Parallel universes, or alternative universes or mirror universes have had a long run of popularity in science fiction and science fantasy, in both print and visual formats. One need only look at an “Alice
Continued from yesterday’s blog…
But there’s also a second catch – and here’s where parallel universes enter the picture. To avoid all those time travel paradoxes sci-fi writers love so well, if you travel back in time you also have to travel between parallel universes!
By all means go back to early April 1912 (I’m ignoring Catch #1 for sake of illustration here) and warn the Captain of RMS Titanic of what’s going to shortly happen. Assuming you convince him of the pending disaster (but more likely as not you’ll be thrown straight into the loony bin), and the disaster is avoided, you’ll have saved the ship and passengers and crew in a parallel universe – not in our Universe. Our RMS Titanic sank. People died. That cannot be changed, at least not by anyone from our Universe.
Because parallel universes don’t have to be carbon copies of ours, you might find, of course, that the ship maybe known as HMS Titan, and she’ll be due to strike a mine instead of a iceberg because the First World War started a decade earlier in that universe.
Maybe one could go back and warn parallel dinosaurs that a parallel asteroid was coming – only I doubt they’d listen (unless of course in this parallel universe they had evolved both an intelligence and technology to deal with the issue).
Or, by all means go back to 1912 and meet (and chat up) your now young and future great grandmother (or great grandfather as the case may be). You both fall in love and get married and thus your real great grandparents never meet and therefore one of your grandparents never was born and thus one of your parents never made it into this world and thus neither did you. So how can you exist therefore to have gone back in time and meet your great grandparent? (Note that this is a more humane version of the grandfather paradox where you kill one of your ancestors before they got their reproductive act together). I assume here that by doing so, that is going back in time and meeting your great grandparent, that you’re not actually going to be able to parent or father or produce your own grandparent, hence parent, hence yourself. You’re not your own great grandparent. Not in this Universe.
If you had done the above in our Universe, you’d have a paradox. You have prevented yourself from being conceived and born. You can’t be your own ancestor. There’s no paradox if you went back to a 1912 in a parallel universe. In that universe you indeed prevented your potential future existence in that universe, but not your actual existence which happened in our Universe.
But maybe you didn’t really travel back in time at all (eliminating Catch #1). If there is such a thing as a universal ‘now’, then our 2012 might correspond to another universe’s 1912 (and our 1912 corresponded to their 1812, and so on). Therefore, that you in our Universe in 2012 can perhaps see the living, albeit ghostly, image of someone/something that exists in that other universe’s 1912 (and maybe vice versa).
Now it doesn’t follow that our Universe of 2012 is actually a century older than a parallel universe whose ‘now’ is 1912. Evolution just developed at an ever so slightly slower pace in our parallel universe – that’s all.
There’s apparently yet another catch in all this. If you do time travel to a parallel universe, whether its real time travel, or pseudo and just apparent time travel, once you go, you’re stuck – there’s no coming home again. Of course you might in turn time travel to a third and fourth, etc. parallel universe, but you can’t come back to our Universe again, for that could mean one universe, our Universe, contains two copies of identical bits of matter – matter (in the form of you) has been created out of apparently nothing, in violation of basic conservation laws.
Why can’t you go home again? You could conceivably return to the time just before you originally left and therefore there would be two identical copies of you existing at the same time and vicinity. Another universe could of course contain more than one copy of you. A universe can lose matter (you) to another parallel universe. A universe therefore can gain matter (you again), but no universe can have more than one copy of identical matter. That doesn’t mean that 50 parallel universes couldn’t lose their own version of you, and all 50 versions of you ends up in say a 51st universe. There are no exact duplications, so no problems.
There’s also what’s known as information paradoxes within time travel scenarios that are also resolved via parallel universes. Say, for example, that your name is Richard Wagner (I’m sure there are lots of people in our 21st Century with that name), and you were named after the famous opera composer. And say, like millions of others, you’re a fan of Wagner’s operatic music and productions, and further say you have the ways and means to travel back in time to the 19th Century and have a desire to meet your famous namesake. And so off you go to meet the young budding opera composer – maybe get his autograph!
Upon arrival in the 19th Century however you find that there is no such person! Well, being a fast thinker ready to seize the moment, you figure you won’t be missed in the 21st Century (you’re an only child, an orphan, unemployed and unmarried). So you decide to step in and fill history’s breach and become somebody famous. You know exactly what to do, and so you become THE Richard Wagner. The operas (which you know so well) are duly composed by you and performed and all’s well with established history and the world – or is it?
The question arises, and remains, where did the operas (music, plots, etc.) actually come from? You learned and eventually knew them by heart when living back in the 21st Century, yet you apparently composed them yourself based on that knowledge in the 19th Century. Something is screwy somewhere. Original opera music and productions have apparently been written and created without any creativity or intellect involved.
Of course there is no paradox if you invoke a parallel universe. In our Universe there really was a 19th Century opera composer known as Richard Wagner, and a 21st Century enthusiast of his music and productions with the same name. The 21st Century Richard Wagner does travel back in time to a 19th Century, but a 19th Century in a universe where the composer Richard Wagner never existed. Our 21st Century fan of Richard Wagner brought our 19th Century’s Wagner’s music to a parallel universe where it hadn’t or wouldn’t otherwise have existed. So, no paradox! There was a point of origin or an original intellect and acts of creativity in our Universe and in our 19th Century.
And by the way, there are dozens of variations on this theme in the literature, especially books that highlight the paradoxes of time travel.
As you see, you can have a lot of fun with proposals that give credibility to parallel universes, which is all the better as these proposals are thoroughly grounded in hard science. Lastly, we need the concept of parallel universes to help keep our beloved sci-fi authors in a profitable job!
Summary: Because time travel is allowable in relativity physics, to avoid time travel paradoxes, one requires parallel universes to exist.
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