June 15, 2012 14:17
Usually, we take it for granted that our past is unchanged. History is always the way we remember it. But how can we know that things are this way? If time travel is possible, then at other times, travelers can always jump back in time and change any of the things on your own. As we will see, is that really the case or not?
We asked several experts for time travel — though none of them, of course, did not make such a trip in person. (And if they did, then keep your secrets to yourself.)
First of all, the fact that changing the past is really difficult to establish, because "it is assumed that when a time traveler alters our past, this immediately leads to a change in our memories of the past, to keep them relevant to this" new "past", says Professor Christian philosophy Vutrich . "If the last change is immediate and completely consistent, that is, include changes in all of our memories and records of the past, then we really can not be sure to note that this has happened."
But according to experts, there are ways by which you can be sure that someone did not change our past constantly.
Time travel is impossible
We have often heard it from many experts. Told Ion Thaler, a professor of physics at the University of Illinois: "The problem is that we do not know how to construct a theory that allows time travel. Without the theory is difficult to say what will be the signs of the phenomena of such a journey. " Thaler wrote a section of time travel to Usenet Physics FAQ, in which he explains that the theory of relativity can allow the existence of "closed time curves" that allow time travel — but the famous "grandfather paradox" (in which you go back in time and kill your grandfather, while he was still a kid) proves that it is impossible. Thaler says, "In short, the" closed time curves "(slang for the physical assumptions, which allows for time travel), seems to be incompatible with quantum mechanics."
Even if time travel is possible, in any case you can not change the past
This view is also very common. Vutrich says that many philosophers of science agree that the past must be consistent in order to avoid multiple time paradoxes. This "restriction consistency" means that there is only one past, and it is fixed. However, an expert on quantum physics Todd Brun said, "Even if you go back to the past with the intent to change the story, he turned so that will force you to take a particular action, rather than to follow your will (and the story will now include a fact of travel time). "
This is the reason why many philosophers time love stories like "All you zombies" by Robert A. Heinlein, in which time is strictly consistent, says Nick Haggett, author of the book: "Always and everywhere travelers in physics and philosophy." Haggett, Professor of Philosophy at the University of Illinois, adds:
To date, we have no understanding of what it means — to change the past. To say that something has changed, means that at one time it was like this, and in another moment — like this, right? And how can you change the past? This must mean that yesterday was the first like this, and then another — but above all, you did not arrive with the time travel in this day and then somehow ended up in there, right? But in this story, you have arrived to this day, so the first option, it turns out, never happened, and the past has changed since your arrival — again, because it does not happen anything different.
The alternative to this view is the assumption that every time you go back in time and change something, you create a new universe, according to the theory of "multiple worlds" Hugh Everett. This new reality will continue to be consistent the past that we will never forget it like that — but it will be the past, which appeared as a result of changes made by the traveler.
Perhaps there are many universes, and change our past causes the universe to share. As strange and scientific and fantastic as it may sound, we should really take this opportunity to quantum mechanics, in which one of the leading interpretations — this is the theory of so-called "multiple worlds" in which each quantum event causes the universe to share. But even in this case, no one can go back and change the history of his own universe.
Perhaps you can go back in time only to the point when it was first invented a time machine
Unless someone has not invented a car, and we just do not know about, then we are safe. Explains the physics professor at Vanderbilt University, Thomas Weyler:
Time travel, if it is possible at all on its own, you can send only to the time of the first time machine. As in the past, our civilization is no time machines, it consistently, while the more advanced civilizations of the past can be changed.
No signs of
The only surefire way to know that time travelers are in our past and change something in it — is if they start bragging about it. That, as a people, they will surely do. Nick says Haggett:
Imagine that tomorrow you come back in time for two days (that is, at last), and makes a dramatic statement on television of today. Thus, today, we will know exactly what you tomorrow influenced past.
And even then we can not be sure that these time travelers to change something, because we remember only one version of the past.
There would be physical traces
Depending on the method of time travel, you may well expect that any physical traces remain, says Haggett. In Carl Sagan's novel "Contact", time travel is possible due to the way in space-time, which leads to the past. According Haggettu, this type of wormhole "requires exotic forms of matter, to keep it open so you can detect." Also in this case is the question of conservation of energy — when you turn up in the past, you are formed of matter and energy, which it was not, and that you actually imported from the future. This can create a trace that can be detect — unless someone will actually go back to our time. That is, in short, the results of time travel will be invisible to those of us who are stuck in linear time, but the methods of travel, perhaps, I will leave some traces.
Games with cause and effect of changing the laws of probability
If anyone can actually go back in time and change it, it can lead to the fact that the investigation will precede causes, says Todd Brun. This in turn may mean that everything goes topsy-turvy leading to a logical contradiction, that we can see. He explains:
Confusion of cause and effect may not be possible in other cases, the event is much more likely. So if we suddenly discover that the events zdravomyslennye violate our probability estimates, it could mean that somewhere there is a time travel. In essence, this means that one can notice the existence of a time machine — perhaps even before it is created. But it is difficult to say what is necessary to pay attention.
History shows that they do not
Let's give the final word of a professor of physics at Harvard University, Gary Feldman: "If the time travelers are constantly changing our past, they seem to do it is not very successful. Why they did not prevent the two horrific and senseless war in the past century? "