Although the guts of General Relativity are mathematical, and for decades relegated to math departments rather than proper physics, you will experience the technological gift of relativity every time you navigate your way to your favorite restaurant. GPS, the global positioning system, consists of a network of orbiting satellites that constantly transmit accurate timing data. Your phone compares signals to determine where you are on Earth. But there is a difference in spacetime between the surface of the Earth and the orbit of the satellites. Without paying attention to general relativity, your navigation will be wrong, and you will be late for dinner.
As revolutions go, general relativity is a big one. And as unity goes, this is a warning. For this unification to happen, Einstein had to radically, permanently change not only our concepts of gravity as a force that moves through space and time, but our concepts of space and time itself. It will require nothing less than a complete overhaul of our entire philosophical understanding of the relationship between space and time to bridge the gap.
And as Einstein would find in the following decades, up to the time of his death, that bringing other forces such as electromagnetism into the same unified field was impossible. Electromagnetism, and other forces, cannot be accounted for in the same way. Instead we have to use quantum probabilities to make predictions, and if we use the same technique for gravity we only get infinities.
This is Einsteins waking dream. This is the demon that haunts the equations. It is the wedge driven between the force of gravity and electromagnetism. It is the intractable thorn that prevents us from achieving the nirvana of unity. And like the unifications of the past, from Newton and Maxwell and Einstein, to solve this, to crack this infernal puzzle, moving around or passing through or between the infinities, will require a complete revolution in our understanding of the very fabric of truth.
Fortunately, we are not alone in our quest. The dream of unifying the great powers of quantum and gravitational physics did not end with Einstein’s death, and since his passing hundreds of physicists have taken up the mantle, contributed to the cause in some small or significant way, and passed on their learning. to the next generation.
That long-cherished quest is far from over, but in the past nearly century a contender has risen to the top, a collection of unique ideas that one day hopes to solidify into a proven an, complete theory of the physical universe: string theory. And string theory has come up with a strange idea: that our universe is not what it seems. It is called the holographic principle, it says that our universe is not the familiar three dimensions of our existence, but only an impossibly thin two-dimensional membrane. In this framework, all the information within the universe can be dropped onto it, without losing even a bit, and once gravity itself disappears, replaced by more familiar quantum forces.
This is holography in action. Mapping from the universe to its boundary preserves all the necessary information. The main goal of holography has been achieved. That in itself is a strange and unexpected joy, that nature should allow such mapping to happen in the first place. But then it goes a step further. The best way to solve quantum gravity, it seems, is to use holography to make gravity itself disappear. No more messy math messes, no more stacks of infinities, no more convulsions in spacetime. It’s just a normal quantum theory that we’ve become adept at solving with normal quantum tools.
So far this holographic idea has only been speculation. But it has a huge amount of promise.
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