Do we understand light?

[flobadob]

Last month during a test at the LHC some neutrinos apparently travelled faster than light. This as we all know has been proven to be impossible. So do we really understand all of the properties of light, and if not what are the possibilities?

[Slapshot]

Stick with the standard model........it's not confirmed that a scientific breakthrough has been found or that the Neutrinos went faster than light therefore any feasible hypothesis is little more than WAGing

[rojash]

... but even if they did, it wouldn't show that we don't understand the properties of light, but that we have a problem in our assumption that nothing can travel faster than light.

[jake-the-peg]

The fascinating thing about this experiment is that it is begining to look as if there's something we don't understand - but we don't know what it is!

Probably not light - neutrinos have had their speed measured before with regard to a supernova observation and it was definately slower than the speed of light.

But neutrinos are tricky little beasts - we have only recently discovered that they have mass - it's just too small for us to measure

How do we know? - because they switch - there are three types electron, muon and tau neutrinos and they oscillate between them - a bit like Dr Jeckle, Mr Hyde and someone else - they can only do this if they have mass.

So what is it we don't understand? This is what has everybody scratching their heads - It would be nice if there was some fundamental physics this was uncovering, however it's likely to be something much more pedestrian like the way that neutinos interact with matter in the detector or some subtle thing to do with the way the clocks are synchronised

[naomi24]

//there's something we don't understand - but we don't know what it is! //

I think there's a helluva lot more we don't understand - but I'm no scientist.

[johnny37]

There are thing about the laws of physics we do not understand. In five billion years when the sun dies hopefully we wil have discovered how to get out here!

One of the things I do not understand is that neutrinos travel through solid rock.

[jake-the-peg]

There's a difference - for example

We don't understand how the physical constants have the values they do, we have very little idea about the underlying nature of time etc.

We have very little idea how to even go about investigating these questions.

However we have a very good model about how neutrinos should behave and that have been backed up by lots of experiments and observations - apart from this one!

That's the most exciting time - it means there's something we thought we understood but there's just something subtly wrong with it.

Like Newton's laws gave us the orbit's for all the planets - except Mercury - We needed General relativity to explain that.

Small oddities in spectra of light gave us quantum theory.

It's when you see small things that don't quite work that can cause the greatest upsets.

Thing is we don't quite know where to look - maybe it's to do with the way neutrinos interact - maybe it's something completely unexpected.

As for why they don't interact much with matter - that's no more surprising than why photons don't interact with glass

You're not surprised by that because you're used to seeing glass and light - you've not built up an inuition about neutrinos so seems strange.

Just imagine being a dark age peasant seeing glass in a cathedral in the first time - they must have been as amazed as you are about neutrinos

[Davethedog]

Einstein said we couldn't travel faster than light, however the theory of relativity is just that a theory. As such it has stood up for a long time but as our understanding grows its possible that some of his findings will be discounted. There were two instances of faster than light neutrinos, but as they cannot be explained nobody is rushing to publish.

Such is the way of science.

[d9f1c7]

The people running this experiment studied the outcome and repeated it for nearly 2 years before going public and even then they said we need help to determine our error, they did not declare FTL was possible, it was the media that did that. The problem is that if FTL is demonstrated to be possible then we have to tear up so many other theories and understandings so it becomes a more general question of understanding rather than just understanding light.

[naomi24]

The prospect of unknown potential! Exciting stuff!

[Old_Geezer]

I believe the equations show that nothing with mass can travel at the speed of light, but that there was no restriction to travelling faster than light. The trick being, is you have mass, to come into existence already travelling that speed. (Or I suppose find a way to jump from less than light speed to greater than light speed without travelling through light speed in the process.)

[d9f1c7]

Johnny they travel through solid rock because, like all matter they are 99.99999% empty space, there is nothing to hit. Neutrino detectors only work because occasionally one of them does pick out th 0.000001% and hits a nuclueus.

[jake-the-peg]

Ah there's a bit more to it than that!

For example glass is denser than paper but light goes through glass

You can't think about them as billiard balls "hitting each other".

Each force has an interaction constant - a "coupling constant" that charcterises how likely something is to interact with that force.

So for the electromagnetic force that constant "alpha" charcterises how likely an interaction is to happen - if you like what the probability is of a "hit" if two particles are within some range of each other for alpha this is about 1/137

Neutrinos are neutral and only interact with the weak force Alpha(weak) is about 1/1,000,000

That interaction is even weaker at high energies.

[Nebch]

Actually, the scientists conducting this experiment did discover where they made their error, thanks to the help of 'The Scientific Community'. What is ironic, is that the theory that would have been disproved (Einstein's) if the experiment was indeed correct, was the same theory which showed why the experiment came up with these results:

The theory states that time moves at different speeds based on how close to matter an object is: this is because matter affects "spacetime". This means that if time was being kept in two different places in the universe, it would effectively move at different speeds. This means that if light was being measured in one place, whilst neutrinos were being measured in another (which they were: a satellite, where the effects of the Earth's mass are less) then they would appear to show different results.
After the scientists at CERN rectified this mistake, neutrinos were indeed found to travel just under the speed of light, meaning that so far we do understand light :)

[rov1100]

Where's the link Nebch?

[scowie]

The neutrinos weren't measured at a satellite. They were measured at Gran Sasso lab in Italy. The synchronicity of the atomic clocks used would depend on satellites though, so time dilation effects may play a part there.

I believe it is still an open question as to whether these neutrinos actually travelled faster than light or not.

[flobadob]

Could the neutrinos have ridden the light waves like a surf board and been bunched up toward the front of the light beam so as to arrive before it, or where they both sent different ways?

[MarkRae]

Anything proven can be unproven in the light of progress. For 200 years we "knew" that Isaac Newton was right. Einstein "knew" that too for the early part of his life, right up to the moment when he could prove that Newton was wrong.

It would not surprise me in the slightest if Einstein's famous equation is shown eventually to be total hogwash...

[beso]

I expected better from you MarkRae.

Newton was not wrong. Man went to the Moon and back on Newton's equations. Einstein's equations reduce precisely to Newton's at non-Relativistic velocities.

If and when someone eventually advances beyond Einstein's work then the situation will be exactly the same. Einstein's equations will describe a special case of an unanticipated larger system.

Suggesting that Einstein's work could ever be considered "hogwash" shows profound scientific ignorance.

[MarkRae]

These days, General Relativity has essentially replaced pretty much all of Newton's work. Newton's laws came up with very close approximations, but failed to explain things like gravity's affect on time or gravitational lensing of light, both of which are tested predictions made by General Relativity. Relativity / Quantum Physics has certainly expanded the definition of physics and, in the broader sense, Newtonian principles don't always apply.

[beso]

Newton made no predictions about the effect of gravitation on light or Time. It was beyond the scope of his work and hence it remains incorrect to say that Newton was wrong.