Question about a mirror Universe

Question

In the article We've seen signs of a mirror-image universe that is touching our own in the popular magazine “New Scientist” (which describes a real scientific theory though, though in a popular form, but I think that's not a problem in this case) one can read that Leah Broussard has dusted off an already old theory (by Lee and Yang), and tried to reanimate it: The Mirror Universe.

It says, for example:

The article you are reading is written back to front.

But how can this be? I can imagine that the clock goes backward (though not time itself). Just look in the mirror and you'll see it's true.

But when I look in the mirror I can't see that someone who's writing a piece of text starts at the end and working his/her way to the beginning. What I do see though is that the one who writes starts at the beginning but writes from the right to the left, like in Arabic (you can check this out again by looking to someone who's writing in a mirror). Now, according to me, someone can't write a book from the back to the cover. Causality is violated here. Can the dead come out their graves alive, growing "older" until they are being pushed back in the uterus, after which they get smaller and smaller until only semen and an egg is all that's left and one can say they are dead.

Now, do I interpret the quote wrong, or are texts really written backward from the end to the beginning?

In the answer by@PM 2Ring (below) one can read:

The t=0 instant of the Big Bang is at the left side of that diagram, and time progresses towards the right side. Make a mirror-image of that diagram, with its t=0 Big Bang point on its right side, so time in that diagram progresses towards the left.

How can the arrow of time have two different directions? I mean, of course, you can mirror an arrow. But time in both Universa proceeds in the same way as in ours (or relative to ours: if 100 000 years have passed in our Universe then also in the Mirror Universe this "amount" of time will also have passed. Also from our point of view time in the MU passes normally and only the direction of time's arrow is different.

Doesn't this mean that time isn't really going backward which is implied by my first quote (surely the clock ticks opposite to ours, just look in a mirror to see this) and the only differences between these two Universes are the fact that we see only particles while in the MU

I know this is not mainstream (at this time anyway), and maybe a link can be laid with the Rishon model which proposes a substructure of quarks and leptons and says that in our Universe there are equal amounts of matter and anti-matter, and maybe another Universe where all the particles are the anti-particles of ours (though the amount of Rishons and anti-Rishons is the same in both Universes, they are differently combined in each), but I'm really fascinated by this theory and that's why I nonetheless ask this question.

Answer 1

I haven't looked at the New Scientist article (it's behind a paywall), but in the original Mirror Universe model, the arrow of time in our universe points in the exact opposite direction to the arrow of time in the mirror image universe.

So relative to us, their time is running backwards. But that's not an issue, since the only point the two universes have in common is the exact instant of the Big Bang, so no causality paradoxes can arise.

To illustrate this, let's start with this Big Bang diagram from the top of Wikipedia's Big Bang article.

The $t=0$ instant of the Big Bang is at the left side of that diagram, and time progresses towards the right side.

Make a mirror-image of that diagram, with its $t=0$ Big Bang point on its right side, so time in that diagram progresses towards the left.

Join those 2 diagrams at their bases, the $t=0$ instant of the Big Bang. Now you have a diagram of the mirror universes, according to the original theory.

Leah Broussard is claiming that maybe that picture is misleading, and the topology is curved in a way that allows the space of our universe to be in some kind of contact with the mirror universe.

Answer 2

So to paraphrase the forgoing (please forgive the repetition of all that you have laid out - but I am trying to paraphrase what you AGREE): our universe has an antimatter partner on the other side of the Big Bang. This antimatter universe would be dominated by antimatter and have inverted spatial properties compared to our universe. The Big Bang should have created equal amounts of matter and antimatter, but there is almost no antimatter in the universe today. This is one of the biggest mysteries in physics. So perhaps according to Occam’s razor, a mirror image universe is the simplest answer! For this antimatter partner perspective to happen you have to devise a new cosmological model positing the existence of an “antiuniverse” which, paired with our own, preserves a fundamental rule of physics called CPT symmetry. C stands for the “charge” of particles. P stands for Parity meaning the orientation (sort of like looking into a mirror that also turned you upside down). T stands for Time which is seemingly reversed RELATIVE TO US in a mirror universe. Ouch! Time is reversed. However time in both Universes proceeds in the same way, and if 100,000 years have passed in our Universe, then this amount of time will also have passed in the mirror universe. In both universes, entropy would be expected to increase as time passes. So relative to us, their time is running backwards. However, that is not an issue since the only point the two universes have in common is the exact instant of the Big Bang so no causality paradoxes can arise. As far as the people in the mirror universe are concerned, time is running forward, and their universe's entropy increases over time. But the stuff that they call matter, we would call antimatter if we could observe it, but we can never do that. So for them, time does not “go backward”. But relative to us it seemingly would if we could observe it but we cannot. So after the common Big Bang, the arrow of time in the mirror Universe points in the opposite direction to the direction of time in ours. But for them, it still points towards the future. When you mirror the universes they only intersect at the Big Bang. Then both Universes develop in opposite directions. This does not mean they are closer to entropy right now while we are closer to the “beginning”. What it means is that they do not share this “moment”. They exist elsewhere with a “moment” of their own. They do not exist on our timeline and we do not exist on theirs is what it means. We only “existed” for each other at the moment of the Big Bang. All this thinking is exhausting. But is that a reasonable statement of the collective view expressed above?

Answer 3

So how does the other universe go “backward” in time RELATIVE TO US? Well, think about it. It is kind of misleading as a statement. You are at a point 76.6 sextillion miles from the beginning and 13,035,000,000 years (i.e. 13.035 light years) from the Big Bang. To reach a person at the same point in the mirror universe, which is on an entirely different arrow of time, you would have to go back 13,035,000,000 years, and then go forward in the alternate universe another 13,035,000,000 years. So you would have to travel back through the Big Bang and make a journey in time of 26,070,000,000 years. Or would you? Would travelling back through time and travelling forward through anti-time cancel each other out? One thing is for sure; if you reached another you composed of anti-matter in the alternate universe and shook hands with that person you would both disappear and in a puff of smoke. Well not in a puff of smoke, in a cataclysmic explosion because you would release one helluva lot of energy.