightful

The answer is a resounding...we dunno!

We have determined that it is at least 2x10^8 m/s, however, it may be as much as 3.6x10^8 (faster than light). We honestly don't know. I'm pretty sure I heard my quantum mecanics professor at the University of Arizona mention something about Einstein's theories requiring light and gravity to equal in speed, but I'm an aerospace engineer, not a quantum physicist. If they do equal...if the sun were to disappear, we would see the light of the sun and still be fine orbit wise for about 8 minutes. Kinda funny to think about.

As for the faster-than-light communications, we could do that with tangled photons. Einstein was troubled by the fact that quantum entanglment causes an instantaneous change across a large distance. It's been used in a large number of sci-fi novels, including Orson Scott Cards Ender's Game series of books.
Re:Speed of Gravity by DigiShaman · 2004-01-09 20:10 · Score: 5, Interesting

This was discussed in a NOVA special about String Theory in The Elegant Universe. You can watch all three hours of the program online for free. I think the part about the speed of gravity (as to if it's effect are instant or at the speed of light) are in the first hour of the program. Check it out here

http://www.pbs.org/wgbh/nova/elegant/program.htm l

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Life is not for the lazy.
Re:Speed of Gravity by sahrss · 2004-01-09 20:49 · Score: 5, Informative

You can also download the entire thing if you like. I just spent 15 minutes digging all this up, figured I might save someone else that time.
Some previous Slashdotters showed us how (first link is to the highest quality download).

I got it to work fine with this (remove the spaces!):
curl "http://a768.g.akamai.net/5/768/142/3f9e9589/1a1a1 afb6ae049ae214fc034aad839a91985ea187bea5786f362d84 1a61948bf2688f01f87fb6fdf0e7ceb61c22186fb/nova_eu_ 30[12-14]c[01-08]_mp4_300.mov" -o universe#1_#2.mov
Re:Speed of Gravity by TexVex · 2004-01-09 21:09 · Score: 5, Informative

When calculating the orbits of celestial bodies, it is necessary to assume that gravity is instantaneous. When an object moves, its gravity appears to move with it instantly. The earth appears to orbit the Sun's present position rather than where the sun appears to be due to speed-of-light delay.

As I understand it, though, there are two ways to look at it. The Earth is approximately 8 light-minutes from the Sun. The Earth is either orbiting the Sun's actual position, or it's orbiting a point that would be about eight minutes in front of the Sun's extrapolated path based on its position and momentum at that given instant.

It comes down to a question of whether or not gravity is a field or a particle. If it's a particle, then it must travel at some unimaginable speed. If it's a field then it would share some of the properties (like velocity and direction) of the object that generates it, and changes to the field would propagate outward from the object at the speed of light. These changes to an object's field of gravity are thought to produce "gravity waves" that have yet to be detected.

I could very well be muddled on this subject but I have done some reading on it. Please correct me if I'm wrong.

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Fun with Anagarams! LADS HOST, SHALT DOS. HAS DOLTS. AD SLOTHS, HATS SOLD. ASS HO, LTD.
Re:Speed of Gravity by spiro_killglance · 2004-01-09 21:24 · Score: 4, Interesting

No, entanglement is strange. Entanglement is
non-local, that is it isn't a property of a
single particle, its a property of a collection
of particles. You can't use entanglement to
send information faster than light, because you
can't use entanglement to send information at all.
What you can do is use entanglement to had extra
information to a classical communication channel.
If you add to a channel transmitting n-bits of
information, n entanglement pairs of particles one
part of each pair at the reciever and one at the
transmitter, then you can send 2^n bits of information which is fanastic. But without the
classical channel you can't send anything at all,
so dispite being non-local, entanglement evades
brakeing the rule that you can't communicate faster than light.
Re:Speed of Gravity by TexVex · 2004-01-09 21:37 · Score: 4, Interesting

The Earth is either orbiting the Sun's actual position, or it's orbiting a point that would be about eight minutes in front of the Sun's extrapolated path based on its position and momentum at that given instant.
What I meant to say here is "or it's orbiting a point that would be the Sun's extrapolated position based on constant motion from its position, direction, and velocity about eight minutes ago." That point won't be exactly where the Sun is now but it will be pretty close.

