The Webb Telescope Just Observed Faster Than Light Signals
The James Webb Space Telescope has seen signals that move faster than light. It’s true but it doesn’t mean that the speed of light limit was broken. Today I want to have a look at how apparent faster than light signals can be used in astrophysics to understand what happens in galaxies. But also at why some physicists, me included, think that faster than light signals might be real. This is what the James Webb Space Telescope has seen. It’s ripples around the supernova remnant Cassiopeia A that seem to race across space faster than light or “superluminal” as physicists say. And while these ripples really do move faster than light, it’s not in conflict with Einstein’s theories. It’s what’s called a “light echo”. To see how this works, let me draw you a simple example. We have a supernova going off and from the supernova there is a burst of light moving outward, in a sphere. Of course reality is a little more complicated, but this is basically the spherical cow of astrophysics. This sphere of light moves, would you know it, at the speed of light. Okay but now imagine that behind the supernova there is a cloud of dust and let’s assume it’s basically a flat plane. When the sphere of light hits the dust, that creates a reflection which we see.
We then have to ask what’s the speed of the ring at which the surface of the light sphere intersects the dust. And this speed turns out to depend on the angle at the intersection. In particular at first contact this angle is zero and the outward speed is actually infinite. So we see a ring racing outward at faster than the speed of light which then slows down.
This is why a light echo can be faster than light. It’s not that the dust moves faster than light and it’s not that the light moves faster than light. It’s that the intersection between light and the dust changes faster than light and this is what we see. The cool thing about this is that this apparent superluminal sweeps across the surface of the dust very quickly, so it’s a great way to create a tomographic map that tells you what the structures are.
And this hasn’t been the only recent superluminal observation in astrophysics. Near the centre of our galaxy, astronomers have tracked X-ray echoes from outbursts of the Milky Way’s central black hole. And in the galaxy Centaurus A, astronomers have seen a blob of matter emitted by a black hole jet that moves at two point seven times the speed of light.
Ok, but now for the question everyone is actually here for. Could faster than light ever be real in the sense of carrying information faster than light. The answer is that physics does have a few doors that are open mathematically. We label them “Do Not Enter”, then we peek. One intriguing example is the reason why quantum mechanics does not allow information to travel faster than light. It totally depends on the probabilistic interpretation of quantum physics. Indeed you can prove that if there is any tiny deviation from these probabilistic predictions, then you could use that to send information faster than light. Now, almost all physicists take this to mean that nature is fundamentally random in the quantum sense and that is what protects the speed of light limit. The only exception that I know of is Antony Valentini who thinks that the quantum randomness that we observe is a good approximation but not always correct. And this means that there are cases when information can travel faster than light. It’s a totally under explored argument I think. Faster than light motion also appears in many attempts to modify gravity, that includes approaches to describe dark matter. I have toyed with these theories myself and basically whatever you try, you always end up with some superluminal propagation. Now again, most physicists take this to mean that something is wrong with these theories. But I wonder. Maybe the mathematics is trying to tell us instead that we should seriously consider faster than light motion? And then there is Einstein’s theory of general relativity itself that allows certain types of travel faster than light. For one thing, it allows wormholes as shortcuts. You don’t actually travel faster than light through the wormhole. However, you will be faster than light that didn’t go through the wormhole. Warp metrics exploit another peculiar feature of general relativity, which is that while you can’t move in spacetime faster than light, spacetime itself can move faster than light. Physicists believe that this actually happened in the early universe, that space expanded faster than light. So mathematically, you can make warp drives work. For the time being though, we don’t know how to create and maintain either wormholes or warp metrics as these seem to require negative energy which, for the time being, is all being used up on Twitter.
