Quizzes & Puzzles3 mins ago
Gravitational Waves, Einstein’S Ripples In Spacetime, Spotted For First Time
Not a question, but something for anyone who's interested.
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Naomi -- I've been discussing the idea (of, somehow, producing gravity waves by our own means) in a bit more detail with a colleague. My hope was that maybe we'd be able to pump out some numbers by the middle of next week, in terms of what sort of scale we were looking at, ie "can you produce gravitational waves of sufficient size with something humans could feasibly make?" The question of feasibility here will be limited strictly to a mass scale.
It's a nice thought, certainly, to be able to produce and harness gravitational waves ourselves. What for I don't know, but if you can do it then I'm sure a decent use could be found -- one such use might be a very long range message transmitter, as these waves can evidently propagate for billions of light years without losing coherence. But whenever you have to basically blow up a very large star in order to produce something useful I think it's pretty reasonable to doubt that it's likely to happen.
Anyway, if you're still interested -- and if me and my friend get the chance -- then we might attach some numbers to this.
A quick taster, though, from one source I was looking at (see http://
"It appears to be utterly impractical with current technology to detect manmade gravitational waves [my note: this means that production is not in principle impossible, but production at a level worth writing home about is the hard part].. imagine a dumbbell consisting of two 1-ton compact masses with their centers separated by 2 metres and spinning at 1 kHz... one obtains a [gravitational wave] amplitude of 10^-38 [metres]." For comparison, the waves LIGO detected had an amplitude some 100 million million million times stronger. Presumably a future detector might be able to push the threshold of detection down as far as maybe 10^-24, leaving a further 14 orders of magnitude gap to bridge. Good luck with that.
All the same, despite my claim that it is essentially entirely unfeasible to do anything other than observe gravitational waves produced naturally, it would be lovely if I was wrong. I don't think I'll live long enough to find out.
It's a nice thought, certainly, to be able to produce and harness gravitational waves ourselves. What for I don't know, but if you can do it then I'm sure a decent use could be found -- one such use might be a very long range message transmitter, as these waves can evidently propagate for billions of light years without losing coherence. But whenever you have to basically blow up a very large star in order to produce something useful I think it's pretty reasonable to doubt that it's likely to happen.
Anyway, if you're still interested -- and if me and my friend get the chance -- then we might attach some numbers to this.
A quick taster, though, from one source I was looking at (see http://
"It appears to be utterly impractical with current technology to detect manmade gravitational waves [my note: this means that production is not in principle impossible, but production at a level worth writing home about is the hard part].. imagine a dumbbell consisting of two 1-ton compact masses with their centers separated by 2 metres and spinning at 1 kHz... one obtains a [gravitational wave] amplitude of 10^-38 [metres]." For comparison, the waves LIGO detected had an amplitude some 100 million million million times stronger. Presumably a future detector might be able to push the threshold of detection down as far as maybe 10^-24, leaving a further 14 orders of magnitude gap to bridge. Good luck with that.
All the same, despite my claim that it is essentially entirely unfeasible to do anything other than observe gravitational waves produced naturally, it would be lovely if I was wrong. I don't think I'll live long enough to find out.
In a local sense (in vacuum) the speed of light is always constant. The way this changes in General Relativity is that light always travels the shortest path between two points. Again, seems to me that the experimental set-up ensures that if this shortest path changes differently in two places this would also be detected. Hence the "two light beams at right angles" -- if one beam is affected by, say, a gravitational wave front passing through, then the effect on the other beam is not going to be the same in general, and as a result you should still see some variation between the two light beams.
It would be a sick universe indeed to conspire in such a way that such an utterly cool effect that helps advanced our understanding of its nature so profoundly would also be rendered entirely undetectable.
It would be a sick universe indeed to conspire in such a way that such an utterly cool effect that helps advanced our understanding of its nature so profoundly would also be rendered entirely undetectable.
In the end my friend and I decided that the numbers provided by the article I've cited above were enough to satisfy our curiosity about the sort of numbers involved, although that didn't stop us thinking a little about it.
Again the point you have to bear in mind when thinking about this is the sheer incredible weakness of gravity as a force, and that poses a severe practical problem both in studying it and in exploiting it. The event that led to the observation dumped out more energy than is available in the whole of our solar system, so at least to reproduce something of that scale is certainly impossible for us, now and far, far into the future. There's no point in pretending otherwise. At the same time, the comparative ease of using EM radiation to transmit information locally would appear to reduce any incentive to take the idea of a "gravity wave transmitter" seriously enough to develop it further.
