As you may know I am an Aerospace Engineer, and I have always been interested with physics, especially relativity theory and quantum mechanics.
In one of my previous posts (here is the link if you have missed it):
I tried a mental experiment where I thought about what the consequences of the disappearance of the sun might be. The first thing was that we would notice the Sun disappearances after approximately 8 min, since this is the time that it takes to light to reach Earth. So let's dig a little bit further on the consequences of this fact.
As I wrote in my previous post the main implication of the fact that light has a finite speed is that what we are looking at in the sky is nothing more than a residual image, it's almost like looking at the past. This has always fascinated scientists and challenged the concept of time, also because it is difficult to define what present, past and future actually are. The concept of time is also mass-dependent because, depending on the distance we are from a certain heavy body, the way we perceive the passage of time changes. This means that if I measured time on the Earth or on a satellite orbiting around it with the same type of clock and I could see the measurements on both at the same time, I would realize that the clock on the satellite is running slower than the one on the Earth. A concrete example of this is the satellite geolocation system (be it the American GPS or the European GNSS), which in order to work properly must measure the time taken by its signal to travel the distance between the receiver (a mobile phone for example) and the satellite itself. By combining the distances of several satellites (at least three), it is possible to geolocalise the subject. One of the main problems to take into account are although relativistic phenomena, since time on the satellite and on Earth are not moving equally, and so there are really complicated algorithms that take this into account.
This concept is even more exaggerated in the proximity of a black hole, that is nothing more than a really high concentration of mass, that has a gravity force so strong that attracts everything towards it. Here, there is a theory called "spaghettification", from the Italian pasta, i.e. Spaghetti, that states that due to the enormous gravitation field that a body would be subjected when being really close to a black hole, and supposing it will not get killed instantaneously by it, his body will start to stretch vertically and compress horizontally, and the time that his head would feel will be completely different from the one of his foots for example (the more near to the black hole the faster the time perceived).
I find this really mind-blowing and fascinating, since even something that we give for granted is not at all like how we think, time is not absolute , but on the contrary is really relative.
Actually the only proof that we have of the forward passage of time, is Entropy. This is the only quantity that gives a sense to the concept of past and future (the concept of present is not meaningful), since we can think about the past as a time where there was less Entropy and the future as a time where there is more Entropy.
An interesting theory that I have read in a book of Carlo Rovelli, The order of time (I strongly suggest it as a reading), states that we consider Entropy as the increase of disorder in the Universe, but this is because we have given a definition to disorder. For him what we call disorder is nothing more than another state of the matter. If I take a deck of cards which was sorted and throw it on the ground, we would say that now we have more disorder, but for him this is actually nothing more than another state of that physical configuration. So, when and if, we will be able to govern all of the laws of physics, even the concept of Entropy which is considered irreversible, will not be anymore, and so the concept of the inverse flow of time will make as much sense as its forward flow does for us now.
What do you think about this? Did you already know about this amazing theories or is this the first time you here about them? If you want, leave some comments and I will more than gladly have a conversation with you on this subject.
