Astronomers hope to compare such models with images of the black hole made with the Event Horizon Telescope, to look for any deviations from general relativity. A weighty particle Gravitational waves also may reveal physics beyond relativity in other ways, notes Kent Yagi, a theoretical astrophysicist at the University of Virginia. One way is simply by constraining parameters like the mass of the graviton. If this particle has no mass, then gravitational waves should move at the speed of light, he says.
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Albert Einstein's work is often used as a waypoint from which other science begins or extends. I t is the biggest of problems, it is the smallest of problems. At present physicists have two separate rulebooks explaining how nature works. There is general relativity , which beautifully accounts for gravity and all of the things it dominates: orbiting planets, colliding galaxies, the dynamics of the expanding universe as a whole.
Then there is quantum mechanics , which handles the other three forces — electromagnetism and the two nuclear forces. Quantum theory is extremely adept at describing what happens when a uranium atom decays, or when individual particles of light hit a solar cell.
Now for the problem: relativity and quantum mechanics are fundamentally different theories that have different formulations. It is not just a matter of scientific terminology; it is a clash of genuinely incompatible descriptions of reality. The conflict between the two halves of physics has been brewing for more than a century — sparked by a pair of papers by Einstein , one outlining relativity and the other introducing the quantum — but recently it has entered an intriguing, unpredictable new phase.
Two notable physicists have staked out extreme positions in their camps, conducting experiments that could finally settle which approach is paramount. In general relativity, events are continuous and deterministic, meaning that every cause matches up to a specific, local effect.
In quantum mechanics, events produced by the interaction of subatomic particles happen in jumps yes, quantum leaps , with probabilistic rather than definite outcomes. Quantum rules allow connections forbidden by classical physics. This was demonstrated in a much-discussed recent experiment in which Dutch researchers defied the local effect. They showed that two particles — in this case, electrons — could influence each other instantly, even though they were a mile apart.
When you try to interpret smooth relativistic laws in a chunky quantum style, or vice versa, things go dreadfully wrong. Relativity gives nonsensical answers when you try to scale it down to quantum size, eventually descending to infinite values in its description of gravity. Likewise, quantum mechanics runs into serious trouble when you blow it up to cosmic dimensions.
Quantum fields carry a certain amount of energy, even in seemingly empty space, and the amount of energy gets bigger as the fields get bigger. Go big enough, and the amount of energy in the quantum fields becomes so great that it creates a black hole that causes the universe to fold in on itself. Craig Hogan, a theoretical astrophysicist at the University of Chicago and the director of the Center for Particle Astrophysics at Fermilab, is reinterpreting the quantum side with a novel theory in which the quantum units of space itself might be large enough to be studied directly.
To understand what is at stake, look back at the precedents. It provided the conceptual tools for the Large Hadron Collider , solar cells, all of modern microelectronics.
What emerges from the dust-up could be nothing less than a third revolution in modern physics, with staggering implications. It could tell us where the laws of nature came from, and whether the cosmos is built on uncertainty or whether it is fundamentally deterministic, with every event linked definitively to a cause.
The clash between relativity and quantum mechanics happens when you try to analyse what gravity is doing over extremely short distances, he notes, so he has decided to get a really good look at what is happening right there.
But Hogan questions whether that is really true. Just as a pixel is the smallest unit of an image on your screen and a photon is the smallest unit of light, he argues, so there might be an unbreakable smallest unit of distance: a quantum of space.
There would be no way for gravity to function at the smallest scales because no such scale would exist. Or put another way, general relativity would be forced to make peace with quantum physics, because the space in which physicists measure the effects of relativity would itself be divided into unbreakable quantum units. The theatre of reality in which gravity acts would take place on a quantum stage. Hogan acknowledges that his concept sounds a bit odd, even to a lot of his colleagues on the quantum side of things.
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