That's what I get for trying to discuss something I'm familiar with but not extremely knowledgeable of at 3:30 in the morning.

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Fun with Anagarams! LADS HOST, SHALT DOS. HAS DOLTS. AD SLOTHS, HATS SOLD. ASS HO, LTD.
Re:Speed of Gravity by akruppa · 2004-01-10 02:38 · Score: 4, Interesting

As for the faster-than-light communications, we could do that with tangled photons. Einstein was troubled by the fact that quantum entanglment causes an instantaneous change across a large distance. It's been used in a large number of sci-fi novels, including Orson Scott Cards Ender's Game series of books.

The problem with quantum teleportation is that you need to send classical information in order for the receiver to reconstruct the quantum state to be transmitted.

When Alice prepared her entangled quantum bit with \phi, the state that is to be transferred, Bob's (entangled) quantum bit is in a superposition of states that do not yet reveal any information on what \phi was. Alice needs to measure her \phi and entangled qubit and send that info to Bob, who can then apply some operators on this copy of the entagled qubit and that puts it into the state that \phi originally was in. So the speed of quantum teleportation is actually tied to the speed of classical information transfer, thus limited to the speed of light.

Alex

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Heisenberg may have been here
Re:Speed of Gravity by Effexor · 2004-01-10 04:23 · Score: 4, Informative

Yes, it is a rather confusing analogy. The way to look at it is that the sheet is space itself. Draw lines on it, and each of these is a straight line. Now when you place the object in it and it curves the sheet, notice that the 'straight' lines are now curved by it. This is analogous to the mass warping space. The lines are now curved, and the 'straight' path of an object on this curved space is now going to curve as well.

Now imagine it in 3D.

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As the air to a bird or the sea to a fish, so is contempt to the contemptible -W.B.

Question for a physicist by MillionthMonkey · 2004-01-09 19:39 · Score: 5, Funny

I wonder how many times these two neutron stars could bounce if they were to hit the water at an angle of 20 degrees.

detecting gravitational waves? by UPAAntilles · 2004-01-09 19:42 · Score: 3, Interesting

I would be very suprised if they could actually "prove" the existance of such waves. Gravity is such a weak force compared to the other three (strong, weak, and electromagnetic) that pulsars light-years upon light-years away would be washed out by the gravitational effects of, well, the rest of the universe! There's been conjecture about this for years, and entire theories to try and resolve this problem of no detection (several string theories have been developed around this problem) We've even built miles long observation "tools" (like this one in Livingston, LA). However, if we can solve the background noise radiation, and the pulsars are close enough to earth, and have a large enough gravity, they just might do it! Einstein's theory of general relativity states that two orbiting stars (two orbiting anythings, but stars have a lot of mass and therefore gravity, so it would be pronounced) will 'shed' some of their momentum through gravity waves. The detection of these waves could revolutionize physics! It would allow us to determine the existance of the graviton, and if we ever did that, the world as we know it would change. Because once we pin it down, we can start converting energy to it, and probably start research on a feasible "anti-graviton" of sorts. Warp Drives, here we come! (well, not likely, but a guy can hope)

Re:detecting gravitational waves? by MillionthMonkey · 2004-01-09 20:15 · Score: 3, Insightful

The detection of these waves could revolutionize physics! It would allow us to determine the existance of the graviton, and if we ever did that, the world as we know it would change. Because once we pin it down, we can start converting energy to it, and probably start research on a feasible "anti-graviton" of sorts. Warp Drives, here we come! (well, not likely, but a guy can hope)

What are you talking about? There is no such thing as an "anti-graviton" since the graviton is its own antiparticle, like the photon is. And how would detection of a gravitational wave help advance technology as opposed to pure science? Pure gravity research is not exactly known for its technological applications.

