**111 years ago, Albert Einstein proved that there is a theoretical possibility of time travel into the future. Is it only a matter of time until they open a facility to accelerate people into the future or is it just science fiction?**

Author: Alon Halperin, young Galileo

The year is 2135. Somewhere in the Negev, at a secret site, the most secret facility in the world, the "Malal" (the facility for accelerating people into the future) was opened. Lieutenant Colonel A is put in a closed cell that is inside a system of circular and underground tunnels that stretch for many kilometers. The closed cell is slowly accelerated with Lieutenant Colonel A inside the tunnel system, until it reaches very high speeds, which are close to the speed of light (about 300 thousand kilometers per second). After Lieutenant Colonel A moves for some time in the accelerator, he stops the cell, exits the secret facility and discovers that he has reached the future.

Sound like a scene from a science fiction movie? Although we still do not know how and if at all it is possible to accelerate people to such speeds, but this is only a technical problem. If one day physicists and engineers manage to solve this technical problem and build an accelerator of people for high speeds (like the particle accelerator built in Switzerland), it will be the first time machine in history, and whoever is accelerated inside this facility will be able to move in time to the future.

**It is possible? **

In 1905, Albert Einstein, one of the greatest physicists in history, stunned the world when he published the "special theory of relativity", which completely changed humanity's understanding of the behavior of physical time. Einstein discovered this fact: "Time is relative". That is, when moving at high speed, the time that passes for those who move fast is relatively shorter than the time that passes for those who move more slowly or do not move at all.

Although it is difficult to understand how this really happens, this fact has already been tested and verified countless times in many experiments. To try to understand what Einstein revealed to us, let's imagine two people standing side by side and each of them holding a watch. When they look at the clock together, they see that they are moving at the same rate: both are moving at a rate of 60 seconds per minute, and each second is the same as the other, so neither of them can reach the future before the other. At a certain point one of them gets into the spaceship, and moves at a very high speed relative to the other, who remains stationary. Looking at their watch they continue to see that each of them is progressing at a rate of 60 seconds per minute. But the difference is that one second in the spacecraft is not the same as one second on the ground.

Without them noticing it, the second one in the spaceship goes slower than the one on the ground, so when the spaceship stops and they meet again - they will find that the time that passed on the clock on the ground was longer than the time that passed in the spaceship.

sounds strange? This was already tested in an experiment that took place in 1971. An atomic clock (which is a very, very accurate clock) was put on a plane flying at high speed around the earth, while an identical atomic clock remained on the ground. When the plane landed and they compared the clocks, they found that the time elapsed on the clock in the plane was shorter than the time elapsed on the ground.

**The twins paradox**

One of the well-known examples regarding the journey to the future is called the "twin paradox". The story goes like this: one man is sent into space at a speed close to the speed of light and leaves his twin brother on Earth. The journey to space and back lasts, as far as the astronaut twin is concerned, for a period of several years, and then he returns expecting to meet his brother. When he lands on Earth, he discovers to his astonishment that the time that has passed on Earth is much longer than the time that has passed in his spaceship, and now his twin brother is decades older than him.

This thought experiment is a direct result of the special theory of relativity, and stems from the fact that the astronaut brother is moving at a very high speed, so the rate of his time has slowed down greatly from the rate of time of his twin brother on Earth. Therefore, the time spent in the spaceship was shorter than the time that passed on the surface of the Earth (actually the explanation is more complex because speed is also relative: to the same extent that the astronaut moves quickly relative to those who remain on Earth, those who remain on Earth move quickly relative to the astronauts in the spaceship).

** **

**The first passengers on time**

The truth is that today we are already living in time travel. Astronauts who spent a long time in the International Space Station moved in the space station for a long time at high speed around the Earth, so the time that passed for them was shorter than the time that passed on the surface of the Earth.

The world record in time travel to date is the Russian cosmonaut Gennady Padalka, who stayed in orbit around the Earth for a cumulative time of 879 days, and because of this, when he returned to Earth, he remained 0.02 seconds younger than people who spent time on Earth, meaning that time travel had already taken place. If we only know how to increase our speeds very much to close to the speed of light, this leap into the future will increase significantly.

**The grandfather paradox**

If so, travel to the future is physically possible. The question is whether it is also possible to return to the past. As far as we understand the physical world today, a journey into the past is not possible. Unlike a journey to the future, to date no one has proposed a physical solution that would allow a journey to the past.

The possibility of a journey to the past creates paradoxes. That is, situations that are not possible and create insoluble contradictions. The most famous paradox in this context is the "grandfather paradox". The paradox is about a time traveler who chooses to return to the past and prevent the meeting between his grandfather and his grandmother. If his grandparents had not met, the possibility of his father being born and him being born himself would have been prevented. If he is not born he will not be able to go back in time to prevent the meeting between his grandfather and his grandmother. But if the traveler had not been born in time and had not traveled to the past to prevent the meeting, his grandfather and grandmother would have met, his father was born and he too was born to go back in time and prevent the meeting between the grandfather and the grandmother... and God forbid it goes back in an endless loop from which it is logically impossible to get out.

