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More on the faster-than-light neutrinos

I had previously mentioned the news that an experiment in CERN has suggested that some neutrinos are travelling faster than light. If you want some perspective on it, you can refer to two articles, one by Victor Stenger and another by Sean Carroll, both physicists and popular writers.

The beauty of the whole thing is that the experimenters themselves admit that they could be wrong. That is one of the strengths of science. The process involves looking at all results skeptically, and look for evidence. Ask for confirmation and re-check. Science actively works at proving others wrong and thus, what we end up with is only those ideas that have withstood numerous attempts at falsification. That is what makes it such a good method of acquiring knowledge.

Back to the topic, both the authors are saying that the result is probably the result of a systematic error, but also add that even if such a violation was confirmed to be true, it will not disprove Einstein much.  I learnt something there that I didnt know before. It seems, Einstein only says that you cannot make a particle travel at the speed of light, but if some particle is already travelling at the speed of light or more from the beginning(?), that does not violate Einstein’s equations.

Einstein’s equations fully allow for particles to travel faster than light — provided they never travel slower. Physicists have speculated about such objects for years. They are called tachyons. Many searches have been conducted, with no significant signals until now.

Einstein showed that it was impossible to accelerate a particle moving less than the speed of light (in a vacuum) to the speed of light or higher. Similarly, a tachyon cannot be decelerated to or below the speed of light. Only massless particles, such as photons, travel at exactly the speed of light.

Says Victor Stenger and continues:

So, if confirmed, the reported result from CERN or any future observation of superluminal motion will not lead to the overthrow of Einstein’s theory of relativity. Its significance will be to overthrow the distinction between cause and effect. At the worst, Einstein might be faulted for taking causality a little too seriously.

How does this happen? Let us try this simple thought experiment. Imagine that a ball could be thrown at a speed faster than the speed of light. Imagine a scenario similar to something as seen below. A is throwing a ball at B and the whole process is observed by E.

Can effects precede causes?

Let red line be the path of the ball from A to B. Since as per our assumption, the ball travels faster than the speed of light. Let us assume that this motion from A to B takes 9 seconds (note that B is very close to E).

Let the green line be the line of vision of E looking at A throwing the ball. This information needs to reach E for him to know that A has thrown the ball. Let us assume this takes 10 seconds (less than the nine seconds of the ball since the ball is travelling faster than the speed of light).

Let the purple line be the line of vision of E looking at B receiving the ball. Since B is very close to E, this information reaches E in just half a second.

Now you can see what happens. Once the ball leaves A’s hands, it reaches B in 9 seconds. The information that B has caught the ball reaches E in half a second. That is, E sees B receiving the ball in 9.5 seconds. But the information of A having thrown the ball, reaches E only at 10 seconds. So, to E, it appears that the cause, A throwing the ball, appears after the effect, B catching the ball. This is the problem with superluminal objects.

But then again, Sean Carroll, in another post, argues that even faster than light particles will not violate cause and effect relationship. Frankly, it is all over my head. But there is one thing that I firmly understand.

The universe is positively weird.

Note: For more details on the experiment, you can also look at this webcast from CERN where the scientists have presented their findings. I am yet to watch it, it is almost 2 hours long.

  1. R
    October 10, 2011 at 22:18

    Just imagining how the scenario would be like if E thinks that B is going to throw the ball 🙂

    • October 13, 2011 at 15:05

      If the movement of the hand throwing a ball is exactly the reverse of catching one, then E could think that B threw the balll first. But since the movements are different, he might only end up confused. 🙂

  1. November 20, 2011 at 19:23

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