If the universe is infinite, shouldn't I already have been contacted by a time and space travelling doppelgänger?

If the universe is infinite, by virtue of chance it means that every possible configuration of matter must exist somewhere (according to this documentary).

Therefore, if the universe is infinite and it's possible to travel through time and space instantaneously, by sheer chance there must be a version of me out there that can do so and that wants to contact me.

Since this has not happened yet, can I conclude that either instantaneous travel through time and space is impossible or that the universe isn't infinite?

On a broader scale: given the infinity of the universe, should certain occurences that occur everywhere at the same time not occur always throughout the universe? Or do such occurences simply not exist?

• My sense is that the hypothesis about near-infinite speeds might need to be revised or discarded... Aug 8, 2012 at 16:23
• @JosephWeissman, In my question it is a premise (however unlikely it may be). Or is that your answer?
– user2215
Aug 8, 2012 at 18:08
• Ok, I have read the replies. In a infinite universe, with infinite matter, all configurations will exist. We are not talking of quantum physics. A infinite universe, with infinite matter implies infinite possibilities.
– user2735
Nov 26, 2012 at 22:09
• If the universe is infinite, and there is a possibility different from zero for us to find ourselves not been contacted by our doppelgänger yet, then that scenario is happening just right now, with 100% of certainty. Assuming that the universe is infinite, implies for sure that doppelgänger exists, and that they have not contacted anyone of us yet, or possible never will do. Nov 27, 2012 at 1:23
• Mere existence is not enough, you are forgetting Time. To be sure you also need: every possible event has happened. Which in turn renders all such questions useless. So if your question is valid, that event has not happened yet.
– user2411
Nov 27, 2012 at 12:22

There is a problem with such a flow of logic. And the answer lays in calculus and limits. (and looking at which infinity is bigger) As well as actually looking what timetravel means.

If universe is infinite and time and space travel is possible for complex matter then there would be beings capable of such travel.

However infinite universe would also mean that there is infinite number of exact copies of earth. One infinity is not equal to another. Moreover if we know that one infinity is twice as big as another we can divide the two and get a finite number (for example if you divide `1+1+1+...` by `2+2+2+...` you get `2`. The probability of you getting visited by a time/space traveling being would be determined by `[number of beings that are capable and want to visit earth]/[number of earths]`. Because most likely time traveling beings are much more complex then humans they will also occur much less often (not to mention the fact that some of them might not want to visit us) so the ratio is going to be less then 1 so the probability is less then one. 1 alien / 100 earths means only `1%` probability.

Unless we assume that each of these aliens would travel to multiple earths in which case it all depends how much effort it takes them to travel to another planet. The loWer the effort the higher the chances of such alien visiting. If its effortless for such an alien and they want to visit everyone probability of us being visited would be `100%` and we already would be visited. But there are always some constrains.

However time and space travel most likely is not possible in all times in the existence of the universe. At the beginning of our universe for example there were no atoms and after that there were no stars. As universe progresses through time there might be strange behaviors as well that prevent time travel or existence of intelligent life. (although I dont trust any of our current models that predict what will happen to the universe as we cant even predict the weather very accurately) This means that it would take some time for time/space traveling beings to evolve and then they would have limited time to travel back in time. (there might be further limitations to time travel which we dont understand)

This means that the time traveling beings dont exist at all times throughout the universe (unless of course they travel there) That decreases the probability of meeting the aliens further because they can time travel to any time but they can come from only one finite time. Its possible that we exist before the time where time traveling aliens are possible to evolve (because evolution takes time).

And you might think that it wouldnt matter because such a being can always time travel back and back and back so in a way he is at multiple places at the same time, but the way we think about time travel would need to change. Because if we simply travel back in time we could change the past so we do not exist and therefore we never travel back in time.

So it would have to mean either that some time travel possibilities are impossible. Or that we create a parallel universe every time they would time travel.

• Thank you, finally a thought through, sensible answer. One thing I am having trouble believing though is that one infinity divided by another can yield a finite answer. Isn't the answer infinity as well, or at least undefined? It is according to this article.. What do you think?
– user2215
Aug 14, 2012 at 10:51
• @Samuel you're having trouble with this because for every 2 in the infinite series of 2's there is an equivalent 1+1 in the infinite series of ones. Aug 14, 2012 at 12:46
• @philosodad, I've read his answer. I'm asking for feedback regarding the article, as it reaches a different conclusion. Please refrain from restating his answer
– user2215
Aug 14, 2012 at 12:50
• @Samuel I didn't restate it. I pointed out why you don't believe it. You don't believe it because it isn't true. Aug 14, 2012 at 13:35
• "Because if we simply travel back in time we could change the past so we do not exist and therefore we never travel back in time." This doesn't follow. We could be able to travel back in time and not be able to change the past... Kage Baker explores this concept in her fiction. Aug 17, 2012 at 16:08

If the universe is infinite, by virtue of chance it means that every possible configuration of matter must exist somewhere

The answer is no, because if the universe contains every possible configuration of matter, then there must be configurations without time travelers, or where they simply have no appeared yet, etc. We could just be in one such configuration.