This paradox concerns a particular case, but it is only one version of countless similar scenarios that describe the paradox that arises in the case of an influence on the past and this influence on the development of the known present. Therefore, it is very possible that the theoretical possibility regarding time travel is only valid regarding travel to the future, and not to the past.

**This is your time**

The truth is that the whole time travel discussion is nice, and relevant mainly for the science fiction genre in literature and film. These subjects have ignited the imagination of people since time immemorial. The human desire to break through the limits of life as we know it and go out into the spaces of choice that are not limited by time and space will always accompany us. Maybe one day physics and technology will develop and we can develop time machines for the future or the past and in both directions, and maybe not.

We must continue to search and find the scientific and technological solutions to make these dreams come true. The history of mankind has taught us that reality exceeds all imagination, and only persistence and tenacity will break the mold of the technological and scientific world in which we live.

However, the question of Stephen Hawking, one of the great physicists of today, who asked in his book "A Brief History of Time" this question should pop into our heads: "If time travel is possible, why don't we meet tourists from the future? Is it because a time machine will never be developed or is there another reason?" We still don't have a good answer to this question. Maybe one day you will establish the start-up that will build the first people accelerator, and with it - the first time machine in history.

*** The author is a lecturer and writes a blog on the history and philosophy of understanding reality in science. Graduated from the Cohen Institute for the History and Philosophy of Science at Tel Aviv University. His book "The Web of Time", which deals with the term "time", will soon be published by Mater Publishing. ****www.alonhalperin.com**

**The article was published in the Galileo Young Monthly for curious children. For a gift digital sheet ****Click**

**go through the hole **

**Wormholes - will they allow us time travel? **

According to Einstein's theory of general relativity, time travel is a reasonable possibility. According to this theory, physicists have already sent ions into the future (tiny particles whose electric charge is like that of an electron, but whose mass is greater) by changing the gravitational field in their environment. But so far, technology has not made it possible to do this when it comes to space travel and sending humans to distant planets.

One of the theoretical possibilities for this is the use of a wormhole. A wormhole is like a tunnel in space, in which the laws of physics will be broken and movement in time will occur at a speed higher than the speed of light, creating a "leap through" in space-time (in a system of four dimensions). In truth, it is impossible to move faster than the speed of light, but the intention is that the black worm will allow a kind of shortcut in space-time. This theory is predicted by Einstein's theory of general relativity, from which it follows that wormholes can serve as a passage to the past or the future. According to some researchers, there are wormholes that even connect universes.

But it has never been proven that wormholes do exist, that is, none have been observed. Besides, if wormholes are ever found, they will most likely be very small, and therefore humans and spaceships will not be able to enter them. Besides that, turning the wormhole into a time machine would not be easily possible because when a wormhole is created, one of its ends (or both) would need to be accelerated to the desired location to cause time travel.

According to the physicist Stephen Hawking, apart from traveling to distant planets through a wormhole, it is possible to link two parties to the same place in other times - and thus a spaceship could pass through it into the distant future and its passengers might meet in another era in the history of the Earth.

**Carmit Gilboa - writer and author of the book series "Dan's Destiny" published by Am Oved**

**The article was published in the Galileo Young Monthly for curious children. For a gift digital sheet ****Click**

**More of the topic in Hayadan:**

- More of the topic in Hayadan:
- A summary of the history of time travel
- Does time inside black holes move backwards?
- One watch in two places at the same time
- Was a mirror universe created during the big bang that goes back in time?
- Time in a side view

## Comments

Israel

One picture will show the clocks of both locomotives showing 0. Correct.

I agree with Schertz

Miracles

Not 2 photos - one photo of the 2 watches together as they pass each other.

The discount was reached by asking how and why. In our case, the question raised by a rival: the speed of light relative to what?

Einstein's answer, relative to everything, leads directly to the lengthening of time and the contraction of length, even though it is not the only solution next in mind.

Israel

Two - pictures, yes, no problem. But the two pictures are not from the same point... to see the same time in one train, the camera has to be in the middle of the train.

What you said about the planes reinforces what I said: make an assumption and check it.

So-and-so is leaving tomorrow for a certain date (past or future).

He leaves the universe weighing (say) 1000 kg.

He himself weighs 1 kg.

When he lands on the date he requests - the universe he lands in weighs 1001 kg.

And the universe he left now weighs 1 kg less.

This is what the journey back to the future looks like.

And this is how time travel should be shown.

All the above descriptions do not describe time travel, but something else...

