Einstein was right (+/- 0.05%)

Mahray
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Topic 191832

Einstein at least 99.95% right

Basically it looks like Einstein's General Theory of Relativity is right, the problem being with the measurements (hence the 0.05% error rate). The article is written for an interested but not science postgrad person.

Mike Hewson
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Einstein was right (+/- 0.05%)

Quote:

Einstein at least 99.95% right

Basically it looks like Einstein's General Theory of Relativity is right, the problem being with the measurements (hence the 0.05% error rate). The article is written for an interested but not science postgrad person.


What can I say? That just rocks!! :-)
Excerpts:

Quote:


...... two highly compact neutron stars, each of which weighs more than our own Sun but measures only about 20 kilometres across.

The two stars whirl around each other at a million kilometres an hour, emitting lighthouse-like beams of radio waves.


Quote:


...... when one pulsar passes behind the other, its signal travels through the warped space-time created by the one in the foreground.

Using Einstein's theory, the researchers calculated that this warping would add a 90 microsecond delay to the arrival of the signal on Earth, which is just what their measurements found.


Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Mike Hewson
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I've found the source paper

I've found the source paper in Science and wheedled out the info. Here's the plot with the money shot...

The red curve is predicted, the data in black with error bars is the measurement. Residuals ( vertical axis ) refers to the time delay after all other things have been accounted for. This leaves the 'Shapiro delay' that refers to the passage of light across the intervening space between the pulsars as described. The horizontal axis is orbital phase, for this purpose 90 degrees is essentially when one pulsar ( closer to us ) is near-occulting the signal of the other ( further from us ) - hence the delay peaks to near 90 microseconds as the rear pulsar's signal ( whose delay is being measured ) shoots across that highly GR distorted space on it's way to us.
Wow!! That's luvelly!! :-)
Cheers, Mike.

( edit ) On the ready-reckoner value of the speed of light being one (1) Imperial foot per nanosecond ( ten to the power of minus 9 ), then 90 microseconds ( ten to the power of minus 6 ) translates to 90,000 feet 'worth' of delay! This roughly means the 'extra' distance to travel due to GR warping, comparing to flat Euclidean space. That's about 17 miles!! What a neighbourhood....

( edit ) Joseph Taylor ( physicist, Princeton ) is quoted "They're tightening constraints on any alternative to Einstein's theory"

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Andreas
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Joseph Taylor and Russell

Joseph Taylor and Russell Hulse discovered the binary pulsar PSR1913+16 in 1974, and found that their orbits do shrink just as predicted, with a smaller than 0.5% margin of error.

http://nobelprize.org/nobel_prizes/physics/laureates/1993/illpres/discovery.html

Click my stat image to go to the BOINC Synergy Team site!

Mahray
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RE: I've found the source

Message 45935 in response to message 45933

Quote:
I've found the source paper in Science and wheedled out the info. Here's the plot with the money shot...

Thanks for doing the hard yards Mike, that really does look good :)

Mike Hewson
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RE: Thanks for doing the

Message 45936 in response to message 45935

Quote:
Thanks for doing the hard yards Mike, that really does look good :)


Thanks for pointing it out!
( I've got online subscriptions for Science and Scientific American, so let me know anytime in the future .... )
It does look good indeed. The data ( in black ) is accumulated from many orbits ( 100+ ), and the exact shape of the predicted behaviour ( in red ) is sensitive to whichever theory of gravity you want to test. It's from the stats analysis on the curve/data fit which yield a confidence of 0.99987 +/- 0.00050 to Einstein's GR. Whew!
If you can imagine the plot being repeated many many times along the horizontal axis, because it represents a cyclic event, you can envision the delay stretching in and out as the pulsars orbit. It seems to be significant when the pulsars are within about 30-45 degrees either side of aligned ( from our viewpoint ). Stretch the space, let it relax, stretch the space, let it relax ..... you get the idea :-)
Of course the whole space between the pulsars is pretty warped, but this study has isolated the 'traverse' ( as in surveying ) along our line of sight that cuts the system. Thus it's trimmed a few dimensions out, but heck I can't visualise beyond three anyhows ... :-)
Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Chipper Q
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I appreciate your extra

I appreciate your extra effort too, thanks Mike.

