Gravity waves for dummies
13 Jan 2006 23:12:13 UTC
Topic 190599
(moderation:
I have a few noobie questions here, first what the heck are gravity waves, what causes them, and do they have any physical effect on the areas that the travel through, and if they are found what are the ramifications of that ?
Gravity waves for dummies
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Hey kdog, welcome aboard.
Gravitational wave radiation is caused by something which has mass that is accelerating in its motion (like 2 neutron stars orbiting each other). They do have a physical effect on areas that they travel through. If they are found, one of the ramifications is a picture of the universe that is very clear, compared to images utilizing electromagnetic radiation (e.g., light which can get quite scattered on its way to the observer). A special difference between EM radiation and GW radiation is that, while GWs have a physical effect on 'spacetime', they waves don't get absorbed and re-emitted the way EM radiation does, hence the hope for a very clear picture of where large concentrations of mass are, and not only that, but hopefully indications of what things like neutron stars, pulsars, black holes, etc., look like on the inside, especially during events where they're colliding together, or otherwise merging...
RE: I have a few noobie
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It is difficult to explain this in a few lines. Get any introductory book on general relativity, there are scores of them. My favourite is "The riddle of gravitation" by Peter Bergmann, a coworker of Einstein, but it dates back to 1969 and there have been developments on the experimental side. Maybe Wikipedia can help you but don't take it as a Gospel. Also Scientific American or New Scientist can have good material. See also the LIGO site, it can help you get information, Cheers.
Tullio
RE: RE: I have a few
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Maybe see this link:
http://www.auriga.lnl.infn.it/auriga/grav_wave.html
For a wave to exist you must
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For a wave to exist you must have a system where A causes B to happen nearby and B causes A to happen nearby.
So a wave in a piece of stretched elastic happens because the moving string changes the angle of the elastic, and the change in angle then changes how the elastic moves.
In a water wave the motion up and down alters the height of the wave, and the height of the wave alters the motion up and down.
In a radio wave the change in the E field produces a B field, and the change in the B field produces an E field.
In general relativity there is no gravity. Apples still fall off trees, but not because of some force acting on them, instead the presence of the Earth 'bends' spacetime, and because specetime is 'bent' objects tend to spontaneously accelerate instead of moving with fixed momentum. The 'soundbite' explanation of this is that matter tells spacetime how to bend, and bent spacetime tells matter how to move.
So we have two things that are linkd so that a change in one makes a change in the other which may well make a further change in the first one - as physicists that is all we need to start asking if there will be waves.
Now, remember the radio wave? You need an accelrating charge to create or receive a radio wave, but not to propagate the wave in between.
So too with gravity waves. We expect to transmit them by having a massive accelrating object - a spinning neutorn star will do very nicely thank you - and detect them by the much smaller acceleration they make as measured by the arms of an interferometer.
OK - the equations that link the E and B fields (Maxwell's equations) are lots easier than the equations in GR. The analogy is not as close when written down in maths as it is in English, but it is a reasonably good way of trying to get a feel for what is going on. Hope that helps.
River~~
~~gravywavy
Kdog, You can find some
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Kdog,
You can find some public-level background material on this site, which is linked off the E@H front page. There is also LIGO's page about LIGO, especially the fact sheet. It hasn't been updated for a few years, but the basics are still pretty accurate.
Hope this helps,
Ben