Stephen Hawking’s Grand Design started yesterday, so we thought we’d try and pretend that we were, maybe, half as smart are the eminent professor (maybe a quarter…or an eighth…) and try and put together some facts about the weird world of physics.
FACT 1: Black holes aren’t black. Like a very faint glow-worm in the vacuum of space they give off a tiny amount of light. This is called ‘Hawking radiation’, after Prof Hawking, who first proposed that it existed. As black holes emit this light they lose mass – so eventually, if they have no interstellar gas and light to feed them, they evaporate completely.
FACT 2: You can stop light (and, no, not by flicking the bedroom light-switch). Light is the fastest thing in the universe. However, its speed can be affected as it moves through other materials, such as glass or water. To stop light altogether, scientists cooled a gas of magnetically trapped sodium atoms to within a few millionths of a degree of absolute zero (-273 deg C). This would normally be opaque to light. But by illuminating it with a laser called a coupling beam, it becomes transparent, which allows another laser pulse to pass through it. And, incredibly, if the coupling laser is turned off while the probe pulse is inside the gas cloud, the probe pulse stops dead in its tracks. If the coupling beam is then turned back on, the probe pulse emerges intact, just as if it had been waiting to resume its journey.
FACT 3: A particle on one side of the universe can affect one on the other side of the universe. This is one from the weird world of quantum physics. It is called quantum entanglement. It’s possible to link together two quantum particles — photons of light or atoms, for example — in a special way that makes them effectively two parts of the same entity. You can then separate them as far as you like, and a change in one is instantly reflected in the other.
FACT 4: Following on from this, the US Department of Defence thought they could maybe utilise entanglement to send messages faster than light as the link between the photons is instantaneous. Sadly you can’t. For one you can’t predict what the photons are going to do, and if the message went faster than light it would arrive in the past before you sent the message, somewhat throwing cause and effect out the window.
There are lots of different types of quarks (and they’re different sizes). You’ve got top quarks, bottom quarks, charm quarks, strange quarks, up quarks and down quarks.
Particles are waves and vice versa.
FACT 7: Quantum physics is really all about probability. This is because before you start to measure what the quantum particle is doing, it can be doing an infinite number of things – so by ‘looking’ you determine what is happening.
FACT 8: Another way of putting this – because we struggled with this one – is that a quantum particle moving from point A to point B will take absolutely every possible path from A to B, at the same time. This includes paths that involve highly improbable events like electron-positron pairs appearing out of nowhere, and disappearing again. The full theory of quantum electro-dynamics (QED) involves contributions from every possible process, even the ridiculously unlikely ones.
FACT 9: Want to know the size of everything from a string, as in string theory, to the observable universe? We thought we’d leave this to clever bods than us – so go here, because it’s amazing!
FACT 10: Most of the universe is missing. There’s the stuff we can see, the stars and galaxies – probably 100 billion galaxies in the universe, each with between 10 million and a trillion stars in it – and all that only makes up a measly 2% of the mass of the universe. The rest is made up of dark matter and dark energy – though no one really knows what they are.
Watch the next episode of Stephen Hawking's Grand Design on Thursday 20th September at 9pm on Discovery.
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