gravitational waves

[glenc (Glen)]

http://www.abc.net.au/news/stories/2...09/2462546.htm
Astronomy boffins from two Australian universities are part of a revolutionary global effort to unlock the secrets of gravitational waves, which could provide a glimpse into the origins of the universe.
The University of Adelaide and the Australian National University (ANU) will take part in a $US200 million project to observe ripples in the curvature of space-time caused by gravity waves.
There is $2.4 million behind the Australian part of the project, in which Australian scientists will be responsible for building parts that will be used to assemble two advanced laser interferometer gravitational-wave observatories (LIGOs) in the United States...

[Hagar (Doug)]

I reasantly attended a presentation on this very subject by one of the Australian scientists/astronomers working on the Australian part of this project. It was interesting to note that the time fluctiations involved in the gravitational wave theory is very, very small. Timing this fluctuation seems to me, the lay observer, almost impossible. The measurement seem to be based on long term measurements in the pulses from pulsars scattered throughout the universe. These very small time fluctuations are to be measured over quite a long period and are expected to be quite small. The extent of the time fluctuation is almost unmeasurable with timing instruments we have here on earth.
Should be interesting to see some of the results they get and how they go about the measurments required.

[astroron (Ron)]

They also have that Satallite with perfectly round balls in space floating around I think in a vacuum, hoping to find Gravity waves.
As far as I know I don't think they have found them yet

[luka]

The current technology is several orders of magnitude short of the required detection precision needed to observe the gravity waves (assuming they exist as predicted by theory).
This is just another media spin to justify spending of such huge amounts of money even though it is know that it won't work.

So don't wait for it, there won't be any discovery any time soon unless we get a supernova going off in our backyard.

[Tommy Camp]

Thats interesting news and good to see Australia involved.
do you have a link further describing the experiments they're planning ?

[Hagar (Doug)]

Here is the CSIRO documents.., http://www.csiro.au/science/ps6a.html

[Tommy Camp]

Cheers for that article Doug.
It cleared it up for me a bit.
Its fascinating stuff hopefully they do prove they exist.

[Sionnagh (Mick)]

Huh? The article makes it sound like Australia is just coming on board with this research.

And if the LIGOs do what they are supposed to do, attention could turn to building a similar observatory somewhere in Australia.

What about the Australian International Gravitational Observatory up the road from here (http://www.gravity.uwa.edu.au/) which is colocated with the Gravity Discovery Centre (http://www.gdc.asn.au/), a public outreach science facility?

I mean, we've been involved in this research for nearly two decades!

;-)
Mick

[astroron (Ron)]

I was wandering when someone would mention that facility?
I have been there.

[Tommy Camp]

Is that what the Gingin facility is for.
I went when i was in primary school but i thought it was a mini particle smasher.
well it is strange then as thats been there a while.
I also want to try there leaning tower they just built there.

[astroron (Ron)]

Tommy, you can try all sorts of gravity experiment's there.

[jungle11 (Greg)]

Hi fellas, another dumb question.

Somebody said these waves would be measured in time fluctuations.
It reminded me of a science fiction book I read where a group of people are in a starship observing a neutron star.
One of them says something like 'this star is ......old but if you were on the surface it would actually be much younger than that because the gravity is so intense it warps? time.

I fully understand that was just a story - but is this feasable in relativity?
I believe it may well be after hearing about the possible effects around black holes.

An amazing universe to be sure.

[jungle11 (Greg)]

Could that effect be why we theorise that time began with the big bang?
When it was infinitely small and massive, no time could have passed at all, so time started rolling only as it expanded. And yet, how could it expand if there was no time for it to do so in the beginning.

Don't worry - no need to answer that, Im just crapping on now and hijacking the thread. Sorry

[Tommy Camp]

Um i think that these gravity waves only affect time in an absolutely tiny way. At least thats what i got from it.
So if you were on the star that was emmiting lots of them then it may indeed be a little bit younger.
but yo'd also be dead so it is a wholly pointless exercise that i would not recommend trying.

[jungle11 (Greg)]

Originally Posted by Tommy Camp

but yo'd also be dead so it is a wholly pointless exercise that i would not recommend trying.

Yes I had realised that believe it or not.

[xelasnave]

Greg siad
One of them says something like 'this star is ......old but if you were on the surface it would actually be much younger than that because the gravity is so intense it warps? time.

What do you think is posible and reasonable first...

alex

[jungle11 (Greg)]

Well alex, surely people have been able to measure this effect with atomic clocks, so I guess the question was a bit premature. I don't know how to calculate the slowing of time say at the suns core, or the core of a neutron star. It would be interesting to know just how much difference there may be in time.
The only article i found yesterday was that this was proven using A.C's on the ground and in a plane - but I thought that proved time/velocity, not time/gravity. But then in relativity mass/velocity is related as well - jeepers, Ive stumbled into the deep end here...

