Far out cosmology: space is not a medium (Introduction)

by David Turell , Saturday, December 07, 2024, 18:26 (15 days ago) @ David Turell

like a Cheshire cat:

https://bigthink.com/starts-with-a-bang/fabric-space-cheshire-cat/?utm_source=rejoiner&...

"As absurd as it may seem, what we think of as “empty space” doesn’t have the properties fundamental to all media that waves travel through, making the fabric of space the Cheshire Cat of the very Universe itself.

***

"When it comes to how waves work, one of the simplest examples you can experiment with for yourself is to simply drop a stone into an otherwise still body of water, such as a pond or a puddle. As the stone strikes the water, it pushes the water down and out-of-the-way. This leads to a crest (or high point) forming in a circular pattern around where the stone struck the water, followed by a trough (or low point) behind it. Most often, a series of crests-and-troughs are produced: what physicists understand as a wave or a wave pattern. These waves are disturbances in the water itself: the water serves as a medium for this wave to travel through, and the wave propagates at a particular speed dependent on the properties of the water itself.

***

"Although there are many types of waves we encounter in our daily lives — sound waves, water waves, seismic waves, etc. — these are all examples of the same class of wave: traveling waves, which propagate across or through a medium, as opposed to standing waves. Water waves travel through the body of water itself; seismic waves on our planet travel through the Earth; sound waves typically travel through the air. The sensation of hearing arises when that air, full of compressions (peaks) and rarefactions (troughs) in density, then pushes against our eardrums, causing the hairs within our cochlea to vibrate, stimulating the nerves that detect sound.

***

"If light travels through a medium, and Earth is in motion, then we should be able to detect that motion with a sensitive enough experiment. That’s precisely what the Michelson-Morely experiments did in the 1880s: the same experiment we thought about with water ripples created in a river, but with light and the moving Earth rather than with water and a flowing river.

"Remarkably, the experiments found no evidence for this medium — or any medium — at all. Light traveled neither slower nor faster whether it moved with, against, or perpendicular to the Earth; it traveled at the same speed (the speed of light) no matter what experiment was performed.

***

"Einstein’s great insight was to consider the Cheshire Cat-like possibility that the medium does not exist! This was the great insight of special relativity: that light didn’t travel through a medium like other waves, where the motion of the medium (or the motion of the observer relative to the light wave) would change the wave’s speed. Instead, the speed of light itself was the constant, unchanging, universal property, and while a moving observer might see the light’s crests-and-troughs passing them more or less frequently dependent on their motion, the speed of light itself never changed.

"Ten years later, in 1915, Einstein incorporated gravity into the theory of relativity: giving rise to general relativity. Similar to how light is a wave in the electromagnetic field — even though the field itself can have any value, including zero, and even though there’s no medium needed for it to travel through — the gravitational field can have waves in it too: gravitational waves. Once again, as gravitational waves propagate, they can do so:

"...through any gravitational field, including in places where the gravitational field is zero,
and always move at the same speed — the speed of gravity — regardless of the motion of the source or the observer. As with light, there’s no evidence for the existence of a medium that appears in any experiment or observation, even though we’ve now detected hundreds of gravitational waves directly.

***

"Empty space (or spacetime) is certainly “real” in the sense that it exists; it’s where everything in the Universe lives! We’re certain that a medium isn’t necessary, and that if space itself is such a medium, it doesn’t have any of the traditional properties that we associate with any other known medium. All massless waves — light waves, gravitational waves, even gluon waves — travel at the same speed, as the speed of light and the speed of gravity are equal, but whether this is a hint of an underlying medium or just a fact of reality remains undetermined.

***

"It still may be the case that there is a medium, or some type of unknown aether, that truly does underlie all of reality, but if it does, we have no evidence for it. Nature is telling us that we have waves propagating in our Universe without the need for a medium at all: the most mysterious Cheshire Cat we’ve ever encountered."

Comment: space may be empty as far as a medium material is concerned but remember, it is filled with virtual particles according to quantum theory, popping into and out of existence all the time. Obviously God works as a quantum mechanic.