Miracles

"This is not true! Your mistake is in the expression "unique moment". In the theory of relativity, a point is a combination of place in time, and a unique moment is a point in space time. There is no way to photograph the 4 watches at the same time.'

I agree with you. That's why I only talked about simultaneously photographing 2 clocks, of locomotive A and locomotive B at the moment of the changeover, which is a unique moment in both systems.

No problem photographing only the 2 locomotive clocks together, right? If you doubt, I will send you a picture..

"In science you don't ask why. Assumptions are made and tested experimentally. They did experiments and you see that time is getting longer.'

So just like that they decided to put atomic clocks on 2 planes and fly them in opposite directions?

Israel

In science they don't ask why. Assumptions are made and tested experimentally. Do experiments and see that the time is getting longer.

Israel

You wrote "since the clocks on each train are synchronized with each other, so at that unique moment all the clocks on both trains show 0. Immediately after that they reset, but on each train the clocks continue to be synchronized."

This is not true! Your mistake is in the expression "unique moment". In the theory of relativity, a point is a combination of place in time, and a unique moment is a point in space time. There is no way to simultaneously photograph the 4 watches.

rival

There is no relation to an external reference system, like the system of the other stars.

Let's stay with the simple problem - the brother flies from planet A to planet B. What breaks the symmetry is that star B is at rest relative to star A but in motion relative to the spacecraft.

rival

The principle of relativity - not even Einstein's, Galileo's - says that there is no moving or resting, only relative movement.

I understand there are 4 types of movement:

1. Rest.

2. Relative motion.

3. Acceleration.

4. The speed of light.

Miracles

There is a difference between sync and reset.

A synchronized clock system - a train for example - can stay synchronized forever.

If the locomotive on train A or even one of the cars passes by train B and a high-resolution camera captures the times of the clocks in both systems together, the image will show different times or the same time on the locomotives.

If the times in the picture are the same - for example 0 - the clocks are reset, but only for the moment of the suit.

Since in each train the clocks are synchronized with each other, so at that unique moment all the clocks in both trains show 0. Immediately after that they are reset, but in each train the clocks continue to be synchronized.

But we still haven't answered the main question: Why does time dilation even exist in inertial systems?

It seems to me that I have begun to understand, that is, in relation to the entire surrounding space (the galaxies, the stars) only the spaceship moves, while the planet and on it the brother who stays at home remain stationary.

Israel

I think I agree with you. You say that after the fireplace in the spaceship, at the same distance as between the planets, there is another spaceship. Now the situation is really symmetrical. Still, you won't be able to synchronize the clocks so that everyone sees 0 on all clocks.

"Regarding the observer in train A, the collector clock of B is not synchronized. The same, regarding a viewer of the second train locomotive.

Bozmanism in one axis system does not require bozmanism in another axis system.'

I am not claiming anything else. I was just trying to show that symmetry also exists in the twin paradox. You can see this in the example of the trains.

If we take only one locomotive of them (the traveling twin) that passes the opposite locomotive (the remaining twin) when the time in both is 0, one can ask why when it passes the opposite collector (the distant planet), its time is lower than the collector's time. Where is the symmetry?

But when you add all the trains of which the locomotives and wagons are only a part, the picture balances out and the symmetry is revealed.

Israel

As for the viewer of train A's locomotive, B's collector's clock is not synchronized. The same, regarding a viewer of the second train locomotive.

Balance in one axis system does not require balance in another axis system.

Try to understand the example I gave. Do you agree with what I wrote? If not, where do you think I am wrong?

"So that's it, no."

no what? How are the flashes related to what I wrote?

1. Can't you synchronize the A train clocks between them?

2. Can't you synchronize the train B clocks between them?

3. Can't you direct that the moment the locomotives match each other that their weights will show 0?

4. Doesn't it follow from the above that all the clocks on both trains show 0 at the time of the shift?

5. Won't every locomotive in every train see the clocks passing by as increasing times from its own time? (Each car will also see increasing times in the passing cars, but not necessarily greater than its time).

6. Doesn't this answer the question of an opponent's asymmetry? (Although this does not explain why the time differences are created and also grow and go, that is a separate question).

Israel

So that's it, no. Let's stick with the example of two planets, A and B, and a spacecraft. The spacecraft moves at gamma = 7 (that is, 99% of the speed of light) and the distance between the planets is 14 light seconds. The orbit of the spaceship goes through A and then B.

For simplicity, let's assume the spaceship is far away.

To synchronize between A and B we put a flash in the middle, between the two planets. Every planet gets addicted to the flash, and flashes itself.

If the spacecraft is slow then it will see the flashes from the planets 14 seconds apart (approximately).

What happens when the spacecraft is fast?

Light approaches B at speed c, and B approaches light at speed 0.99c. Instead of 7 seconds, only about 3.5 seconds will pass as far as the spacecraft is concerned.

