Date: August 8, 2011
Title: Luminiferous Aether
Podcaster: Jim Bell
Organization: Sounds of Science
Link: www.soundsofscience.co.uk
Description: Jim Bell and Dr Martin Austwick talk through the concept of the luminiferous aether and the famous Michelson and Morley experiment that was designed to detect this mysterious light-propagating medium. The podcast is framed around a song written by Martin paying tribute Michelson and Morley and one of science’s most famous failed experiments.
Bio: Jim is a freelance science communicator based in Bristol. He works as a presenter delivering science shows in schools, writing and producing podcasts; most notably he is the co-host of the Geek Pop Podcast and has been a part of the Geek Pop Festival since 2008. He also has an unhealthy obsession with Tarantulas. Find him on twitter @jimothybell.
Sponsor: This episode of “365 Days of Astronomy” is sponsored by — NO ONE. We still need sponsors for many days in 2011, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this web page, or contact us at signup@365daysofastronomy.org.
Transcript:
Hello and welcome everybody to a very special edition of the geek pop podcast made especially for 365 days of astronomy. My name’s Jim and I’ve been speaking to Dr. Martin Austwick a physicist and musician, who’s written a song all about the luminiferous aether. To find out what that is and what it has to do with Astronomy, keep listening…
My name’s Martin Zaltz-Austwick. I work as a lecturer at the Centre for Advanced Spatial Analysis at UCL, University College, London. So at the minute I’m a social physicist, but before that I was a medical physicist and before that I was a quantum physicist so my background is in physics. I started playing songs about science a few years ago in about 2007. So I’d write the songs and perform them at various nights in London. For things like Robin Ince’s School for Gifted Children, Geek Pop, London Word Festival, Latitude Festival, things like this. Put out an album called Songs from the Scientific Cabaret which has all those songs about scientific things…
Luminiferous aether
Luminiferous aether
Light is a wave, travelling through the empty space like ripples on a pond
But, if that is the case, then what is the water that light is the ripple on?
That’s the luminiferous aether
Luminiferous aether
There’s a beautiful analogy in the first verse of the song about light travelling through space like ripples on a pond. As a humble biologist who is no expert in physics at all, I’ve always found it hard as a concept to see how light could travel as wave and then how it would travel through a vacuum.
From quantum physics, we also know that light can behave as a particle, in more like a particle way. But I’m going to put them aside I’m going to talk about the things that the Victorians knew which was that light certainly does act like a wave in a number of circumstances. And they understood that because they’d done a series of experiments, what they saw was interference patterns and diffraction patters and those sorts of things that you only see if light was a wave. If light was just a particle you wouldn’t see those sorts of behaviour. Victorians created this analogy of light like ripples on a pond because most waves, as it says in the song, have a propagation medium. Like sound waves propagated in air, water waves propagated in water, and so the question was what does light propagate on? The result of the Michelson-Morley experiment, which I talk about later in the song, was that it doesn’t exactly work that way. It’s easier to think about what light is, and in classical terms, non-quantum physics, light is more like a force, made of electromagnetic fields. And what that means is a force field, so like you know when you do the experiment with a bar magnet and you put a piece of paper on the top, and you put some iron filings on the paper and you get a nice pattern and that’s caused by a magnetic force field. And that force field doesn’t need a medium to propagate in it’s just an extension of the bar magnet in space. It exists in space so it doesn’t need a medium to propagate that force. The difference with light is that it’s an oscillating force field so it’s not a bar magnet that stays the same – it move up and down and backwards and forwards. And once you about light being a force you don’t need any medium of propagation.
As the Earth revolves around the sun we must plough this luminiferous ocean
There must be some kind of way for detecting how the water tends to push against the forward bow
If you look at waves approaching from the direction that you’re going
They’ll appear to get here faster than those coming from behind
So Michelson and Morley built an interferometer to
Detect these kinds of differences
Hoping they would find…
Also, the machine that Michelson and Morley brought was the interferometer which sounds like a complicated word. How exactly do they work and are they still useful for astronomers and other physicists?
They are very useful, I mean the way that they work is that they use this wave nature of light. Interferometers usually have two arms. These split a beam of light. They go down one arm and come back and then the other arm and come back, and then the two beams meet back up again. And the idea is that if the beams are exactly the same length, the oscillations of the light – the peaks and the troughs – will match up when they meet again. And so when they meet again they recombine and you get a strong signal. They had this interferometer with two arms perpendicular. I won’t go into all the details of the experiment but basically they were looking for an effect of the Earth moving through this luminiferous aether. They said that in the direction that it’s moving, the light waves will get compressed a little bit; and if the light waves get compressed once they’ve gone through one of the arms of the interferometer and they meet up again it will damp out the signal. They didn’t see anything – that was the exciting thing. That sound like it shouldn’t be very exciting but it was very surprising that they didn’t see any of this effect. Interferometers, to turn to your other question, interferometers are use a lot in things like medical physics – because they’re very accurate, you can see incredibly small difference in length and speed using this sort of technique. I remember actually, I heard about this experiment they’re planning and I don’t remember the details of it which is a bit embarrassing but the basic idea is to have three satellites in the solar system at really, really, large distances, again I can’t remember the exact details but we’re talking about millions and millions of kilometres, I guess. And they will use this to detect gravitational waves. It’s the same idea where you have a triangle of satellites and if there’s any disturbances to the waves of light because of gravitational waves coming then you’ll see a change in the interference pattern. So that’s a very large scale interferometer.
I think I’m right in saying that gravitational waves are predicted by Einstein’s relativity theories…
Yes, I think it’s part of general relativity, it’s been a long time since I studied it but I don’t think I could solve the equations for you now…
Luminiferous aether
Luminiferous Aether
Luminiferous aether
Luminiferous Aether
But they didn’t find it at all because it didn’t exist…
Also, It’s often thought of as a great, failed, experiment…
People didn’t know that before and it’s really counter-intuitive. I mean if there were a real luminiferous aether, a sea that light rippled on, then you can’t imagine that being the case. And knowing that the speed of light is constant in all, with certain provisos, in all frames of reference, was really surprising. Einstein took that and came up with this theory that has very surprising and counter-intuitive results. Many of which have been tested, but without that knowledge in the first place from the Michelson-Morley experiment he would never have been able to do that.
It’s amazing really to think, apparently Michelson won a Nobel prize in 1907, I guess he wasn’t viewed as too much of a failure…
No, but it was a really good experiment! It’s a classic bit of physics in that it was really well planned, it was a very well designed experiment if you read about it, and they did that stuff really well. They quantified their errors – they said well, if the speed of light does change, it only changes by this much. Each iteration of this experiment got more sophisticated, I think there was a version where they had the interferometer mounted on a heavy block of metal so the vibration wouldn’t transfer. And that was sat on a bed of mercury just to make absolutely sure there were no errors creeping into the experiment. So they did these really good experiments to absolutely put this to bed. Because without that all of the relativity, special and general, would kind of fall apart so they were really important experiments.
Absolutely crucial, and without that knowledge then we wouldn’t have astronomy or any of the stuff up in space as we do today.
Well it would look very different astronomy, I think.
Definitely. Well thank you very much for talking to us Martin. It’s a beautiful song and I hope everyone listening is enjoying it as well.
Thank you very much.
We hope you’ve enjoyed this podcast, brought to you from Geek Pop. If you’d like a little bit more science and music then check out the Geek Pop podcast at www.geekpop.co.uk If you’d like to hear a little bit more of Martin’s music, for free, then head over to his website which is thesoundoftheladies.com. Thank you very much for listening everybody.
End of podcast:
365 Days of Astronomy
=====================
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.