Hi Giovanni
I read your interesting and thought-provoking essay. I have some comments and doubts about some issues that I would be grateful if you could make some comments. You mention that:
But in some sense we never actually "see" spacetime, we never "detect spacetime", and over the last century we gradually came to appreciate that there would be no spacetime without particles.
You argue against space-time, but it was not clear to me what new conceptual framework or formulation you propose to replace space-time. For instance, in thermodynamics time is not an indispensable item for the calculation of the physical quantities, by only knowing the pressure, the temperature and the volume one can predict the outcome of a system no matter how much time elapses. To be honest, I did not get well why you see space-time redundant, the arguments you lay down appear to me somewhat messy, in what sense you think they are redundant?
On the other hand, I have been studying the problems of the measurement of the one-way speed of light and of clock synchronization and one of your statements call my attention particularly this: "Alice and Bob establish that they are in relative rest at a distance L with synchronized clocks."
According to my research the one-way speed of light has been never measured and clock synchronization a la Einstein assumes that the one-speed of light is isotropic which turns out to be redundant and thus a dead end. I have realized that clock synchronization has become a non-trivial task as at first sight it may seem.
Moreover, you mentioned in relation to the aether that:
I shall leave these questions to the appetites of philosophers... And then quote Poincaré:...Whether the ether exists or not matters little - let us leave that to the metaphysicians... Later you argue that the concept was rule out from physics because it turned out to be useless.
However, in my essay I hold the opposite opinion that reviving the aether it is more useful to solve most of the present problems of physics. Bell, Dirac and others contented that the situation of the aether in 1905-1915 was quite different from the situation of the aether in the middle of the XX century. This seems to me very plausible and I discuss in my essay some of the misconceptions around this concept. I claim that certain assumptions should be revived in physics because of their usefulness. One case of this was the notion of light as a particle brought back to life by Einstein. I would like to quote what Newton thought about the aether and its connection with gravity (Vesselin Petkov also holds that gravity is not a force and thus quantization of gravity is chimera), which I think it could be of great relevance to physics:
"Gravity is the result of a condensation causing a flow of ether with a corresponding thinning of the ether density associated with the increased velocity of flow..."
To make even clearer that Newton was actually Cartesian in the philosophical matters of gravity, in a letter to Bentley in 1692 Newton wrote:
"It is inconceivable that inanimate brute matter should, without the mediation of something else which is not material, operate upon and affect other matter, without mutual contact, as it must do if gravitation in the sense of Epicurus be essential and inherent in it. And this is one reason why I desired you would not ascribe 'innate gravity' to me. That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance, through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an ABSURDITY, that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it."
Making the assumption that the quantum vacuum is some sort of fluid (as the CERN experiments have revealed) it has been shown that the bending of light due to the presence of a massive object can be equivalently explained by a gradient in the refractive index of the vacuum.
Finally you mention that:
But how should one describe the position of the particle when it is formally "inside" the barrier? And especially how much time does it take a particle to quantum-tunnel through a barrier?
Besides reconsidering the aether in physics one should get rid of the notion of particle. Instead, I propose to use solitons which, as it is well known in several field of mathematics and physics, behave as particles in all aspects. The essay of Jarek Duda explains all the similitudes and at the same time the advantages of dealing with solitions in physics instead of particles. If one incorporates these two ingredients into physics the wave-particle duality disappears and experiments such as the double-slit experiment become quite intuitive and easy to handle.
I wish you good luck in the contest and I would be grateful if you could leave me some comments about my essay.
Israel
