Imagine a water world where intelligent life evolved not knowing about anything other than water. They probably wouldn't notice all the water. Over time a Galileo fish might discover it can learn about physics if it treat this medium they're embedded in as a separate material so they can work out a simple set of rules. Eventually discoverers might make it to the surface and begin to study the universe outside paving the way for a Newton and beyond. It's a fantasy we like to think about - the ice locked warm oceans of Europa come to mind. But it turns out we have some fish perception issues too.
Galileo learned you can simplify science by stripping it down to the basics. Drop a ball and a feather? Sure - remove the influence of air and they fall at the same rate. You can later add the influence of the air and understand the motion you see. Newton took this simplification of physics and ran with it . He found an simple way to account for gravity by sweeping the heavens clean. The planets traveled through space and space was a void. There were some serious problems with the theory, but it was fantastically successful and science shoved a few glaring flaws under the rug. Until James Clerk Maxwell came along.
Maxwell (I count three really important physicists - he's one of them) was hot on the trail of understanding electricity and magnetism. Telegraphy had become important and people were beginning to develop motors and lights. A theory of how these two forces worked was needed. Experiments suggested they were intimately related. Around the time of the American Civil War Maxwell decided to approach the problem with a mechanical model hoping to create an analogy to electricity and magnetism The model was almost ridiculously complicated. Magnetism took the form of vortices and the electric fields were greased balls that circulated around the vortices. But it worked. From it he got a consistent set of equations we call Maxwell's Equations. He threw away the model, but kept one part - there was a material substance he called the luminiferous ether.
Maxwell loved the idea of the ether. A devout Christian, he wrote:
The vast interplanetary and interstellar regions will no longer be regarded as waste places in the universe, which the Creator has not seen fit to fill with the symbols of the manifold order of His kingdom. We shall find them to be already full of this wonderful medium; so full, that no human power can remove it from the smallest portion of space, or produce the slightest flaw in its infinite continuity.
If you've had a year of college physics you're smiling and thinking "ah, but Einstein proved him wrong".. In 1905 Einstein showed light could be thought of as a packet of energy - a particle called the photon. He regarded the ether as problematic and noted his photons would easily travel through the void of empty space. Newton would have given Einstein a high five.
About fifteen years later Einstein changed his mind. While he still believed in the void of empty space, he wrote that ether would be okay if it obeyed special relativity. More interesting was his general theory of relativity made space-time a dynamic material. In it gravity is not a force but rather the bending of space-time caused by the presence of a mass. It turns out space can weigh, it can warp, bend and conduct waves.1 A material - an ether of sorts.
Now for the big jump. Empty space isn't empty. There are fields that permeate space.. You've probably heard about the electromagnetic field and the gravitational field. There are a couple of others - the Higgs field and there's another for quarks and gluons. The last one is worth talking about. What we call particles are wonderfully described as excitations in their fields.
Peering through an impossibly good microscope with an impossibly good eye you would see there is something everywhere in space. This little video is a simulation of the gluon field density of empty space Gluons bind quarks together to form the protons an neutrons that we're made of. Some excited regions areas have higher densities . These excitations are spots that, zooming out, we would define as something like a quark, electron or something else depending on the field
This two second simulation represents a small space about a millionth of a billionth of a meter on a side and it's slowed by by a million-billion-billion times.2 This is what all of "empty" space looks like - what is called the vacuum.
Think of the universe as an enormous lava lamp.
The absence of excitations we call matter is not an absence of structure. The vacuum is very much a material with properties you can measure .. Now for a bit of fun. Since we're much larger than these tiny regions we can measure bulk properties. For example in a fluid viscosity - the resistance to deformation - results from some complex quantum mechanical behavior, but we can easily measure the bulk property of a a liter of the fluid and get the same result an impossibly complex calculation would give,. You can measure the viscosity of the vacuum - it's been done and the result is about twenty pascal-seconds. Those of you who are mechanical engineers might be sitting up now. That's a figure in the range of fluids we're familiar with. In fact it's almost exactly the same as the viscosity of Hersey's chocolate syrup at room temperature. (somehow it made me very happy to realize that)
There are some important take-aways here. First is there is an ether of sorts - the vacuum is in every sense a material and not a void.. At the same time for worrying about how things happen on Earth at our scale Newtonian physics is a dandy approximation and you think in terms of it when using it. It breaks down when things are small or moving very fast, but that's where relativity and quantum mechanics are useful. And if you wonder about questions like "where does mass come from" and other deep questions at the frontier, you have to think about what the vacuum is.
__________
1 The "weight"is the so-called cosmological term that Einstein threw out because he didn't know about the expansion of the universe. The density of space-time has been measured to be about 6 * 10-29 g/cm3. The warping (orbit happen here) and bending are part of how gravity works and conducting waves are the recently confirmed gravity waves.
2 The cube is really completely full.. here red represents higher densities and the lowest densities are set to clear to allow you to see the action inside.
I love this one! Your best post. I have questions for you.
Posted by: Jheri | 04/19/2018 at 12:26 PM