But I wanted to finish with a note of optimism. In the first place, despite the apparent lack of scale, if we were able to push sensitivity of gravity wave detectors down further than they are at the moment (and why not?) then that in turn reduces the energy we'd need to create in transmission. The two could conceivably meet in the middle at some point in the future, particularly as at least the concept behind a simple gravity wave transmitter is easy enough -- just spin two heavyish balls around each other really fast and they'll emit gravity waves -- that it's reduced to an (incredibly hard) engineering problem, which may mean that it's solvable given enough time and money.
More to the point, we wondered a little about the idea of a coherent focused gravity wave source -- a "gravity laser", basically. Exactly how this would work is anyone's guess, and it might rely on understanding quantum gravity (which we don't yet) rather than classical General Relativity. But such a device would presumably go some way towards solving the problem of energy demand -- and at the same time probably prove far more useful given its likely coherence over distances measured in millions of light years.
I wouldn't get terribly excited about either approach becoming reality any time soon. But the message I'd really like to put across is that when I call a problem "impossible", I'm not meaning that we should use that as an excuse to stop trying to achieve it -- exactly the opposite in fact. If we only focused on what was possible life would be a lot less interesting.
Again the point you have to bear in mind when thinking about this is the sheer incredible weakness of gravity as a force, and that poses a severe practical problem both in studying it and in exploiting it. The event that led to the observation dumped out more energy than is available in the whole of our solar system, so at least to reproduce something of that scale is certainly impossible for us, now and far, far into the future. There's no point in pretending otherwise. At the same time, the comparative ease of using EM radiation to transmit information locally would appear to reduce any incentive to take the idea of a "gravity wave transmitter" seriously enough to develop it further.
But I wanted to finish with a note of optimism. In the first place, despite the apparent lack of scale, if we were able to push sensitivity of gravity wave detectors down further than they are at the moment (and why not?) then that in turn reduces the energy we'd need to create in transmission. The two could conceivably meet in the middle at some point in the future, particularly as at least the concept behind a simple gravity wave transmitter is easy enough -- just spin two heavyish balls around each other really fast and they'll emit gravity waves -- that it's reduced to an (incredibly hard) engineering problem, which may mean that it's solvable given enough time and money.
More to the point, we wondered a little about the idea of a coherent focused gravity wave source -- a "gravity laser", basically. Exactly how this would work is anyone's guess, and it might rely on understanding quantum gravity (which we don't yet) rather than classical General Relativity. But such a device would presumably go some way towards solving the problem of energy demand -- and at the same time probably prove far more useful given its likely coherence over distances measured in millions of light years.
I wouldn't get terribly excited about either approach becoming reality any time soon. But the message I'd really like to put across is that when I call a problem "impossible", I'm not meaning that we should use that as an excuse to stop trying to achieve it -- exactly the opposite in fact. If we only focused on what was possible life would be a lot less interesting.
Jim, I’m sorry to say this but where science is concerned you do usually come across as a bit of a bubble bursting, glass half empty, sort of chap, so I’m encouraged to see that you added that final sentence to your post. Personally I prefer to cleave towards curiosity, imagination and speculation. The very thought of Star Trek’s (forever impossible?) warp factor speeds excite me. A hundred, a thousand, ten thousand years from now …. who knows?
No I think I would be more positive Jim
You have spent a long time discussing in a rational fashion cutting edge science
and taken a lot of trouble to simplify it to make it comprehensible
It takes time to do this - I have to say I dont bother much as I know some window-licker is gonna say: " whaaaa? "
so instead of simpering and fizzling : who knows Jim who knows ?
I would say well done Jim for spending time telling us punters what it is like in todays cutting edge ivory towers - well done indeed
You have spent a long time discussing in a rational fashion cutting edge science
and taken a lot of trouble to simplify it to make it comprehensible
It takes time to do this - I have to say I dont bother much as I know some window-licker is gonna say: " whaaaa? "
so instead of simpering and fizzling : who knows Jim who knows ?
I would say well done Jim for spending time telling us punters what it is like in todays cutting edge ivory towers - well done indeed
I can appreciate where you are coming from Naomi in general but from my point of view it's because you seem to regard modern scientific status as essentially irrelevant in terms of what the future may hold, whereas I tend to think that future developments in science are more likely to build on what we have now, rather than replace it. I don't know if that's fair or not, and if it isn't I apologise, but it does seem to come across that way. Someone asks a question about science and often our two responses would be something like:
Me: "this is how we currently understand things** (although, subtext, the current understanding is incomplete, but it is still a good starting point for future developments)."
You: "no-one knows."
