Black Holes and Revelations – A review of February’s SciBar

Tony Padilla from the University of Nottingham is asking all of the big questions – “Why are we here?” Well Tony, it’s the VAT & Fiddle, it’s 7:30, it’s SciBar! Ah, he doesn’t mean that, he means, “Why do we exist? Why does the universe exist?”

The answer lies in black holes. There, the conditions are similar to the very start of the universe. There, we have a large amount of mass in a small amount of space.

But before we get to black holes, we have to look at speed. Usain Bolt is fast. But regardless of how many chicken nuggets he eats, he can never run at the speed of light.

The speed of light is always the same. If you have two cars, both travelling at 70mph away from each other then they are moving apart at 140mph. What happens if one of those cars is going at the speed of light? Does that mean that they are moving apart at the speed of light + 70mph? No, they are moving apart at the speed of light. This holds true even if both cars were travelling at the speed of light.

However, the theory of relativity does tell us that time slows down for a moving observer. So, when the stadium clock in Beijing timed Usain Bolt at 9:58 seconds, his own clock would have ticked slower by five millionths of a nanosecond. The really amazing thing is that this didn’t happen because he ran faster but because the track shrank!

To leave the planet earth, you need to travel at 25,000mph, this is the escape velocity. This speed is determined by the size and mass of the planet. If the Earth was smaller then the speed would go up. If the Earth was the same mass but the size of a 5p piece then you would need to go faster than the speed of light in order to escape.

So what’s a black hole? When a star runs out of fuel¬† it starts to collapse under its own weight. The neutrinos in the star don’t want to be too close together which stops the collapse and causes a supernova. After that we are left with a neutron star that pulls in nearby matter. When this collapses under its own weight, we get a black hole. It is so dense that not even light can escape. The star continues to collapse to a single point, called a singularity.

While nothing can escape a black hole, Oscar winner Eddie Redmayne could tell us that on a quantum level they give off Hawking Radiation. This means that it’s possible for black holes to decay, although this happens incredibly slowly.

Now, physicists don’t like the singularity at the heart of the black hole because the theory of relativity tells us that the gravitational forces would be infinite and they don’t like infinity. Hence they needed to come up with a quantum theory of gravity.

One of these theories is “String Theory” – this replaces particles with vibrating strings. These have finite length but are no longer points. One of the big things that string theory predicts is that we live in 10 dimensions (9 of space and 1 of time) Physicists like string theory because you can get Newtonian gravity from it while this isn’t true of some other theories.

But where are these extra dimensions? They could be wrapped up in a way that means we can’t experience them or there could be parallel worlds! Imagine being an ant living on one wall in a room. As far as you know the world is 2 dimensional, you know nothing about the opposite wall. So, while we can experience our 4 dimensional existence, we don’t know what else is out there.

But how do you prove string theory? That’s where our old friend the LHC comes into play. If two particles collide and some of the energy disappears, could it have vanished into an extra dimension? Other physicists are also looking for disappearing energy to try and find dark matter but this would give off a different energy signature.

So, a great talk and I thought that I just about understood it. Then the Q and A session started and that was when a lot of things started going over my head. I just about understood why you can’t go faster than the speed of light – as you get closer to that speed your mass increases towards infinity and so you need infinite energy. The reason that photons can travel at the speed of light is because they have no mass.

After that, the physicists in the audience started asking more technical questions. Tony dealt with them all very well. Although at one point he started talking about throwing Gary Neville into a black hole (turns out that Tony is a bitter Liverpool fan)

So, all in all, another great evening. SciBar is back on its usual day in March and returns to the VAT & Fiddle on the 25th of March with a talk entitled, “Ebola – were we ready?”