Does the chart also show the degree of gravitational lensing of the foreground star on the signal from the background star? Or is that one of the things accounted for before measuring the 'Shapiro delay'? Or is it the degree of lensing itself which determines the delay?

Mike Hewson
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RE: I appreciate your extra

Message 45938 in response to message 45937

Quote:

I appreciate your extra effort too, thanks Mike.

Does the chart also show the degree of gravitational lensing of the foreground star on the signal from the background star? Or is that one of the things accounted for before measuring the 'Shapiro delay'? Or is it the degree of lensing itself which determines the delay?

I'm not sure 'lensing' is the right term, as no image is being formed, but you've grasped the idea that gravity is altering the spacetime so that the radiation emitted from the rear pulsar is being distorted by it's passage past the companion star when the alignment ( to hit us ) is right. Hence the delay.

Imagine a really long piece of string, as long as one Imperial foot per nanosecond of transit time, and held tight between the rear pulsar one end with one of the radio dishes at Parkes [AUS], Jodrell Bank[UK] or Green Bank[USA] at the other. So when the second pulsar ( which is a neutron star of course ) goes in front then you have to pay out the string only to wind it in later - all because of the spacetime distortion. That would be on top of a lot of other motions of course. It's a sloppy analogy, but one way to visualise it.

I'll mention that there were three other parameters measured and compared to GR expected values, which were accurate to within about one percent, so not as good as the Shapiro number. These were

(i) the derivative of the orbital period [GR accurate to 0.5%] - a negative number, so the period is getting shorter, meaning they orbit each other more rapidly as time goes on;

(ii) the gravitational redshift parameter [GR accurate to 1.2%], which indicates the decrease in frequency/energy of the radiation as it 'climbs out' of the system;

(iii) a Shapiro 'range' parameter [GR accurate to 1.5%] which when combined with the 'shape' parameter [in a fairly compicated way] models the delay due to the other pulsar's gravity well. It was the shape parameter which was quoted as having that high concordance with GR.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Chipper Q
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Thanks, Mike. Regarding

Thanks, Mike. Regarding lensing, I didn't mean to imply that the observation was made at (or even remotely close to) the focal point. But it seems like the signal received from the background star constitutes an image that was also blurred (diffracted?) by an amount proportional to the red curve on the chart. I was trying to picture the warped spacetime as being analogous to a couple marbles on a stretched rubber sheet. So when the light from the background star is passing closer to the foreground star, the increasing curvature in the sheet results in lensing of the signal, whereby redshift parameter and Shapiro delay are gleaned. If it's not proper to think of the signal as having been lensed, how should I regard or describe it?

Mike Hewson
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RE: Thanks, Mike.

Message 45940 in response to message 45939

Quote:
Thanks, Mike. Regarding lensing, I didn't mean to imply that the observation was made at (or even remotely close to) the focal point. But it seems like the signal received from the background star constitutes an image that was also blurred (diffracted?) by an amount proportional to the red curve on the chart. I was trying to picture the warped spacetime as being analogous to a couple marbles on a stretched rubber sheet. So when the light from the background star is passing closer to the foreground star, the increasing curvature in the sheet results in lensing of the signal, whereby redshift parameter and Shapiro delay are gleaned. If it's not proper to think of the signal as having been lensed, how should I regard or describe it?


Naw, 'lensing' is fine, I like 'diffracted' too, and 'blurred' is tres cool .... I suppose if we had radio dishes for eyes we'd be saying stuff like that .... :-)

Mind you, then we'd be wondering what Neutrino Man was looking at when he came around for pizza & a beer ..... :-)

You're understanding is right on, but it's hard to get the right language isn't it? Maybe 'warping' and 'curvature' is best .. dunno ?

Being such a foreign circumstance ( it doesn't happen hereabouts ) the visualising is difficult too. Rubber sheets give the flavour for sure though.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Chipper Q
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RE: You're understanding is

Quote:
You're understanding is right on, but it's hard to get the right language isn't it? Maybe 'warping' and 'curvature' is best .. dunno ?

Yeah... when I think of light diffracting through a glass lens, the photons at different frequencies will be diffracted by different amounts (as with a prism). But the photons in the light that's curved around a star by the warped spacetime don't separate into their individual colors, right? They're all curved by the same amount, regardless of frequency? So then 'warp' and 'curve' are probably best. Thanks, Mike :)

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