Double Pulsar Discovered

jabberjaw writes "Nature is reporting that a set of two pulsars could be emitting gravitational waves. Einstein predicted the existence of gravitational waves in his general theory of relativity, but a gravitational wave has yet to be detected. Find out more about gravitational waves and pulsars at Eric Weisstein's World of Physics."

Comments

Speed of Gravity

[fejikso]

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

[DigiShaman]

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

Re:Speed of Gravity

[spiro_killglance]

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

[TexVex]

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.

Re:Speed of Gravity

[akruppa]

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

Nobel prize for pulsar discovery

[etymxris]

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

[Beryllium Sphere(tm)]

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.

[Anonymous Coward]

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.

Re:Actually you wouldn't notice

[bhima]

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!

Re:detecting gravitational waves?

[kwpulliam]

"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.