A moves away from the light at a speed of 0.99c so the relative speed is only 0.01c. Light will take 3500 seconds to reach A.1

Now, this is also true at the moment the spaceship crosses A, therefore also at the moment of your synchronization - the spaceship will see a time difference between the planets.

Miracles

"When the two brothers pass each other, all the clocks show 0". So here's the problem - the clocks on the train are synchronized in the train system but not in the planet system.'

True, they don't.

This is a momentary reset that changes immediately after the suit. There is no problem synchronizing the A train clocks with each other and the B clocks with each other, right? So what's the problem with directing that if the trains pass each other, then the moment the locomotives cross each other both will see 0? And if the locomotives show 0, so do the other train clocks, right?

So at this particular moment all the clocks in both trains show 0. Immediately after that it changes: each locomotive passes clocks in the opposite train that show a higher time than its own as it moves forward.

Israel

You wrote "When the two brothers pass each other, all the clocks show 0". So here is the problem - the clocks on the train are synchronized in the train system but not in the planet system.

Everyone and their mother tongue…..

rival

If you fly at a speed of 1000 km/h from Los Angeles to New York, then New York flies to you at the same speed but in the opposite direction.

If you left Los Angeles at 12 noon Los Angeles time, you will meet New York at 8 pm New York time.

If New York left for you at 12 noon New York time, she will meet you at 2 pm Los Angeles time.

So where is the symmetry?

This means: clock synchronization.

"What you just explained is clear, although I don't understand why this example needs to be complicated with a gamma speed of 10, you would say that it flies at the speed of light and that's the end of the matter.

What is still not clear to me is the original question I asked, why would the brother who flew in the spaceship stay young? After all, from his point of view, he is the one who stayed with the spaceship in place and the planet with his brothers on it are the ones who flew away from him at the speed of light, so why didn't the brother who stayed at home stay young?'

Not the speed of light - almost..

To see the symmetry in the case you brought, it is said that the younger brother is dragging behind him a train 10 light years long whose clocks are synchronized between them but not with the brother at home.

When the two brothers pass each other, all clocks show 0.

The traveling brother will meet the distant planet in one year according to his clock and 10 years according to the planet clock.

The remaining brother will meet the last chariot in a time of one year according to his clock and 10 years according to the clock of the chariot.

Symmetrical enough?

Earth moved away. And no - she moved away. Speak Hebrew in a flash! And why aren't the comments published, the budget is over?

rival

As far as the spacecraft was concerned, Earth was only one light year away. Why? Because the spacecraft is flying to planet B which is, in its axis system, one light year away.

Therefore the situation is not symmetrical.

Miracles,

What you just explained is clear, although I don't understand why this example needs to be complicated with a gamma speed of 10, you would say that it flies at the speed of light and that's the end of the matter.

What is still not clear to me is the original question I asked, why would the brother who flew in the spaceship stay young? After all, from his point of view, he is the one who stayed with the spaceship in place and the planet with his brothers on it are the ones who flew away from him at the speed of light, so why didn't the brother who stayed at home stay young?

rival

Einstein was right and the answer is: everything is relative.

That is, relative to what.

In relation to the Earth - the twin in the spaceship accelerates and moves away. And the twin in the country - its speed as the speed of rotation as DHA. That is, lower. And so the time of the twin in the spaceship works differently from the twin's clock on Earth.

The paradox is - how do times work in different ways when time is equal everywhere? This is the paradox. And there is no answer to that yet.

There are hypotheses such as: "time is flexible" and all kinds of such and so on..

rival

Einstein was right and the answer is: everything is relative.

That is, relative to what.

In relation to the Earth - the twin in the spaceship accelerates and moves away. And the twin in the country - its speed as the speed of rotation as DHA. That is, lower. And so the time of the twin in the spaceship works differently from the twin's clock on Earth.

The paradox is - how do times work in different ways when time is equal everywhere? This is the paradox. And there is no answer to that yet.

There are hypotheses such as: "time is flexible" and all kinds of such and so on..

rival

Let's go back to the example I gave - one brother came from afar in a spaceship. The distance between two planets is 10 light years (this is the distance each planet sees the other).

The spaceship flies at a speed of gamma=10.

In the first planet crossing the two brothers are the same age. They are at the same point and time and each sees himself and his brother at the age of 20 (for example).

As far as the brother on the planet is concerned, it will take about 10 years until the spacecraft reaches the second planet and he will see himself 10 years older.

As far as the brother in the spacecraft is concerned, the distance is only a light year, and it will take him about a year to reach it. He will see himself as one year older.

Miracles,

"Let's take another case - that the brother comes from afar in a spaceship and crosses the earth. Let's assume that by some miracle they are the same age at the moment of the suit. After a while each brother looks at his brother - and sees him younger.

