The parallel universe bit is touted all the time by different people. The short story being there are infinite universes existing that almost match another universe. Doesn’t ithe same theory that permits the later, allow for the premise of exact matching universes?
I’m not sure. What’s the scientific basis for it?
And if there are exactly matching universes… what’s the difference? Who cares? I think the idea of multiple different universes is intriguing from a philosophical perspective, but exact copies don’t capture that.
Perhaps, but what does that gain you? So, there’s umpty-ump identical copies of me typing umpty-ump copies of this message to umpty-ump copies of you. So?
In answer to the OP, yes. If there are infinite universes playing out all the possibilities, then there must be infinite universes playing exactly the same choices down to the t. Infinity is a curious thing.
That wouldn’t make any difference to us here in this one, though.
If the premise were true, it would have to be. An almost exactly matching universe at time t would have to be exactly matching at time t -n, where n is not very big. (Or else the universes would diverge, and they wouldn’t match very closely.) Thus, if a universe not very far in the future would match ours not very far in the future, they’d have to match ours today.
That’s assuming the universes started as parallel in the Big Bang. If they diverge, then each universe would spin off others, that would be close soon after the point of divergence, and quickly get further away for the mother universe.
That only follows if there are just a finite number of possibilities.
-FrL-
Why couldn’t they converge, come close to appearing identical, then subsequently diverge?
-FrL-
I don’t see why not, but why do you ask?
-FrL-
That implies that random quantum fluctuations are not truly random but rather determined by some pre-existing condition.
It’s a fallacy to think that infinite is the same as all possibilities. There are an infinite number of even numbers but in that set you’ll never see a single odd number.
my infinity is bigger than yours 
I think that is really the key. One of the only things that we believe are truly random are the behavior of subatomic particles and they exist all over the place. Randomness rather than determinism is built into the universe in a fundamental way. Combine that with chaos theory (small changes will eventually lead to huge diversion) and I can’t see how parallel universes would stay in lock-step with one another. The old ideas about even simple systems with the same fundamental properties resulting in exactly the same outcome has been thrown out time after time. The constraints of the question require that it can’t possibly be true.
It’s an excerise in sideways thinking. All the scifi writers and such like to use the possibility of similar parallel worlds, but nobody I know of has carried that out to the conclusion that it then allows for an exact copy of another universe. I’m checking it here so that somebody else can verify I was thinking correctly. This could led to the testing of an apparatus that shifted you to another universe. You then find everything is exactly the same. You conclude it didn’t work. You pack it up as a failure, never realizing your device worked. 
What if it is a duplicate universe but some time back? He would have thought he was time travelling.
Did your alternate self do the exact same thing at the exact same time but over to your original universe? I’m sure “universe shifters” have a term for this problem.
I expect them both to leave at the same time.
I dun’ geddit. But anyway.
-FrL-
There are levels of infinities. The infinity of irrational numbers is larger than the infinity of counting numbers. By raising infinity to the power of infinity over and over, one can create an infinite number of infinities, all of different sizes. Another reason why one can have an infinite number of possible universes without necessarily having duplications.
Which post is this in response to?
-FrL-
That’s why I don’t believe in them - especially not parallel from the beginning. Most sf parallel universes are of the second type, which I don’t think has this problem. Not that I believe in them either.