There was a lengthy article about this whole "can neutrinos travel faster than the speed of light" debate in this morning's City AM, entitled Why Albert Einstein might have been wrong after all and why this really matters.
I don't get the excitement.
From what I understand, many scientists, including Einstein, assumed that certain forces or particles or waves (light, radio, gravity etc) travel at a certain fixed speed (in a vacuum, relative to the observer etc) and that nothing can travel faster than that. It was inspired guesswork that made Einstein and others agree that the fastest thing of all is photons, which people refer to as "the speed of light" rather than referring to it as "the speed of radio waves" or "the speed of gravity" or anything else (interestingly, they didn't decide for sure whether gravity propagated at the speed of light until 2003, despite common sense saying that it must do).
Now, neutrinos weren't invented, defined, discovered, whatever, until long after it became accepted that the thing which travels fastest is photons, which as Einstein himself acepted, do not travel in straight lines and can be bent by gravity, therefore they can be slowed down, however slightly.
So had Einstein and all his contemporaries known about neutrinos, they might well have decided that the things which travel fastest is neutrinos - because gravity cannot slow them down, heck, not even solid rock can slow them down - and that photons travel a tiniest smidge slower*. All the equations which require people to know the speed at which photons travel (such as the GPS satellites, there are few other practical applications of this knowledge) would then perhaps be the tiniest smidge more accurate, but so what?
If you ask me, the whole thing is about as dramatic as people always assuming that the cheetah is the fastest land-based animal, and that no animal can run faster, but it turning out that there's a little known related species of big cat which can actually run 0.001 mph faster. The far more fundamental points are that (a) "there is a maximum speed at which any animal can run"; and (b) we know roughly what that speed actually is.
* There was an article in a recent Metro saying exactly that - there was a distant super nova or something and the neutrinos therefrom arrived on earth a split second before the photons - but nobody was surprised because the photons had to battle their way out of the gravitational field first, time travelling more slowly in a strong gravitational field, as any fule kno, or else light would be bent away from heavy objects, not towards them.
Wednesday, 5 October 2011
This whole "neutrinos travelling faster then photons" thing
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17 comments:
Photons travel faster than radio waves?
If you ask me, the whole thing is about as dramatic as people always assuming that the cheetah is the fastest land-based animal, and that no animal can run faster, but it turning out that there's a little known related species of big cat which can actually run 0.001 mph faster.
But we wouldn't rule out that there is the possibility of a different cat out there being 0.001mph faster. We don't really know the upper theoretical speed of cats.
Let's think of something more certain: homeopathy doesn't work. We know it doesn't work because it's never been proven to work, and it also breaks a few fundamental laws of physics. Now imagine that it did work. Someone did a double-blind test and we repeated it a few times and it works. The fact that homeopathy worked, and we could all have cheap treatments wouldn't be the most shocking thing. It would be that the law of mass action would be wrong. We couldn't just say "by the way, this doesn't apply to homeopathy", we'd work out why it didn't work for homeopathy and have to change the law.
And with these old laws of physics, lots of other science is based on them because they're considered sound. So, when you find an exception, then as far as people like theoretical physicisists are concerned, all shit breaks loose.
BE, come off it, all these articles refer to "the speed of light" and not "the speed of radio waves", I know about RIVUXY as well as anybody else who did O level physics.
JT, as an arch-cynic, I once tried homoeopathy, assuming that it was a load of nonsense, and to my eternal disappointment... it does work. In a limited and won't-cure-everything fashion, for sure, but it works. It's like technical analysis or land value tax, it works whether you believe in it or not.
From a day-to-day-life perspective, this makes little or no difference, as you point out. And as Joseph says, the reason that it's got the physicists up in arms is that it will mean a lot of work rejigging all the theories which have up to now assumed that the speed of photons in a vacuum is as fast as it gets. They are extremely reluctant to do that and then have some other experimental team come along two years later and say "False alarm, you forgot to allow for X". Hence the caution and the worry among the physicists.
But if is confirmed by a couple of other labs, they will at least fix the theory to match the data. This is miles better than what happens in economics where economists quite blithely ignore the data which conflicts with hallowed neoclassical theoretical precepts like "perfect competition" or "the money multiplier", or "land and capital are the same thing".
Thus leading to the situation where we can design a physical system that beams "Coronation Street" to every house in the land but can't design an economic one that ensures that everyone can afford a house to watch it in.
That article in the metro was cobblers. The supernova was so distant that, scaled up from the Opera experiment, the neutrinos would have arrived days (weeks?, can't find the calculation) before the light if the Opera results held.
And radio waves are just photons with a different energy level compared to light - they're both electromagnetic radiation. Whether they are particles or waves depends on how you measure/detect them.
"..do not travel in straight lines and can be bent by gravity, therefore they can be slowed down, however slightly."
No, but yes. Light can be slowed, depending on the medium it travels through - hence refraction. But according to General Relativity, a 'straight line' through space (a geodesic) is governed by all the mass in the universe. Space is bent, and its the bent path that all particles/radiation follows. So it's this 'bent' path over which velocity is measured.
It's not a question of solid rocks slowing neutrinos, they just pass through without any interaction. Billlions of them pass through your body every second, they stop for neither man nor beast except for *very* rare interactions.