I guess the big bang question would lead me to assume that relativity is flawed somehow
Or perhaps the big bang model is flawed somehow would be more to the point. The way its described pretty much says it came from nothing, not just in time but everything else as well.
That would be my main question on this issue
Seriously, I do not know

[WhiteStarLine (Bill)]

Hi all,

From my recollection after attending a number of free ANU lectures on this, put on by those involved in the project, gravitational waves should be able to be measured even though the displacement is so subtle, we were given the analogy of a 1 kilometre steel girder being displaced by the same distance between an atomic nucleus and its closest electron. The technique involved three earth orbiting spacecraft arranged in a triangle and LIDAR. The satellites are so far apart that even a laser beam spreads out 25 km as it travels from one to another. As the wave advances to the first vehicle, its ripple effect on spacetime is believed to be enough to deflect the beam in a measurable quantity.

To attempt to answer other questions on time slowing down, yes, time slows down close to a high mass object (general relativity) and this is not the same as time differences due to an observer's velocity (special relativity, such as the aircraft experiment in the 1970s). Not only can this be demonstrated, but earth has sufficient mass so that the orbiting cesium and rubidium clocks in the GPS satellite constellation are pre-adjusted to compensate for their distance form the earth's centre. The direction of the adjustment surprised me when I first read it [Danby] as out of interest, I did a Lorentz transformation (inverse of square root of (1 minus v^2 / c^2)) which shows that each second on an object moving at around 4 km per second is around 1.000000000089 earth seconds. However, this special relativity calculation is more than compensated by the slowing down of time nearer the earth's centre due to its mass. This is more complex calculation and I don't know it from memory but as I recall it is calculated using the earth's mass and the equivalent Swartzchild radius (event horizon). Incidentally it is this aspect of GR that Einstein used to explain the precession of the perihelion of the planet Mercury, a well known discrepancy in Newtonian physics.

The reference to the satellite with ball bearings was NASA's Gravity Probe B, which attempted to verify Frame Dragging, another general relativity prediction, where a rotating object that is not perfectly symmetrical can actually drag its own frame with it. Gravity Probe B had precision gyroscopes that attempted to measure this but the ball bearings had been dipped in a coating in a slightly non symmetrical way so after the end of the mission and a number of extensions to adjust the results, no more extensions were granted.

Relativity supplants Newtonian physics calculations for all velocities that are a significant ratio of the speed of light but does not account for quantum dynamics, the first moments of the Big Bang and inside a black hole.

For anyone who is really interested in the practical application of general relativity in today's world, read Ashby's paper on how the GPS constellation has to implement corrections / adjustments to account for almost every GR prediction, plus the Sagnac effect (which is not really relativistic). The paper is heavy, heavy going. It took a dummy like me quite a few days to get through 42 pages. It's at http://relativity.livingreviews.org/...es/lrr-2003-1/.

[jungle11 (Greg)]

Thanks for the answers, very informative - though i doubt id have ANY chance of getting through that paper you talked about!

cheers

[WhiteStarLine (Bill)]

Originally Posted by jungle11

I don't know how to calculate the slowing of time say at the suns core, or the core of a neutron star. It would be interesting to know just how much difference there may be in time.

Out of interest, I just did a calculation on this for my own interest, with more simplifying assumptions than the estimated time of arrival of the Titanic. So here goes:

*********************************** ****************
Andy the Amazing Alien somehow delegated his associates to place coordinated atomic clocks on the surface of a series of widely separated, perfectly spherical, non rotating planets exactly the same size as the earth, Jupiter, the Sun, Sirius B and a neutron star and finally just outside a supermassive black hole. After 50 years, Andy had the clocks retrieved and set up a display for his kids showing the progression of time in each location. Andy's location is on a spaceship so his atomic clock is considered at rest at infinity.




Andy starts his own clock and simultaneously presses the 'replay' button and each atomic clock displays the time it would have shown as Andy's own clock ticked over, second by second. By my rough and untutored and unverified calculations:

• After 1.000 second has elapsed on Andy's atomic clock, the kids glance at the other planetary object's displays. All clocks also show 1.000 seconds except for the neutron star (0.897 seconds) and the black hole (0.500 seconds).
• After 1 hour, the first few clocks seem to be fine but the Sirius B clock has 'lost' a second, the neutron star has 'lost' around 6 minutes and the black hole clock is already 30 minutes behind.
• After 50 years, the earth clock has 'lost' 1.1 seconds, Jupiter has 'lost' 31 seconds, the sun has 'lost' 55 minutes, Sirius B 4.7 days, the neutron star 5.2 years and the black hole 25 years.

Disclaimers / assumptions:

• No aliens strayed any closer than the Swarzchild radius.
• All names fictitious and names of alien children not disclosed.
• The concept of simultaneity means that this experiment could not actually have happened!
• Note that the atomic clocks display 'proper' time in their frame of reference - in other words the atomic clock on Jupiter beats for exactly 50 years as does the one on earth.
• Static mass distribution assumed on each planet.
• Inertial, non rotating, free falling frame assumed.
• Worked Excel spreadsheet available if interested, or to correct my errors.