# Science Questions

## If neutrinos move faster than light, is time travel possible?

Sun, 20th Nov 2011

### Question

Hi Chris,

The question I'd really like to ask is... Following the reconfirmed results that a neutrino can travel faster than light, why is it then assumed that travelling through time is possible?

A neutrino  coming from the sun would still take several minutes to reach Earth, say, even if it does get here faster then a ray of light that left at the same time. In the media I haven't found the answer to this question, I just come across the assumption!

Cheers,

Shane Record

Dave - Essentially, if you take all of Einstein’s equations – the first thing it says is that to go at the speed of light, you need an infinite amount of energy which kind of means if you go any faster than the speed of light, if you get out of the speed of light, you need, in fact, energy and all the equations explode, and everything breaks.

But if you put the numbers where you're going faster than the speed of light in there, you sort of get some results which seem a bit more meaningful.  It gives the appearance that light – that time appears to be going backwards for you if you are travelling faster than light.

And it essentially makes the direction which you're travelling in seem to look a bit – mathematically - it look more like a time axis and certain time look more like a normal axis.

So, it’s possible that space and time gets really confused for you if you're going faster than the speed of light.  But fundamentally, what I've said at the beginning was that all of our maths, our physics, breaks if you can go faster than the speed of light which means we don't really know until we can actually test it, and we get a better theory.

#### Make a comment

If there is a speed faster than light, then there can only be one preferred reference frame in which that speed is the same in all directions. In a reference frame moving relative to the preferred reference frame, the thing which is faster than light may arrive before it left when moving in one direction, but it will be delayed by the same amount when moving in the opposite direction. Therefore, there is no violation of causality.

Even if you could send a message instantaneously in the preferred reference frame, you could not send the message to your own future. A 2-way communication, which is instantaneous in the preferred reference frame, could arrive before it is sent, but the reply could not be received before the original message was sent.

That is true because, in special relativity, with motion in the x direction, time depends on the x coordinate. Clocks farther ahead in location show later times.

Time travel is not possible. Phractality, Mon, 21st Nov 2011

Almost certainly not.  causality may change a bit at tiny scales but not at ours. Soul Surfer, Mon, 21st Nov 2011

IF a neutrino travels faster than C & time reverses, this would provide explanation of how the universe recycles? As is, universe is expanding & accelerating? CZARCAR, Mon, 21st Nov 2011

Neutrinos travelling through space are slower than c (supernova 1987A) so maybe it is only when they travel through matter they cam be faster? It has been suggested that they take a short cut of some kind.

Time travel is impossible for so many reasons.... Silver, Tue, 22nd Nov 2011

"the reconfirmed results that a neutrino can travel faster than light?"

Now, whenever did that happen?
Maybe you mean this?

"The new version of the Opera experiment changes the time structure of the particle beam that travels between Cern and Italy’s Gran Sasso laboratory. Instead of 10-microsecond pulses, the beam will now send much shorter 1-2 nanosecond pulses, with a 500-nanosecond gap in between.

This should allow the researchers to correlate the deparature and arrival times of every batch of neutrinos.

“For every neutrino event at Gran Sasso, you can connect it unambiguously with the batch of protons at Cern,” said Cern research director Dr. Sergio Bertolucci.

The new experiment will run until November, when Cern will stop accelerating protons and start accelerating lead ions. Researchers hope the results will shore up their yet-to-be-published paper about the faster-than-light phenomenon.

Two other teams currently working on experiments at Gran Sasso are scheduled to cross-check Opera’s data next year."

It's the first of December as I write this. yor_on, Thu, 1st Dec 2011