There has been a lot of talk this year about that physicist guy Albert Einstein, the fellow with the wild hair. Why are people talking about him?
It is because 2015 marks a century since the publication of Einstein’s most important work, his General Theory of Relativity. It was published on November 25th, 1915, 100 years ago yesterday.
What is that?
It is a set of 10 mathematical equations that revolutionised our scientific understanding about how gravity works.
We know how gravity works; didn’t Isaac Newton tell us all that centuries ago?
Newton told us a lot about gravitational attraction but he couldn’t explain all the strange things astronomers can see in space. Einstein’s General Relativity made sense of this and much more, mainly about how massive objects are able to have an effect on space and time, the “space-time continuum”.
That sounds like something from Star Trek
Maybe so but Einstein’s equations were able to explain the universe and gravity and the gravitational pull of massive objects better than anyone who had come before. And his theories about gravity and space-time have been proven to be correct over and over again in astronomical experiments.
This is all stuff for physicists and scientists. What difference does any of this make to me?
For one thing, the GPS you use on your smartphone depends on being able to make small time corrections, and these are explained by Einstein’s relativity. It predicts that time is not universally fixed and can seem to run slower for a clock moving at high speed in orbit compared with a clock sitting on Earth.
But the accuracy of GPS is dependent on clocks on Earth and in orbit matching up, so small adjustments for this are built in to the GPS system.
Maybe, but I still don’t get why Einstein is so famous
Look at it another way. Newton is famous for, among other things, explaining the gravitational pull between Earth and sun, and Earth and moon and any large bodies. We are told he decided to study this when a falling apple hit him while he was sitting under an apple tree, and his discoveries made him famous.
Einstein made similarly ground- breaking discoveries.
Like what? And leave space-time out of it
In 1905 he worked as a clerk in a patent office. He was a genius at maths but was not connected to any university or research centre. This didn't stop him from completing and publishing four important papers during that year in the Annalen der Physik scientific journal.
They were so important and groundbreaking that 1905 was later referred to as his Annus mirabilis – or extraordinary year – and this when he was just 26. The first of his papers won him a Nobel Prize 16 years later, in 1921. This was for research into the "photoelectric effect".
At that time there was a big dispute over whether light was made of waves or particles. People set up experiments and showed it was a wave.
Einstein helped to settle the dispute, by proving light could also definitely be a particle he called an “energy quanta” (today we call it a photon). This made people accept that light acted like a wave in some contexts and a particle in others.
By the way, the ideas he developed explain how night-vision goggles work, so that is something practical that came from it.
Okay, he proved light photons exist, but is that all?
He published a paper in July 1905 on “Brownian motion”, in the process providing proof that atoms really exist. Everyone knows today that atoms exist but that wasn’t the case in 1905. Not everyone accepted the simple explanation that they were like tiny billiard balls.
Brownian Motion is a phenomenon first described in 1827 by botanist Robert Brown. He noticed microscopic particles being pushed about on an apparently stationary liquid, but no one could come up with an explanation for what force was driving this motion.
Einstein used his mathematics to describe how the particles were being knocked about by water molecules, effectively proving the existence of atoms and molecules.
This was another example of how Einstein’s work was able to make major contributions to our understanding of the physical world.
All right, I see that. What else is in those 1905 papers?
He discovered “mass-energy equivalence”, which he wrote about in another paper, published in November of that year. This is the relationship between mass and energy that says mass is concentrated energy. The mass of something is a measure of the energy it contains.
This led to his famous formula E = mc2: the amount of energy released by mass is equivalent to that mass times the speed of light squared. This is a lot of energy, and it explains the energy produced by nuclear reactors or nuclear weapons. That is probably the best-known formula in the world, but not everyone knows where it came from or what it means.
Then there was his special theory of relativity, which begins his work on the relationship between space and time, work that reached its culmination in general relativity.
In this he proved that light always moves at a constant speed, no matter what. So if you are in an aircraft moving at 500mph and you switch on a light, an observer on the ground does not see the light moving at light speed plus 500mph.
Special relativity also says that the laws of physics don’t vary for any observer as long as they are not accelerating.
I suppose this brings us back to general relativity?
Yes. It might be difficult to understand but it has been proven to be correct time after time. For example, Einstein predicted that light, which normally travels in a straight line, would bend slightly if it passed close to a massive object, and that was shown to be true.
He described the universe as having not three but four dimensions: the three we know plus time – the space-time continuum – and that time could change and space could be distorted by massive objects such as stars and planets.
His work adds up to one thing: that he is the greatest scientist yet known, surpassing even the great Isaac Newton.