OTOH, those Opera neutrinos were very high energy, much higher than those which came from the supernova. And neutrinos are weird. (But so is the whole of particle physics - there's a good argument that, roughly, says only after they theorize what exists do the fizzicists find it.) Maybe the neutrinos are sufficiently energetic to take a shortcut through the bend of space.
We'll find out when the experiment is reproduced elsewhere, or someone finds the error in Opera. But that's how proper science works, unlike the cargo cult AGW.
Mind you I'm a bit suspicious of advanced mathematics where they have to have all these extra dimensions hiding down the back of the sofa for it all to work.
Okay I can believe/relate to four dimensions, but ten or more?
D: "a lot of work rejigging all the theories which have up to now assumed that the speed of photons in a vacuum is as fast as it gets." Is it that much work? Can't they just type in a different figure for "c" and have done with it? Agreed to the rest of course.
VFTS, the article in Metro said that it seemed unlikely that the recent experiment results were correct, and cited as evidence that supernova thing, which strongly suggested that photons and neutrinos travel at the same speed. And yes I know radio waves are the same as light waves, just lower frequency, I've mentioned that already.
BB, those extra dimensions are a bit advanced for me.
Yes, good contrast to economics pointed out by Derek.
I reckon for a non-physicist the best way to get your head around multiple dimensions is via multiple linear regression in statistics. A scatter plot comparing two variables (e.g. houses prices and house building) in two dimensions is easy to visualize and comprehend. Now just add in variables to test (e.g. mortgage lending, salaries, tax level etc) so you have a space with as many dimensions as there are variables. It is hard to visualise but the maths can handle it quite simply:
Y=A0+A1X1+A2X2+ ...AnXn
Do the analysis to derive a model that describes empirical observed house prices accurately and you have a "house price universe" described by via the necessary number of dimensions.
QP, great minds think alike.
"From what I understand, many scientists, including Einstein, assumed that certain forces or particles or waves (light, radio, gravity etc) travel at a certain fixed speed (in a vacuum, relative to the observer etc) and that nothing can travel faster than that."
No, not really. Particles with a rest mass of greater than zero cannot accelerate to the speed of light. To do so would require infinite energy. Particles (or waves if you prefer) with a rest mass of zero like photons and radio waves "must" travel at the speed of light.
There's nothing particularly there that says that something cannot travel faster than the speed of light. That is something implied from the requirement for infinite energy to accelerate to it.
Finding a particle that does go faster than light doesn't overtuen Einstein: it just reveals special conditions where Einstein didn't think about, in hte same way that Einstein didn't so much overturn Newton as explain bits that Newton hadn't.
The speed of light barrier is only considered to exist not for individual particles or phenomena per se, but rather 'information' (and yes, that is awfully vague). It's to do with causality. Supposedly, if information is able to travel faster than light than it's theoretically possible to see the effects of a thing before it's cause happens.
No we believed " "there is a maximum speed at which any thing can run" and that was known as the speed of light (more technically - speed of light in a perfect vacuum) and that speed is one of the basic constants in the universe used in other formula too (eg the C in E=MC^2). If something is moving faster than that theoretical limit a cascade of physics is wrong. Alternately if these neutrinos are managing it by something like passing through another dimension, or time there is at least the theoretical possibility of dimensional or time travel
Useful opinions on which of these it is, or what other options are possible or even whether a lot of the world's smartest scientists have got their measurements wrong is WAY above my pay grade.
But yes - if what we thought were the basic constants of the universe aren't, even by a tiny amount, it is important
I'd put good money (for reasons I'm privately working on) for the speed of light to be the "maximum" speed.
AC1
Mark, the "speed of light" is actually a physical characteristic of the universe, not just the speed of photons. Einstein didn't just look around for the fastest thing he knew about, like Fahrenheit setting his 0 point at the coldest thing he could lay his hands on. Think instead of a fundamental constant, c, and light (i.e. all radiations) travel at that speed, and mass cannot travel at that speed.
The problem is that velocity in m/s (or furlongs per cock-crow, if you're a units conservative) is a measure that only really works at low velocities. It is better to think of motions as a proportion of c, which is why at higher velocities you have to apply this correction factor. The universe doesn't understand meters per second. It understands proportions of c.
"JT, as an arch-cynic, I once tried homoeopathy, assuming that it was a load of nonsense, and to my eternal disappointment... it does work."
I'd put that down to time, placebo, or spending time talking to someone about your ailment.
It's been tested repeatedly in double-blind trials and it's never done better than placebos.
TW, F, NC, IB, yes thanks for input, if I may sum up my original post: Let us assume that they are right and "c" is a constant but that nuetrinos travel faster than photons, then worst case, the only mistake they made was to define "c" as the speed at which photons travel instead of more correctly defining "c" as the speed at which neutrinos travel.
AC1, best of luck with that.
JT, for sure, placebos often do a very good job as well. Not that I've ever consciously taken them.
"T, for sure, placebos often do a very good job as well. Not that I've ever consciously taken them."
I'm not sure that you have to take anything to get the placebo effect - it's simply persuading your body to repair itself. The "placebo effect" is actually a well documented and powerful medical "treatment", it's just that it's never been studied to any great degree as it's almost impossible to make money from.
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