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from the show Antimatter Storms and the Universe's Dark Ages
- Relativity was born in 1905 when Albert Einstein published a seminal work titled "on the electrodynamics of moving bodies".
- As that name suggests, Einstein analysed the electronic behaviour of particles moving at high speed...
- ...but he realised that the implications of his theory extended way beyond that original motivation.
- In the same year that Einstein laid this ground-work for relativity...
- ...he also discovered a crucial foundation of quantum theory...
- ...explained how a bit of dust moves around in the air, by constant bombardment from microscopic air molecules
- ...and used his new "relativity" theory to show that E = mc2.
- It was the lesser-known Hermann Minkowski who later showed that Einstein’s ideas could be expressed in the beautiful mathematical language of spacetime
- Einstein went on to spend eight years worrying that Newton's laws of gravity were not compatible with Minkowski's spacetime...
- ... ultimately leading to Einstein's 1915 paper which introduced "general" relativity, a new version of gravity...
- ...that was not only compatible with, but actually founded on, Minkowski's idea of spacetime.
- Einstein predicted a whole slew of counterintuitive effects from his relativity theories...
- ...if you travel at 100 miles per hour for 100 years, your watch will lose 35 microseconds compared to an identical watch left stationary
- ...but if you sit still for 100 years on a stepladder 100 metres tall, the tiny difference in gravity means your watch will gain 35 microseconds compared to an identical watch on the ground
- ...So, clocks on high-altitude orbiting satellites should lose 7 microseconds per day because they're orbiting so fast
- ...but should gain 45 microseconds per day because they're so high up, so an overall gain of 38 microseconds per day
- ... a prediction that's been verified again and again in experiments, and is actually used every time a satellite navigation system calculates its location.
- General relativity is the key building-block in our modern understanding of space and the universe
- ... it explains why mercury's orbit does not quite agree with the prediction from Newton's gravity...
- ... it correctly describes how the path of light is bent when it passes near massive objects – everything from stars to galaxy clusters
- ... it predicts gravitational waves, the existence of which have been indirectly confirmed by watching how the rate of a pulsar changes over time...
- ... it gives us a framework to describe the universe from a tiny fraction of a second through to today, 13.6 billion years...
- ... for instance describing precisely how the overall expansion of the universe is affected by the gravitational pull of matter within the universe...
- ... leading to exact predictions which match the real universe in exquisite detail.
- But relativity cannot be a complete theory of spacetime and gravity...
- ...the combination of Einstein's original relativity theory with quantum mechanics gives quantum field theory, the incredibly successful theory of fundamental particles
- ...but the combination of general relativity with quantum mechanics leads to mathematical nonsense
- ...meaning that gravity cannot be accommodated within quantum mechanics
- ...which troubled Einstein for the rest of his life
- ...and has led to a myriad of speculative mathematical ideas like string theory and loop quantum gravity
- ...none of which have yet been experimentally confirmed or rejected by cosmologists or physicists.