Something is not clear now?'

I did not ask how each brother would see the other, I asked what each brother would see when he looked at himself in the mirror, would he see a 20 year old man? Or a 40-year-old man?

Shapiro,

"The spaceship moves towards the planet at exactly the same speed as the planet moves towards the spaceship"

And that's what I don't understand, why only one of them gets old and the other stays young? Why is there no symmetry?

"As for the spacecraft, the distance between the planets depends on its speed, and therefore also the flight time between them."

The spacecraft is moving toward the planet at exactly the same speed as the planet is moving toward the spacecraft.

And both also started at the same time: 0.

So what's the difference? Why does the spacecraft see the planet at a distance of a light year and the planet the spacecraft at a distance of 10?

Israel

Yes - it's a great experiment.

I thought I explained why there is no symmetry: we have two planets with a distance of ten light years between them, therefore the person on the planet who sees the spaceship is traveling ten light years, and it does not matter what its speed is or what planet he is on. Regarding the spacecraft, the distance between the planets depends on its speed, and therefore also the flight time between them.

By the way - today I demonstrated your favorite experiment to the workers: take 2 polarized lenses and place them at 90 degrees. The light is almost completely gone.

Add a polarized lens between them at 45 degrees. The light reappears.

Didn't you try miracles?

Miracles

I'm just formulating the questions to the opponent...

But do you know what the physical explanation for the lack of symmetry is?

"Every brother looks at his brother - and sees him younger."

Looking - how? With a telescope?

You don't need a relationship for that. Everything we see in the telescope is the distant past.

Viewing should be from 0 range, as in the meeting of the twins.

So why is it that when the traveling twin reaches the distant planet and observes it from range 0, he is younger than her? They both moved at the same relative speed and started at time 0, so why is there no symmetry?

Israel

The reason is that the speed of light remains c in all axis systems. The speed of light remains constant because there must be a maximum speed for transferring information, and light has zero rest mass (I tried a little to simplify...).

If you have a lot of "why" questions, you should listen to Feynman's lecture on magnetism again.

rival

Israel said it right - it's all a matter of synchronizing clocks. In the case of the Twin Paradox, the brothers synchronise, so to speak, before take off. The brother flies, comes back and here he is younger than the brother who stayed.

Let's take another case - that the brother comes from afar in a spaceship and crosses the earth. Let's assume that by some miracle they are the same age at the moment of the suit. After a while each brother looks at his brother - and sees him younger.

Something is not clear now?

rival

Every word - Malmilian. Every letter - Ohana.

Miracles

The question is: why. Why as you say: "The spaceship sees the distance between the planets as one light year" while the planet sees the spaceship 10 light years away. After all, both are moving towards each other at the same speed and the time in all 3 bodies is 0?

I know, clock synchronization.. but what is the physical explanation?

Miracles,

"The essential difference is that a paradox is created, so to speak, only when the brother returns home. What is difficult to understand here???'

If you start to lose your patience again and talk in a bad way, then I will continue to talk only with Israel Shapira, you can't talk like that when you get angry every second.

The paradox is that the brother who flies remains 20 years old, while his brother who stays on the home planet ages and becomes 40 years old, right? I understand it right? Is this the paradox?

But according to you, this is the situation in both cases, both when he turns around and returns to the starting point, and also when he doesn't turn around and continues to fly on, so where is the difference you claimed earlier that there is between the two cases?

Israel

Einstein was wrong ….. Another infinite thing is my patience 🙂

I will repeat my explanation again.

Let's take two planets A and B, the distance between them is 10 light years.

A spaceship passes A with a gamma speed equal to 10 in the direction of B.

Clocks A and B are synchronized. The spacecraft synchronizes its time at the moment of crossing A.

Now, the spacecraft sees the distance between the planets as one light year, so it will see last season as about a year at the moment of crossing B. As for the planets - both see the spaceship flying ten light years away, so their clocks will show 10 years as soon as the spaceship crosses B.

The Twin Paradox is a thought experiment in which our spacecraft returns to planet A. This is the paradox... and nothing else.

Shapiro,

You're right, I didn't notice that I wrote the other way around in the question, but if you hadn't written in such brevity and would have written clearly:

1. The brother in the spaceship will be 20 years old, and the other will be 40 years old.

2. The brother in the spaceship will be 20 years old, and the other will be 40 years old.

So it was much more understandable, sometimes you write long scrolls here and sometimes you suddenly skimp on the words.

rival

I really don't understand why this needs to be repeated - the paradox is that after the brother returns he is younger, and it is not clear why the situation is not symmetrical.

I explained why the situation is really not symmetrical - the reason is that the distance traveled by the spacecraft in the moving brother axis system is different from the distance in the remaining brother axis system.

Miracles

The paradox was created even without the return of the traveling brother. Why does his time move more slowly on his way to the distant planet and not the other way around?