Both statements are, perhaps, technically correct, but (obviously) I think mine is more useful as an answer. By laying down the current status, it seems to me that this makes speculation about the future easier, at least so long as it's made clear that the present status is not gospel truth, and I don't always do that explicitly. The pointis that it's easier to speculate about where things might go if you know where we are now, what has been tried to push things further, and most importantly of all what has *not* been tried yet.
Anyway, I don't mean to be pessimistic, and for that matter please read the above as a defence of my approach rather than a criticism of yours.
Also, thanks PP for the continuing compliments for my efforts.
**Or, at least, how I currently understand things.
Me: "this is how we currently understand things** (although, subtext, the current understanding is incomplete, but it is still a good starting point for future developments)."
You: "no-one knows."
Both statements are, perhaps, technically correct, but (obviously) I think mine is more useful as an answer. By laying down the current status, it seems to me that this makes speculation about the future easier, at least so long as it's made clear that the present status is not gospel truth, and I don't always do that explicitly. The pointis that it's easier to speculate about where things might go if you know where we are now, what has been tried to push things further, and most importantly of all what has *not* been tried yet.
Anyway, I don't mean to be pessimistic, and for that matter please read the above as a defence of my approach rather than a criticism of yours.
Also, thanks PP for the continuing compliments for my efforts.
**Or, at least, how I currently understand things.
Jim, I don’t mean to criticise – your contributions here are often valuable - but an example of what you write:
//So basically no, to all intents and purposes harnessing gravity waves ourselves is completely impossible and will remain so for long into the future.//
Your conclusion that harnessing gravity waves is ‘completely impossible’ contradicts something I heard from someone highly qualified in this particular subject. You speak with some authority, but you have been known to stop at “impossible”, hence banging the final nail into the coffin of the discussion. However, on this occasion you continued by saying ‘will remain so for long into the future’, rendering the statement entirely inconsistent anyway. All quite confusing.
I actually think the ‘impossible’ judgement discourages people from joining in discussion lest their layman’s ideas be shot down in flames, which is very sad. In my opinion the Science section here is far quieter than it ought to be so I would love to see people exchanging ideas – even if those ideas do seem ‘impossible’ at present. Many an unexpected discovery has been made on the back of ‘impossible’ speculation.
//I tend to think that future developments in science are more likely to build on what we have now, rather than replace it.//
Why? Because you restrict your ideas to what you know? Not me. If I don’t know I’m quite happy to say ‘I don’t know’. I’ve no doubt that many future developments will, as you say, build upon what we have now, but we should never forget that we have been known to be wrong. I think man is on a path to discoveries that currently exist only in the realms of science fiction – and long may we travel it. It’s all so fascinating. Well, I think so anyway. I do hope you take this post in the spirit intended. Onwards! x
Flipping heck! Suddenly I’m rivalling you for lengthy posts! I promise I won’t do it too often. ;o)
//So basically no, to all intents and purposes harnessing gravity waves ourselves is completely impossible and will remain so for long into the future.//
Your conclusion that harnessing gravity waves is ‘completely impossible’ contradicts something I heard from someone highly qualified in this particular subject. You speak with some authority, but you have been known to stop at “impossible”, hence banging the final nail into the coffin of the discussion. However, on this occasion you continued by saying ‘will remain so for long into the future’, rendering the statement entirely inconsistent anyway. All quite confusing.
I actually think the ‘impossible’ judgement discourages people from joining in discussion lest their layman’s ideas be shot down in flames, which is very sad. In my opinion the Science section here is far quieter than it ought to be so I would love to see people exchanging ideas – even if those ideas do seem ‘impossible’ at present. Many an unexpected discovery has been made on the back of ‘impossible’ speculation.
//I tend to think that future developments in science are more likely to build on what we have now, rather than replace it.//
Why? Because you restrict your ideas to what you know? Not me. If I don’t know I’m quite happy to say ‘I don’t know’. I’ve no doubt that many future developments will, as you say, build upon what we have now, but we should never forget that we have been known to be wrong. I think man is on a path to discoveries that currently exist only in the realms of science fiction – and long may we travel it. It’s all so fascinating. Well, I think so anyway. I do hope you take this post in the spirit intended. Onwards! x
Flipping heck! Suddenly I’m rivalling you for lengthy posts! I promise I won’t do it too often. ;o)
I suppose it's just because I prefer to answer by saying what I *do* know, is all. Or, at least, what I think I know, which is obviously a different thing entirely. Hopefully my contributions are mostly informative.
But anyway. On a lighter note, thanks for posting about this and what efforts you do make to try and keep the science board going. It is rather too empty these days.
But anyway. On a lighter note, thanks for posting about this and what efforts you do make to try and keep the science board going. It is rather too empty these days.
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