And it isn't obvious how we will start "converting energy" into gravitons once we've succeeded in "determining their existence". Except in a trivial sense, like when you push a rock up a hill. But you can do that now.
Re:detecting gravitational waves? by rokzy · 2004-01-09 21:05 · Score: 5, Funny

I hate it when physics topics come up on slashdot, there are always annoying people like you who know a few words but don't really have a clue.

you're the science equivalent of the guy who says his OS is AOL.
Re:detecting gravitational waves? by kwpulliam · 2004-01-09 22:46 · Score: 4, Interesting

"And how would detection of a gravitational wave help advance technology as opposed to pure science?" Well...you generally need the science for the technology. "Pure gravity research is not exactly known for its technological applications" Hmmm. Pure electrical research was useless for centuries, but it's QUITE handy nowadays... I think I'm gonna go turn up the thermostat. Don't prejudge unknown applications. Your grandkids may not comprehend how we lived without it. I'm sure glad I don't have to chop wood, read by kerosene, drive a horse or steam cart, or write this out longhand to a discussion journal and wait 3 months to see it in print.

Seems to make sense.. by Darken_Everseek · 2004-01-09 19:42 · Score: 4, Insightful

Just on an intuitive level, at least. Gravity is a lot like electro-magnetism, in that it produces it's effects invisibly. That, to me at least, implies some method of energy transfer. Waves seem a reasonable enough explanation. I wonder though, if the same wave/particle duality will be observed as we see in photons. Cool stuff.

At last?? by talonx · 2004-01-09 19:46 · Score: 4, Informative

Gravitational waves have always been notoriously difficult to detect (infact near nigh impossible) because of their weak nature. This looks like a good opportunity to do that.

How fast is gravity? by DAldredge · 2004-01-09 19:46 · Score: 4, Insightful

How fast is gravity?

If the sun went poof, how long would it take for Earth to go off into space? 8 minutes or as soon as it happened?

Yes by rebelcool · 2004-01-09 19:46 · Score: 5, Informative

Article

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Re:5p33d 0f gr4v17y by Deraj+DeZine · 2004-01-09 19:46 · Score: 3, Funny

I think you might be confused: Moore's Law applies to the speed of computers, not their size.

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True story.

G Waves and other fun things to look for by DumbSwede · 2004-01-09 20:02 · Score: 3, Informative

This is great scientific news, I would imagine astronomical observations should allow for accurate predictions of resultant gravity wave phenomenon. By knowing the time and amplitude of the gravity waves emanating, one should be able to calibrate and adust LIGO to a great deal of precision. I think till know we have been in a I-Duh-Know-Maybe-It's-Working state. Once we know LIGO is working, we will be able to finally detect gravitational phenomenon directly.

As an aside, with a system this unique, and not to sound too much like a loon, but perhaps we should look for an ET presence. Not as the creators, but there maybe unique physical process than can be exploited in such a system, and doing so may give off a detectable technological signature.

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Letter To Iran

Actually not yet, but... by UPAAntilles · 2004-01-09 20:12 · Score: 5, Informative

Here's a cool kid's site that has some animations

It's for the LISA (Laser Interferometer Space Antenna). Space.com did a story on it a little while back, and it was in a Scientific American, but I'm not sure which, I have too many lying around. Unfortunantly, it doesn't launch until 2009.

Gravity doesn't pull, but rather pushes. by DigiShaman · 2004-01-09 20:18 · Score: 3, Interesting

I've always belived that our concept of gravity is wrong. I think the reason our universe is expanding is not because of "dark energy", but because space is trying to displace a minority substance called matter.

Imagine if you will that the earth is a bubble in water. The more dense a planet is (or the higher the air pressure is in a bubble), the more effort it takes for space to want to displace that matter. But, what if we could control the "pressure". In other words, what if we could spoof a matter in the form of energy in front of a space craft? Rather then the ship propelling itself through space, you could instead have space push the craft much like the difference in water pressure wants to push an air bubble to the surface.

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Life is not for the lazy.

Actually you wouldn't notice by DumbSwede · 2004-01-09 20:19 · Score: 3, Interesting

I think most scientists believe the Sun's gravity will lag at the same speed as light.

BUT, assume the Sun winked out while it was night for you.

You wouldn't feel a thing.
No massive, "Oh, MY GOD we're lurching into space!" That's the whole point of space curved by gravity, you can't tell that you're not traveling a straight line. The weather would goto hell in a handbasket fast from no incoming heat after a few minutes or hours, and of course dawn wouldn't come. There might be some tectonic activity, some isolated magnitude seven and eights here and there, but most likely not immediately.

