LIGO

[Dave2002]

https://en.m.wikipedia.org/wiki/LIGO

??? Why can't I put the Title in caps? ???

[ardcarp]

That's technology for you! Gravity waves can be detected from two black holes doing a tango a billion light years away, but capital letters remain one of the universe's mysteries,

Seriously though, if LIGO (wow....done it) really has done this....and it wasn't just a pair of toads mating...then this is one of the scientific achievements of the century.

[french frank]

??? Why can't I put the Title in caps? ???

It's shouting.

Fixed

[Pianorak]

Anyone interested in this subject might find this course of interest. I did it last year and found it fascinating. First-rate content and presentation. https://www.futurelearn.com/courses/gravity

[Pulcinella]

https://en.m.wikipedia.org/wiki/LIGO

??? Why can't I put the Title in caps? ???

It wasn't the capitals or lack of them that concerned me, but the fact that when the message first appeared (without the subsequent question) it looked like one of those email messages occasionally received when someone's account has been hacked.
Just a www link?
Ignore it (and/or delete it).
So I ignored it!

[Daniel]

When first I clicked on this thread it took me to Dave2002's profile! (Obviously I gave a quick gravitational wave and politely retired.)

What astonished/puzzled me and wasn't explained in the article I read, was how they knew the gravitational waves had come from these two colliding black holes. Glancing at the wiki link, I gather it may have sth to do with triangulation, or the fact that it's the only visible event powerful enough to have caused them, but I may have misunderstood.

Anyway it sounds extraordinarily exciting if it turns out to be a new set of eyes on life, the universe etc.

[ardcarp]

There is a grave danger of 'finding what you're looking for'. But I gather that in this case they have been analysing the data since last September...so we can only hope they have got their sums right.

[David-G]

This

https://www.ligo.caltech.edu/page/ligo-gw-interferometer

is an excellent source of information for anyone seriously interested.

It could not have been toads mating, because they have two instruments, one in Washington State and one in Louisiana, and they both picked up the signal, with just the right time difference. I don't think even a LIGO could have picked up the vibrations of toads mating thousands of miles away. Apparently they had to measure a movement of 1/(10 to the power of 19) metres, a tiny fraction of the diameter of a proton. I find it completely astonishing. Re the black holes, I don't think it's a case of "finding what you're looking for". If you are a General Relativitist (or whatever the word is) you can probably calculate what the signal from colliding black holes would look like. Then when you observe that signal, not only have you "seen" the colliding black holes, you have also provided further evidence in support of General Relativity.

I can also recommend this programme on Radio 4:

http://www.bbc.co.uk/programmes/b06zj4dl

which was more informative than I had expected.

[Quarky]

This

https://www.ligo.caltech.edu/page/ligo-gw-interferometer

is an excellent source of information for anyone seriously interested.

It could not have been toads mating, because they have two instruments, one in Washington State and one in Louisiana, and they both picked up the signal, with just the right time difference. I don't think even a LIGO could have picked up the vibrations of toads mating thousands of miles away. Apparently they had to measure a movement of 1/(10 to the power of 19) metres, a tiny fraction of the diameter of a proton. I find it completely astonishing. Re the black holes, I don't think it's a case of "finding what you're looking for". If you are a General Relativitist (or whatever the word is) you can probably calculate what the signal from colliding black holes would look like. Then when you observe that signal, not only have you "seen" the colliding black holes, you have also provided further evidence in support of General Relativity.

I can also recommend this programme on Radio 4:

http://www.bbc.co.uk/programmes/b06zj4dl

which was more informative than I had expected.

Thanks for that.

Reluctantly being drawn into this thread, as I shelved this subject many years ago, I don't find the concept of gravitational waves difficult, it's the nature of gravitation itself which is a little tricky.
For example, it is possible to generate electromagnetic waves by combing one's long hair with a plastic comb, and then shaking the comb vigorously, causing acceleration of the static electricity, and generating electromagnetic waves which are transmitted at the speed of light by reason of maxwell's equations. We can measure thes waves, but can't actually see or feel them.
By analogy, a gravitational disturbance is going to create waves travelling at the speed of light (central to Einstein's theory), rather like ripples in a pond.

But what is gravitiation? As every school boy knows, it's warping of space-time in the vicinity of a massive object - principles of equivalence of acceleration with force of gravity, Fermat's principle of least action, and some fancy matrix algebra on curvilinear surfaces.

But why does mass deform the space time continuum? How does quantum mechanics fit into the picture? At this point, I leave it to Prof. Hawking and the other experts.

[Pabmusic]

...But why does mass deform the space time continuum? How does quantum mechanics fit into the picture? At this point, I leave it to Prof. Hawking and the other experts.

Spacetime is warped by any object (as I sit here typing this I'm warping spacetime - it's just that my effect is so miniscule, no-one notices. The usual analogy is a rubber sheet (a sort of trampoline) upon which you put a large metal ball. The ball bends the sheet, so that a second, smaller, metal ball falls into the depression although it's trying to ravel in a straight line, and it appears 'attracted' to the larger object. Of course, this is all in two dimensions, so you have to imagine something more like an aquarium full of liquid (and that's not to mention the fourth dimension of time!).

Of course it's so much more complex than this really, but it's not a bad illustration.

[Quarky]

Spacetime is warped by any object (as I sit here typing this I'm warping spacetime - it's just that my effect is so miniscule, no-one notices. The usual analogy is a rubber sheet (a sort of trampoline) upon which you put a large metal ball. The ball bends the sheet, so that a second, smaller, metal ball falls into the depression although it's trying to ravel in a straight line, and it appears 'attracted' to the larger object. Of course, this is all in two dimensions, so you have to imagine something more like an aquarium full of liquid (and that's not to mention the fourth dimension of time!).

Of course it's so much more complex than this really, but it's not a bad illustration.

Thank you for that enlightening analogy.

But it does not answer the question of what is in the nature of any massive object ( a rubber ball, myself, or mother earth), which creates this space time warping, and hence an apparent force of Gravity - which Galileo first quantified.

Rather like static electricity - we can trace electric lines of force with iron filings. But what is static electricity? Well it's a collection of free electrons creating a charge. But what is an electron? The last time I looked, nobody seemed quite sure.

[Pabmusic]

...But it does not answer the question of what is in the nature of any massive object ( a rubber ball, myself, or mother earth), which creates this space time warping, and hence an apparent force of Gravity ...

Well, I suppose you'd have to understand the nature of mass (as opposed to weight, that is). It's relative differences in mass that does it, except that you have to remember that, although the Sun has much greater mass than Earth, Earth still affects the Sun (and everything else) to some extent. I have a feeling that the Higgs boson might come in here somehow - but I was always more of a biologist than a physicist.

[Quarky]

I have a feeling that the Higgs boson might come in here somehow -

I guess we are exchanging Gravitons.

Is there an astro physicist or high energy nuclear physicist on these boards who might resolve this issue?

[Pabmusic]

Is there an astro physicist or high energy nuclear physicist on these boards who might resolve this issue?

[Pabmusic]

I do recall that weight is the result of the action of gravity on mass. And that, if we were in a spaceship we'd be able to play ball with a cannonball (because it has no - or very little - weight) but it would still hurt very much if it hit you (because of its mass).