• But (with an infinite universe as a given) there should be an infinite amount of travellers wanting to visit us (just as there are those who don't want to), travellers who also have the ability to do so (should instantaneous travel though time and space be possible), so by that logic we should be visited by travellers all the time. Since we're not; either the universe isn't infinite, or instantaneous travel is impossible.
– user2215
Aug 8, 2012 at 19:34
• What I mean is that the absence of travellers cannot be explained by the universe containing every possible configuration of matter. If it is a possibility, however small the chance, it will happen in an infinite universe. So therefore, if there is an event that makes it possible for something to occur throughout all places in the universe (like instantaneous travel), then it will happen throughout the universe (compare it to the omnipresence of light), since there is an infinite amount of travellers with this capability.
– user2215
Aug 8, 2012 at 19:38
• If the universe was infinite in the way you describe, then technically all of existence would be a combined mess of infinite matter. Since that's kind of a wild idea, I assumed you meant that the universe was infinite in the sense that there are infinite "timelines" of possibilities. Aug 8, 2012 at 20:05
• Actually, yes sir, it is very necessarily so. An infinite number of people and things infinitely into the future would produce an infinite number of "teleportations" back to the past, which would make any given time infinitely full of infinite things, rendering it one giant entanglement of infinity. Which makes it infinitely silly to think about. :P Aug 8, 2012 at 22:18
• I apologize if you thought I was being rude, it was not my intent. I'm not sure what grammatical correction you're referring to, and I was talking about the silliness of my own conclusion: "an infinite entanglement of infinity", which seems silly to think about because it's so conceptually beyond our/my grasp. Yes, I'm critiquing your premises as if they are true. If the universe is infinite (in the way you describe) and if it's possible to travel through space/time, then X. My previous comment simply shows what conclusion would actually follow from the those (presuming they're true). Aug 9, 2012 at 15:43

If the universe is infinite, by virtue of chance it means that every possible configuration of matter must exist somewhere ....

From scientists perspective this sentence contains two assertions which are either questionable or outright wrong.

Infinity of the universe: In it's current state it's neither infinite in time nor in space. According to the most widely accepted theory (big bang), the universe is about 15 billion years old and about 100 billion light years across. The word on the ultimate fate of the universe is still out. There are two potential outcomes: "big crunch" and "infinite expansion". The deciding factor is the total mass of the universe which we currently don't know with enough precision. In the big crunch scenario the universe has a finite size and a finite life time. The "infinite expansion" would result in infinite time and space, however, after a finite time the universe would be unable to support life and would be pretty boring. Mass and energy would be so diluted that it will be very empty, close to absolute zero Kelvin temperature with the occasional lonely particle flying about.

every possible configuration of matter: That is an obviously wrong assumption. Consider a universe that consists only of a single block of ice but is otherwise infinite in terms of time and space. Nothing would ever happen: the block of ice would stay this way forever and the only configuration of matter that ever existed. With time the number of possible states grows much faster than the number of actual states that the universe can take. Hence every individual state becomes less and less probable. Here is a simple thermodynamic example: The room that you are currently in is smoothly filled with air. However, the only thing responsible for the distribution of the air molecules is probability: it is perfectly valid state for all air molecules to be in one half of the room (leaving you to suffocate in the other :-)). However, it's very unlikely. Actually the probability is so small that it cant't be expressed in regular scientific notation and one has to resort to something like the Googolplex. Now in order to observe the event "room half empty" you would have to wait trillions*trillions*trillions ... times the age of the universe and during all this time you need to keep the room complete stable and unchanged. This will not happen.

Finally, your scenario also assumes that time travelling is possible, which at least according to special and general relativity it isn't (and will never be).

If the universe is infinite, by virtue of chance it means that every possible configuration of matter must exist somewhere

That's only correct if the universe is infinite and the configuration of the universe is driven purely by chance. There's still the possibility that the universe is finite, or that the universe if infinite, but ordered in a non-random manner.

Therefore, if the universe is infinite and it's possible to travel through time and space instantaneously, by sheer chance there must be a version of me out there that can do so and that wants to contact me.

Now you are adding a new proposition: that of instantaneous travel.

Since this has not happened yet, can I conclude that either instantaneous travel through time and space is impossible or that the universe isn't infinite?

Or that the universe is not ordered in a random manner. At least one of those three hypotheses has to fail.

Fortunately, that's not a problem; there's no particular scientific evidence leading one to believe that these things are true.

• "Fortunately, that's not a problem; there's no particular scientific evidence leading one to believe that these things are true.". First of all, thanks for your response. And second of all; I realize that my conclusion isn't particularly groundbreaking. It was merely fascinating to me that a concept like infinity can be logically applied to draw certain conclusions about our universe (however superficial those conclusions may be).
– user2215
Aug 14, 2012 at 11:16

Therefore, if the universe is infinite and it's possible to travel through time and space near-instantaneously, by sheer chance there must be a version of me out there that can do so and that wants to contact me.

