(My)…….limit of accessibility
A result is visible, the so-called Postreiter is or better was in past times a so-called information mediator. The distance he covered, namely the 300 km/day, he was able to transmit a message in three days to a contact person 900 km away. Up to then he is thus and that cannot be changed clearly behind the
reachability horizon. The longer one waits, the larger becomes the area with which one can communicate. I show the division of our world into reachable and unreachable areas in the following picture.
This division depends, of course, on the speed of the messenger – the faster he is, the further we can penetrate into the space in the given time.
Let’s take a look at the means of transport available to us today, they take us to our destination in hours instead of days, weeks or months. Further, we have, as said with the Skat, thus something in the „hind hand“. The journey from Europe to the Far East, which took several weeks a hundred years ago, does not take ten hours today. And if it is only a matter of establishing a connection with the „other side of the mountains“, today the telephone and radio can do it almost immediately.
The following statement is therefore sustainable :
the time distance in communication with distant regions thus depends only on how fast we can send signals there or receive them from there !
I say therefore, dIe most important realization in our understanding of nature was the first step that there is also for the speed of the information transmission a limit, the finite „speed of light“. Only we feel little of it on the earth.
The resulting delay is mostly to be called insignificant and also hardly affects the communication on intercontinental level. Only what happens with us here and today, that distant worlds will experience only later, and what is transmitted to us by them, is just their past. Because the light of the stars, which we see today, has already been radiated millions of years ago from there. We cannot know whether these stars exist now, thus there still, and if yes the following question arises, where they are now. Accordingly, there are already horizons behind which we cannot penetrate in no case.
But even these horizons are still largely determined by ourselves. Because if we could wait long enough, the light of distant stars would reach us after all, and as we have made a reachability diagram for the post rider, so we can do the same for radio signals which propagate with light speed. Only it must be mentioned, of course, what took days for the post rider, the light brings in fractions of seconds. There is a difference in the speed of transmission. Let us consider it. A new, a quite essential aspect still comes into play. In the case of the post rider the horizon could be extended, by a faster horse or more frequent change, later by the use even of motor vehicles. Speed of light however remains speed of light – we have reached an absolute limit there. The propagation of the light defines the space-time horizon, determined by the light cone in space and time. Please remember: What lies beyond this horizon, that is unreachable for us.
In astronomical dimensions, in the space, the areas in space and time inaccessible for us grow of course enormously. A star that is a hundred light years away cannot send a signal today that we will receive in our lifetime, and it will not hear anything from us in that time period either. But this is our personal problem; in sufficiently distant future our descendants can receive quite the signal sent today by said star. With radio waves, thus with light as the fastest transmission possibility, a new accessibility diagram is created in this way.
The light cone determines for us what we can influence in the future, it defines our space time horizon. What lies outside the light cone is in the „beyond“, out of reach for us now. The distant star ∗ lies there today and is out of reach for us. But if we wait long enough – very long for light years distant stars – then it will become visible in our future, we can send it a signal and it us.
The speed of light determines the space-time horizon, which separates for us reachable from unreachable areas.
In physics, on the other hand, absolute boundaries play an essential role today: last horizons, final frontier horizons. They limit the parts of the universe from which no one at our location can ever receive a signal, not even in the far future. How is this possible? This question leads to some of the most amazing phenomena in physics and cosmology today. If we can’t connect with areas of the universe in any way, that must mean that light „from there“ can never reach us. These can only be areas that are far away and also continuously moving further away, or those that do not let out any light. In fact, both forms exist.
How old is the universe? Today’s cosmology assumes a big bang, about 14 billion years ago, in which infinitely hot and dense primordial matter was created, which then expanded, creating our universe. The Big Bang is fixed in time, but not in space; 14 billion years ago, it started everywhere – the primordial world was not a small, hot ball that then exploded, but infinitely dense matter that was then diluted by expansion. Therefore, the time since the Big Bang is not sufficient for a signal to reach us here and now from areas that were sufficiently distant from our starting point at that time. The light from those areas has simply not yet had enough time to make it to us. The world we see is a result of the speed of light and the age of the world. Thus, it seems that we simply have to be patient: In time, more and more of the realm not yet visible to this day will come into our field of vision. The light of distant stars is already „on the way“ into our world.
Only, while we wait, the universe does not keep still. Astronomical observations show that it expands in constantly increasing speed. If this expansion takes place fast enough, there will be stars that will remain eternally beyond our horizon, whose light can never reach us. Even more, stars that we can still see today will be pushed behind our horizon by the expansion – they will be extinguished and disappear for us. Somewhere in distant space there is a horizon behind which we can never penetrate, neither today nor sometime later.
In old fairy tales there is a castle with many rooms; but one of them you must never enter, otherwise you will come to a terrible end. It seems that such rooms also exist in our universe,
Part 3 follows