To your explanation that the distance is shortened from the point of view of the traveling brother, we can answer: why not the other way around? Why not in terms of the planet opposite? After all, it moves towards the traveling fireplace at the same speed, doesn't it?

rival

I don't understand where the contradiction is.

Reporter:

Nissim and Shapira,

Stay a moment with my example:

1. Let's say that the two brothers are 20 years old and one of them flies in a spaceship that accelerates at time zero to the speed of light, he flies to a planet that is 10 light years away, and as soon as he reaches it he immediately changes direction and returns. Once they meet again, the brother who stayed on the planet will be 40 years old, while the brother who left the spaceship will be 20 years old?

2. Same example, only the brother in the spaceship flies at the speed of light (time zero acceleration) to a planet that is 20 light years away, once he reaches the planet, how old will he be? And how old will his brother who remains on the planet be?

The answer to 1: 40 and 20.

For 2: 20 and 40.

In both cases the traveling brother is the younger one. In 1 you asked first about the rest and in 2 about the traveler, therefore the answers seem opposite.

rival

The essential difference is that a paradox is created, so to speak, only when the brother returns home. What is difficult to understand here???

Shapiro,

"In both cases the traveling brother remains the young man"

So why does Nissim claim that there is a fundamental difference between a situation of returning to the starting point, and between not returning to the starting point?

Shapiro,

Sorry I thought the wording was clear, here is a revised wording I meant:

"1. Let's say that there are two 20-year-old brothers and one of them flies in a spaceship that accelerates to the speed of light at time zero, he flies ***to another planet*** that is 10 light years away, and as soon as he reaches it he immediately changes direction and returns back ****to the home planet from which he came out****. Once they meet again, the brother who stayed on the planet (****home planet****) will be 40 years old, while the brother who left the spaceship will be 20 years old?''

Is this a clearer wording?

rival

Your question was formulated:

rival

"1. Let's say that the two brothers are 20 years old and one of them flies in a spaceship that accelerates at time zero to the speed of light, he flies to a planet that is 10 light years away, and as soon as he reaches it he immediately changes direction and returns. Once they meet again, the brother who stayed on the planet will be 40 years old, while the brother who left the spaceship will be 20 years old?''

There is confusing wording here. What planet did the traveling brother stay on if he turned around as soon as he reached it?

In both cases the traveling brother is the younger one.

Shapiro,

Nissim says that in both cases the brother in the spaceship will stay young and the one who stays at home will grow old, doesn't this contradict the answer you gave me earlier?

1. 40 and 20.

2. 20 and 40.

Israel

Because these are the terms of the question of the opponent himself.

Miracles,

Again, I don't understand your answer, you are telling me that in both cases, both with returning to the same point and without returning, the brother in the spaceship will remain young and the brother who stays at home will age, so what is the difference?

Miracles,

Again, I don't understand your answer, you are telling me that in both cases, both with returning to the same point and without returning, the brother in the spaceship will remain young and the brother who stays at home will age, so what is the difference?

Miracles

"The point is the distance between the two planets. In the planetary system the distance is, say, 10 light years. In the spacecraft system - the distance is …… 0. That's all.'

I suppose an opponent's question would be: why not the other way around?

rival

I repeat: the point is the distance between the two planets. In the planetary system the distance is, say, 10 light years. In the spacecraft system - the distance is …… 0. That's all.

Miracles,

Sorry, I don't understand, what a paradox, you say that in both cases, both with returning to the same point and without returning, the brother in the spaceship will remain young and the brother who stays at home will age.

rival

As long as the brother has not returned home - there is no paradox. A "point" in relativity is a combination of location and time. The paradox (so to speak) was created when the two brothers were at the same point.

It was a miracle…

1. So according to your words in both cases the brother in the spaceship will remain 20 years old and the brother who stays at home will be 40 years old, so why did you first tell me that there is a fundamental difference between returning to the starting point and not returning to the starting point?

2. Pay attention to Israel Shapira's answer, it seems to me that it contradicts your answer.

rival

1 is correct

2 He will still be 20 years old and his brother will be 40 years old.

Shapiro,

Interesting, that is, in the case of a return to the home planet, the brother who flies in the spaceship will remain young and his brother who stays at home will grow old, and without returning home the brother in the spaceship will grow old and his brother who stays at home is the one who will stay young?

Miracles,

1. If the brother flies to a planet that is 10 light years away, and returns back (at the speed of light) when he exits the spaceship and meets his brother, he will be 20 years old and his brother who stays at home will be 40 years old, right?

2. If he flew to a planet 20 light years away, once he got out of the spaceship how old would he be? And how old will his brother who doesn't fly be?

Please answer 1 and 2, it will help me understand.

1. 40 and 20.

2. 20 and 40.

