Fact Impact: Relativity

25 January 2011

Interview with

Andrew Pontzen

  • Relativity was born in 1905 when Albert Einstein published a seminal work titled "on the electrodynamics of moving bodies".
  • Albert Einstein during a lecture in Vienna in 1921 (age 42).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...
  • Hermann Minkowski...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...
  • Albert Einstein... 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.

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