Black holes, big bangs: 100 years of relativity

Genius: Einstein said that “the true sign of intelligence is not knowledge but imagination”.

Exactly 100 years ago, Albert Einstein gave a lecture which changed how we think about the universe forever. It was an extraordinary moment. What did he say? And why does it still matter?

In 1905, Albert Einstein wrote a series of papers that changed the world of physics three times.

First, he proved that everything is made from atoms, and then that light is made from particles.

In his third paper, he proved that light travels at the same speed for everyone — no matter where you are. A person standing on the equator is either moving at 0 mph or 1,040 mph depending on your perspective — but light always travels at the same speed. Yet speed equals distance divided by time. So for light to remain constant, space and time must change to accommodate it. This third discovery is known as the special theory of relativity.

Ten years later, on November 25th 1915, Einstein presented his general theory of relativity to the Prussian Academy of Sciences. Our understanding of the world changed again.

When Isaac Newton explained the force of gravity, he conceived of the universe as a box: all objects, including earth, were moving in a still, empty space. But how can gravity work if nothing connects these objects? Einstein’s theory sees the universe differently: it is more like a jellyfish which can expand and contract, moving and twisting within. Objects are not suspended in empty space: gravity is that space, and it keeps everything in motion.

Large objects — like the sun and the earth — use gravity to keep things in orbit, because Einstein’s theory supposes that space and time curve around them. Like marbles rolling around a funnel, satellites circle stars and planets. And time measured in Earth’s orbit moves faster than time on the ground.

From here, scientists have predicted some amazing conclusions: Einstein’s equations imply that the universe is expanding, and if that is true, it must have begun with a very small space — this is now known as the Big Bang. It also implies the existence of black holes, which Einstein said would be “a true disaster”. They turned out to be real. Time and again, this unlikely century-old theory proves itself correct.

It’s all relative

Einstein was undeniably a genius, say some, but his theories are too difficult for many people to grasp. It is simple ideas which truly make a difference — ideas like democracy which promotes political equality, or vaccinations which prevent disease. Einstein’s theory is grand, but it did not change our daily lives.

But relativity has made a difference, others argue, just in less obvious ways — even GPS could not work without it. Besides, with some dedicated thinking, Einstein’s theory can suddenly “lift the veil” on the universe with breathtaking simplicity, and this understanding is worthwhile in itself. “The reward is sheer beauty,” says the physicist Carlo Rovelli.

You Decide

  1. Did this story change how you see the world?
  2. “Most people say that it is the intellect which makes a great scientist. They are wrong: it is character.” — Einstein. Do you agree?


  1. List five other ideas which changed the world.
  2. Draw a diagram showing how the Earth orbits the sun.

Some People Say...

“Only two things are infinite, the universe and human stupidity.”

Albert Einstein

What do you think?

Q & A

I don’t understand.
That’s perfectly normal — Einstein was the greatest scientist of the twentieth century, and it took him years to understand his own theories; he even changed his mind about certain elements several times after he published them. Scientists also spend decades thinking about these things — so don’t worry if you don’t grasp them all in one go.
Is there another Einstein out there?
Einstein’s theory attempted to explain the universe, and 100 years later leading physicists are still discovering new information. There is much they do not know — about black holes, particles, ‘dark matter’ and parallel universes, to name a few topics. But their knowledge is expanding all the time — soon ‘another’ Einstein may well explain the world in a way that we have never thought of before.

Word Watch

In our daily lives, light is a simple concept to understand. But in physics, it is complex and mysterious, behaving as both a particle — known as a photon — and an electromagnetic wave. Scientists continue to debate how this can be possible.
1,040 mph
As the earth spins, an object on the equator travels around 24,901 miles per day. This distance divided by 23 hours, 56 minutes and four seconds indicates a speed of 1,040 mph. Calculations by the data scientist Seth Kadish.
Big Bang
This is the idea that everything in the universe began in a very small, very dense point. With a huge amount of energy, all of this matter suddenly exploded outwards, forming the universe.
Black holes
These ‘holes’ appear in space when an dense object with a huge amount of mass — such as a collapsed star — has such a high gravitational pull that even light cannot escape it.
Global Positioning Systems use clocks which are accurate to a few billionths of a second. Because the clocks in space move faster than those on the ground, Einstein’s equations are used to account for the difference.


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