"Not a bit the other way around?"

Yes, on the contrary, note that I immediately sent a correction message.

rival

Pay attention to something - "a planet located 10 light years away". This is the key to understanding!!!

This distance is in the brother system that didn't fly, and only there! Suppose the spaceship is flying at a speed of gamma = 10. So, for the spaceship the distance is only one light year.

Shapiro,

You're just confusing me, why don't you answer clearly? I asked two questions first and you answered 20 and 40, was it an answer to question 1 or to question 2? According to you, in the two cases I gave, the brother who left the spacecraft would be 20 years old and the brother who stayed on the planet would be 40 years old?

Yes or No.

Quick fix..

The answer is, as mentioned, clock synchronization. In order to understand this, one must ask: Why does the time extension take place at all?

This links directly to your previous question:

How do you determine which of the two moves at the speed of light? Relative to what is this speed measured?

"From your answer I understand that in the two cases I gave in my examples, both in case 1 and in case 2, the brother who left the spacecraft would be 40 years old, while the brother who remained on the planet would be 20 years old."

Not a bit the other way around?

Oops correction regarding section 1, the brother who left the spaceship will be 20 years old and the brother who stayed on the planet will be 40 years old.

Shapiro,

1. From your answer I understand that in the two cases I gave in my examples, both in case 1 and in case 2, the brother who left the spaceship would be 40 years old, while the brother who remained on the planet would be 20 years old. How does this fit with Nissim's claim that there is a fundamental difference between returning to the starting point And between a non-return flight to the starting point?

2. If we refer to the second example I gave regarding a flight to a planet 20 light years away, then again we return to my original question, why would the brother in the spaceship stay young and not age? After all, for him (the brother in the spaceship) the planet and his twin brother on it, they are the ones who went on a journey and moved away from it at the speed of light, so why shouldn't they stay young and he will grow old?

rival

1 is correct

2 As Israel said. Note that for the flying brother the distance is 0 and no time passes.

20 and 40.

Nissim and Shapira,

Stay a moment with my example:

1. Let's say that the two brothers are 20 years old and one of them flies in a spaceship that accelerates at time zero to the speed of light, he flies to a planet that is 10 light years away, and as soon as he reaches it he immediately changes direction and returns. Once they meet again, the brother who stayed on the planet will be 40 years old, while the brother who left the spaceship will be 20 years old?

2. Same example, only the brother in the spaceship flies at the speed of light (time zero acceleration) to a planet that is 20 light years away, once he reaches the planet, how old will he be? And how old will his brother who remains on the planet be?

rival

Israel explained that the matter is synchronization.

The example I gave explains why there is supposedly a paradox. Is it understandable enough?

Suppose a spaceship passes the earth at the speed of light, and clocks are synchronized at the moment of the shift. After a certain time, if each brother looks at his brother he will see him younger. But - this is not the case in the twin paradox. It's a completely different situation. Returning to the starting point creates a substantial difference (regardless of accelerations).

Differentiate between the two cases and you will see that both are clear.

rival

The key to solving the twin paradox and the whole issue of time dilation is clock synchronization.

You can see this in the following example:

You have 3 spaceships at rest on a straight line with a light year distance between each two.

At a certain stage, spaceships 1 and 2 accelerate towards 3 until they reach a constant speed of about 0.995C with a gamma factor equal to 10.

They synchronize their watches and wait patiently for 2 to pass 3.

When 2 and 3 pass each other, the time in the clocks of all spacecraft is 0.

What will happen when 1 and 3 meet? Which clock will be faster relative to the latter?

If the acceleration was the determining factor, clock 1 would be behind because it accelerated and clock 3 would not.

But according to relativity, clock 3 is the one that will lag behind clock 1.

So how does it happen? And how is it that 3 can also call 1 and 2 a retarded couple?

This means: clock synchronization.

Correction, in terms of the brother in the planet spacecraft and his twin brother on it, they are the ones who went on a journey and moved away from it at the speed of light...

Miracles,

Thanks for the answer but it confused me a bit.

Let's talk about a journey in one direction only with no return, one of the brothers goes on a journey at the speed of light (or very close to the speed of light) no matter which direction, and we will neglect the acceleration, let's say that after a few seconds or after a few minutes he is already moving at maximum speed.

After 30 years (according to the clock of the brother who remained on the planet) they both look in the mirror, which of them will see in the mirror a 20-year-old person, and which of them will see a 50-year-old? why? Why would the brother on the planet see the reflection of a 50-year-old man in the mirror? After all, as far as he is concerned, the planet and his twin brother on it are the ones who set out on a journey and moved away from him at the speed of light...

So again, how do you decide which of the two brothers moves at the speed of light? Relative to what is speed measured?

rival

You made an important point. The phenomenon happens regardless of acceleration. The phenomenon is due to the speed only.