I think there's a central problem with this conclusion, which is that there are actually two conclusions you reach. One is that there are infinite doppelgängers with the power to contact their doppelgängers. The other is that because of the first conclusion, there are no doppelgängers which are not contacted by at least one doppelgänger. Neither conclusion actually follows from the premise.

The second conclusion actually contradicts your premise. If every possible thing that can happen does happen, then somewhere, there is a lonely doppelgänger who is never contacted by his fellows. If that's the case, we can safely assume that you're the you that no doppelganger wants to contact.

Or to put it another way, if I accept your premise, somewhere there is a doppelgänger of you putting a question on a version of StackExchange about whether there is a doppelgänger of itself that hasn't made contact with any of its doppelgängers.

Of course, there's no need to feel bad about being this lonely doppelgänger, since everything that can happen happens an infinite number of times, there are an infinity of lonely doppelgängers to fail to keep you company.

The first conclusion only follows from the premise if the probability that you exist is finite. However, it may not be finite, and instead be infinitesimal. If that's the case, there may be a finite number (even only one) of you, even in an infinite universe in which everything possible happens. I tend to think this is more likely than not, because there may be an uncountably infinite number of possible evolutionary paths.

The first conclusion is also vulnerable to the finite nature of time. It takes time for things to happen in. So it is possible that while it is possible to travel instantaneously, no species ever figures it out because they don't last long enough, in which case no doppelgänger of you ever has time travel.

The first conclusion is also vulnerable to uncertainty about what is possible. There is no civilization of spacefaring proto-lemurs anywhere in the universe because such a thing is simply impossible: to design and operate spaceships, you need a different mental toolkit than a lemur has. So the configurations of matter are not determined solely by random chance, it is random chance plus the laws of physics, which yields the laws of chemistry, biology, etc. The fact that lemurs can't build spaceships doesn't make spaceships impossible, it just makes them impossible for lemurs.

It is possible that a species that develops time travel has necessarily evolved biological structures which we lack, in which case there is no doppelgänger of you that has time travel, but time travel is still possible.

In conclusion, the only thing that you can conclude from the fact that you haven't been contacted by a time-travelling you-doppelgänger is that as far as you know you haven't.

• 1."However, the universe itself is not infinite, the time between the birth and heat death of the universe is finite.", you're talking about time, I'm talking about space.
– user2215
Aug 8, 2012 at 18:12
• 2. "Yeah, but you're the you that the doppelganger doesn't want to contact.", you're forgetting that in infinite space this is impossible. If there is a chance (however unlikely), it will happen in an infinite universe. For either infinity in terms of space or in terms of time, the results are the same (en.wikipedia.org/wiki/Infinite_monkey_theorem).
– user2215
Aug 8, 2012 at 18:13
• @Samuel you don't understand. In an infinite universe, if all things are possible, then there is a you who would be contacted and a you who would not, because otherwise all things would not be possible and you would be denying your own premise. And time and space are just dimensions. If the universe is not of infinite reach in all dimensions, it isn't infinitely infinite and all things don't have to be possible. Aug 8, 2012 at 22:24
• I have to disagree. I know time and space are dimensions, but as you'll see in the infinite monkey theorem, either infinity in space or time is enough (i.e.: one monkey typing infinitely long, or an infinite number of monkeys typing for a set time yield the same results).
– user2215
Aug 9, 2012 at 6:22
• "one monkey typing infinitely long, or an infinite number of monkeys typing for a set time yield the same results" Not true. The length of time the monkeys type has to equal the length of time that it takes a monkey to type a given string, or that string cannot appear. I.E., an infinite number of monkeys typing for 2 hours cannot produce the works of Shakespeare, because it takes longer than two hours for a monkey to hit a keyboard that many times. Aug 9, 2012 at 15:17

If the universe is infinite, and there is a possibility different from zero for us to find ourselves not being contacted yet by our doppelgänger, then that scenario is happening just right now, with 100% of certainty.

Thus, assuming that the universe is infinite, implies for sure that doppelgänger exist, and that they have not contacted anyone of us yet, or possible will never do.

On the other side...

If the universe is finite, there is still a chance for them to exist and not to have visited us yet.

So, you can't tell whether the universe is infinite or finite, based merely on the posibility of the existence of a doppelgänger, that has not visited us yet.

The premise that the universe is infinite does not imply the premise that instantanious time or space travel is possible or communication between multiverses is possible. Neither does is imply that there exists another version of us, an alternate version yes and the two should not be expressed as the same. Another point can also be argued that in a universe of infinite possibilities there exists an infinite number of universes that are independent to an infinite universe.

In mathematical logic there are different forms of infinite. The idea of infinite cannot be argued unless some sort of restrictions are set. ex. Infinite with repetition or without, both can exits independent of each other, both can exist in a general sense of the idea infinite.

I feel that this discussion requires some sort of restrictions to narrow the thought determine how our universe can potentially be unbound, infinite and still give answer to our observations within it. After all in a geneal sence of infinite there has to exist a situation were we never meet out "Doppelgänger" and therefore to make a determination that out universe is not infinite because of this is a logical falsity.

• +1 I just recently had a question assuming the possibility of instantanious time or space travel... Dec 19, 2013 at 23:39