Mysteries of the Universe 8: and this time the answers of Prof. Elia Leibovitz from "Basher" about the expansion of the universe

This time we dedicate the chapter in the Mysteries of the Universe series to the entire universe and to questions about astrophysics and the answers of senior experts as they appear in one of the best expert sections on the Israeli Internet: the website of the Beshaar association

Hayadan

Direct link to this page: https://www.hayadan.org.il/mystery008.html

The system is intended for use by all teachers and students in the education system. The experts at your disposal are members of "Bashar" - senior academic staff members of higher education institutions in Israel. All respondents work in this framework voluntarily.
At this stage we receive questions in the fields of exact sciences.
The inquiry is made on the Internet using a forum designed for this purpose. The forum administrator categorizes the question and directs it to the appropriate expert. The expert's answer is published in the forum next to the question. You can also receive a notification of receipt of a reply to a private e-mail box.
Questions and answers forum in exact sciences on the Bashar Association website

Let's start with the question of Ohad Meir, a XNUMXth grade student from Ort School in Kiryat Motzkin and the answer of Prof. Elia Leibovich.

the question

"Astronomers determined that the universe is expanding, and is expanding forever, that is, they concluded that the universe is infinite and since the force of friction in space is almost zero, the inertia created in the big bang will last forever.

A theory can be put forward that says the following: from our point of view on Earth, the universe is expanding, but this does not mean that beyond our range of vision there are no bodies that attract the bodies closest to us in such a way that we see them as expanding, when in fact a situation arises in which the universe contracts and does not expand.

The meaning of the theory is that the universe is contracting but beyond our range of vision, so that we are not aware of it, and assume that it is expanding; A conclusion that can be reached from our range of vision, but will refer only to our range of vision and not beyond it.

It is true that the Hubble Space Telescope sees vast distances, but to the best of my knowledge it does not see the whole universe, so it is not possible to come to the conclusion that the above theory is incorrect.

Astronomers' conclusion that the universe is expanding disqualifies this theory without any basis for disqualification (as far as I know).

I would be interested to know if the theory I put forward is possible?"

If so, why did the astronomers rule it out, and if not, why is it not possible?

Answer by: Prof. Elia Leibovitz

You are of course right, fan, in saying that we don't see the whole universe. For this reason astronomers and cosmologists speak of the "horizon" of the universe. This term indicates exactly what the same word indicates in the context of earthly geography. The horizon line is an (imaginary) line beyond which we cannot see anything, so really our knowledge of what exists beyond it is a completely different kind of knowledge. In the astronomical literature you will also find that for the same reason, astronomers really talk, in multiple contexts, not about the universe as a whole but about the "visible universe". This is the piece of space and time from which we, the inhabitants of the earth, are able to receive any signals. It is clear to everyone who is involved in astronomy that the "visible world" is indeed only a small segment of a much larger place. In particular, the "visible world" encompasses only a finite area of ​​space, while today the universe seems to be infinite in its spatial dimensions. It is worth noting that the word "see" is used here in a somewhat borrowed sense. In the cosmological context, we say of an object or factor in the world that it is "visible", if we perceive any radiation, not necessarily light radiation, emitted by that factor.

The claim or belief that the expansion of the universe is a feature that also characterizes it in areas beyond the horizon line is based on the assumption that the physical legality in the regions of the universe that are hidden from us is no different from the legality that prevails in that part of the universe that is visible to us. According to most of the physical theories relevant to cosmology known to us, there is no line or limit beyond which another physics exists. At the same time, it is worth noting that there are modern cosmological theories today, which offer models of the world that are not so far from the spirit of things you propose. According to several such teachings, the universe visible to us is only a fragment of a much wider entity, in other areas of which the behavior of matter and energy is different from that known to us. It is of course difficult to confirm such theories because they describe parts of the universe for which there are no observational findings, and according to the laws of physics known to us today there is no way we will have such observational findings. However, some of these theories are not guesswork in science, as they try to draw possible worlds and reject impossible models, based on a careful analysis of the behavior of the visible world, and based on deep understandings of the fundamental teachings of modern physics, especially relativity and quantum theory.

a question

Prof. Elia Leibovitz also answered the question of Amit Solomon from Kfar Saba, a XNUMXth grader who is waiting for recruitment related to the expansion of the universe.

It is known that the universe expands while creating space-time. Is the speed of its expansion the speed of light?
Because the speed of light is the highest, therefore, if the speed of expansion of the universe is less than it, then the light will "reach" the edge of the universe at some point, and there is no space there... what will happen?
Or maybe the universe expands at a speed higher than the speed of light (doesn't make sense to me), because it expands by the displacement of quantum particles that react with each other, and move above the speed of light?
(If the last idea I presented, speed faster than the speed of light, I didn't explain properly, I'm sorry, but it might help if I say that I meant the behavior of pairs of quantum particles that move together at a speed higher than the speed of light, and by which parapsychological phenomena are now being tried to be explained).
Thanks in advance for any help
Amit

Answer by: Prof. Elia Leibovitz

Peace and blessings to Amit,

According to our current understanding, the expansion of the universe is not a movement of bodies in space. According to Einstein's theory of relativity, the universe is not a tractate of bodies in a given space, but the space itself is an entity that has dynamics. In our universe space itself is expanding. The main source of the distance of galaxies in the universe from each other, in the phenomenon known as "redshift", is not in the movement of galaxies in space but in the constant enlargement of the space separating the galaxies. The difference between the concept of the expansion of the universe that originates from the expansion of space, and expansion that originates from the movement of bodies moving away from each other, can be demonstrated as follows: if we surrounded each galaxy in a kind of giant cosmic balloon, despite the expansion of the universe we would find that the galaxy does not pass through the balloon and it always remains as a closed surface that surrounds The same of all the Hebrews. On the other hand, motion-induced expansion would have resulted in the galaxy at some point entering through the balloon and exiting it. For the sake of accuracy, it should be noted that galaxies also have movement in space, so in the balloon experiment, the galaxy will indeed find itself outside the balloon at some time. However, this movement of the galaxies is not an expansion movement. In this movement, there are galaxies that are moving away from each other, but there are also galaxies that are approaching each other. In recent years, the discoveries of even colliding galaxies have multiplied.
Since the cosmic expansion of space is not movement in the mechanistic sense of the term, it is not subject to the limitation imposed by the theory of relativity on movement in space, whose speed cannot be greater than the speed of light. The amount of space or distance added between two galaxies in the universe depends on their distance from each other. Since the rate is uniform throughout space, the greater the distance between the two galaxies, the greater the amount of space added between them per unit of time. An observer on one galaxy will see the other galaxy moving away at a rate he will call velocity. In his measurements, he will find the rate of receding, or the "speed" (in quotation marks) of the second galaxy, proportional to the distance between the two galaxies. However, the viewer will never see the second galaxy moving away from him at a speed that exceeds the speed of light because the light that transmits the image of the second galaxy to him is subject to the limitation of the theory of relativity.

Yadan astrophysics 1 - the universe

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