No you wouldn't even notice at first as the night hung on forever, and Earth continued on a straight line into the blackness...

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Letter To Iran

Re:Actually you wouldn't notice by bhima · 2004-01-09 21:32 · Score: 4, Interesting

Actually this was the topic of an old Sci-Fi short story called "A Pail of Air". Basically it was a thought experiment starting with the nemesis theory (Giant dark proto-sun in a highly elliptical orbit which swings by every epoch to cause mass extinctions).
So Nemesis swings by and strips the Earth off the sun's orbit. The goes dark and cold and there is some tectonic activity. The interesting thing is that the Earth's temperature starts to drop to match the temperature of open space. The oceans freeze and the atmosphere condenses and rains down to the surface, where it forms strata based on what temperature the gas condenses at. To the protagonist goes out side and digs past the CO2 until he finds a strata of O2 and brings a pail of air inside.
But I doubt even a small number of people could survive this for long!

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Nothing in the world is more dangerous than sincere ignorance and conscientious stupidity.

Nobel prize for pulsar discovery by etymxris · 2004-01-09 20:33 · Score: 5, Interesting

Anybody know why Jocelyn Bell received no credit for actually discovering pulsars, yet her thesis advisor, who actually seemed to do nothing, did?

Indirect detection by Beryllium+Sphere(tm) · 2004-01-09 21:01 · Score: 4, Interesting

If the system is emitting gravity waves then it's losing energy by doing so, and the orbit will gradually decay.

You can measure the orbit precisely when there's a pulsar in the system, which is a good timing source. Then you can check whether the orbit's decaying at the rate predicted by the math of gravity wave radiation.

That measurement's been done for another binary system. See http://astrosun2.astro.cornell.edu/academics/cours es//astro201/psr1913.htm and read about 3/4 of the way down.

Observation agrees with Einstein in this case.

Maybe Not. by Anonymous Coward · 2004-01-09 21:03 · Score: 5, Interesting

Article 1, Article 2.

Some scientists that have inspected the calculations believe the experiment is flawed and that they instead measured the speed of light itself (ie: they probably measured the speed of the light they were using to make their observations with, not the speed of the Jupiter distortion).

Correct answer: The speed of gravity is not (yet) a scientifically proved and universally accepted fact. Saying anything else is bad science.

In 85 million years, "wioll haven be" by NoData · 2004-01-09 22:26 · Score: 3, Interesting

In the university press release:
The stars will coalesce in only approximately 85 million years, sending a ripple of gravity waves across the Universe

So...wait, 85 million years from when? Now? Or is it 85 million years from what we currently observe, which is probably several million years in the past (neither link provides the distance of the pulsars from earth)?
In other words, will we observe the coalescing in 85 million years, or 85 million + time of transit?

Sheesh, it never occurred to me how dicey verb tense is in astronomy...Talking about the future of distant objects that exist in the past which we are observing presently.. Reminds me of Dr. Streetmentioner's Time Traveler's Handbook of 1001 Tense Formations from Restaurant at the End of the Universe.

Animations by allrong · 2004-01-09 23:35 · Score: 3, Interesting

Animations of the evolution and current state of the pulsar system are available.

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What is the inverse of the Matrix?

gravity wave detection by simonharvey · 2004-01-09 23:40 · Score: 3, Informative

there are at least two methods that I know off that can be used to detect the sign of gravity waves:

The first is to photograph the upper atmosphere with an incredibly sensitive camera during night time, the reason is that gravity waves (that have a period of a few hours) cause the upper atmosphere to strech and compress causing the atoms that cause air glow to seporate into layers. this shows up on the image as bands. these gravity waves are emitted from the center of the earth.
the second is to use an incredibly precise receiver tuned to a reliable transmitter in the HF bands, to a frequency that gets reflected by the ionosphere. since gravity waves will cause the ionosphere to expand and contract the change in velocity will cause the HF signal to be doppler shifted, meaning the gravity wave will be shown up in a slight variation of the incomming frequency.

the second option can be done by ham radio operators (if they really know there stuff), the first option is for universities since only they have the budget to buy the expensive equipment.

simon

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