If we can find a nice, coherent beam of light in space (in other words, a natural space laser), and that beam of light travels over billions of years to our telescopes, we can measure the spread in energy and use that to measure the frothiness of space-time. But thankfully, nature can provide a laboratory for us. This effect is incredibly, incredibly minute, so tiny we couldn't possibly hope to measure it in a laboratory. The net effect is that light traveling through a frothy space-time will slowly spread out in energy. Sometimes those little jostles will give the light a boost, nudging up its energy level, and sometimes the light will encounter a little speed bump, slowing it down. For example, a beam of light going along its merry way will encounter all sorts of microscopic bumps and jostles - a Planckian gravel path rather than a smooth highway. If space-time really is frothy and bubbling, then this should affect anything passing through space-time. So if we could crack open space-time and have a look at the tiniest of scales, maybe we could get some clue as to what's really going on. ![]() And no, we do not currently know what that ultimate answer looks like. Physicists think that the ultimate answer lies in a combination of the two views, something called quantum gravity. Either general relativity is correct and space-time is smooth, or quantum mechanics is correct and space-time is chunky. Related: The universe: Big Bang to now in 10 easy stepsīut both of these views of space-time can be correct at the same time. Instead, it should be a roiling, boiling mess - an angry frothing soup of particles, constantly tearing holes in space-time and patching them up again before anyone in the macroscopic world notices. And nothing can ever be known for certain.Īnd so, as the physicist John Wheeler pointed out in 1960, if we were to zoom down to the tiniest possible scale (something called the Planck scale, which is about a billionth of a billionth of a billionth of a billionth of a meter), space-time shouldn't appear smooth at all. Fields can wiggle and vibrate with a will all their own. Particles can appear and disappear at a moment's notice (and usually even less time than that). In the quantum world, everything microscopic is ruled by random chance and probabilities. We also have quantum mechanics (and its successor, quantum field theory). Without this smoothness, the mathematics of gravity simply break down.īut general relativity isn't the only thing telling us about space-time. No matter how far you zoom in, space-time will always be as wrinkle-free as a recently ironed shirt. In order for the math of general relativity to work, this fabric of space-time has to be absolutely smooth at the tiniest of scales. In the language of relativity, matter and energy bend and warp the fabric of space-time, and in response the bending and warping of space-time tells matter and energy how to move, something we collectively experience as " gravity."
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