Look at it this way: the twin's journey is to a star 10 light years away. Let's assume that the speed is very close to the speed of light, and that the time/distance shortening factor is 10. Let's assume that the acceleration time is very short, and we'll neglect it.

For the remaining twin - his brother flew to a distance of 10 light years and back, and the passing time is 20 years.

For the flying twin - the distance shortens, after the acceleration, to one light year, and it will take a year to reach it. After he changes direction, the distance to Earth will be about one light year, and it will take him another year to return.

The brother who stays will mature in 20 years and the one who flies will mature in two years.

I have a question, let's say there are two identical 20-year-old twins, one of them stays in place and the other goes on a 30-year journey at a speed of 99% of the speed of light, and let's say that the acceleration time is really negligible, that is, a few seconds after the start of the journey it is already at maximum speed and no G forces.

Why is it that after 30 years it seems that the brother who stayed in his place has aged 30 years (ie he is now 50 years old) while the brother who went on the journey is still 20 years old? After all, as far as the brother who went on the journey (after he had already finished accelerating) is the other brother who is moving away from him at the speed of light... so why won't he (the brother who stayed on the home planet) stay young while the brother in the spaceship will grow old? How do you determine which of the two moves at the speed of light? Relative to what is this speed measured?

I hope the question is clear.

A. Ben-Ner

The meeting between the twins happens in the future of both of them. The one who returns sees his brother older than he was at the time of launch. The twin "paradox" is of course not a paradox, and it is an easily measurable phenomenon.

It seems to me that there are two logical errors in the article.

I will try to argue briefly:

A]. If the time measured by the first twin, (the one that travels at a speed close to the speed of light) is shorter than the time measured by the second twin, then from the point of view of the second twin, the first twin did not travel to the future but to the past, just as, from the perspective of us, KDA people, cosmonaut Gennady Padalka traveled back in time at a rate of 0.02 yrs.

B]. Hawking's question is also unclear.

On the one hand he maintains that traveling back in time is not possible, on the other hand he asks why we don't meet tourists from the future? And if it weren't for tourists from the future, the journey to us is a journey back in time, and this is not possible.

So where is the paradox for him?

Nice math exercise:

What should be the radius of the circle in which deputy A will rotate at, say, 90% of the speed of light and be acted upon by, say, one g. (Obviously we're talking about a spaceship. On Earth, even with the orbit circling the entire planet, it won't be enough)

I think what confused him is that they say that in a quantum computer an immediate collapse is made to the desired answer at the moment of measurement.

The truth is that everyone has already time traveled to the future without even knowing it

It is enough to go to a higher floor to travel in time

rival

What does it even mean "calculation at the speed of light?" The computer isn't going anywhere...

Orty,

I see that miracles preceded me, who told you that a quantum computer can calculate faster than the speed of light? How did you get to that?

Orty

When the first sentence of your response is meaningless - is there even any point in reading the rest of the response?

A quantum computer can calculate at a speed faster than the speed of light, and according to theories about anti-time it is even possible to observe quantum action occurring simultaneously in the entanglement. I went with the topic of anti-time to the protocol of a logical operation that a computer can perform and wrote the theoretical time machine. The idea for the "machine" was made after meditating on the topic "What do we want from time and is it possible to beat it?" I came to the conclusion that it would be possible to warp time under very far-reaching conditions and then I characterized those conditions on human behavior. The question I asked myself at the end of the exercise is whether a personal message, which touches the personal time horizon, in a scenario in which the message is received and in a scenario in which it is not, will affect my happiness and will my happiness cancel the existence of the time machine? The limited loop is the possibility of receiving a message from the future. So I wrote a script with Uri Hadad and we produced a short version of a crazy scenario... the short film won Cal-Tech 2015. It was directed by Itai Cohen. I would be happy if you had an opinion about my time machine: http://ortis78.wixsite.com/timelineprotection Orty

Why was my response from yesterday not published?

The scenario at the beginning of the article does not take into account the enormous centripetal force that will be exerted on Lt. Col. A... a living person did not get out of that cell.

Time travel to the future with no possibility of return, is no different in terms of usability

In "simple" cryonics (freezing), which they also do not know how to perform properly...

After all, the time on earth will in any case pass at the same rate and with it all

The risks that the machine will not survive - and if there is no interaction with whoever is there

In the future (which requires some time travel) - there is no difference in terms of usability.

The difference is that practical human cryonics is seemingly imminent

More to do than the journey to the future by other means and the

The "passengers frozen in time" can be thawed whenever you want....

And in Hebrew: Habel”XNUMX!

Regarding the delusional scenario at the beginning of the article, just forget to take into account the enormous centripetal force that will act on Lieutenant A, which will create such a tremendous G-force that it will simply crush him into something unrecognizable, a living person did not get out of that cell.