Mirror Matter

Imagine a universe like ours only all particles are replaced with antiparticles, left and right are reversed, and the direction of motion for all particles is reversed. Don't think too hard; such a universe would be indistinguishable from ours by the laws of physics. The same would be true if we left out the last condition. That is, life would be exactly the same for people who were our mirror images and were made out of antimatter.

If the laws of physics are unchanged under all three laws, and under only the first two, it must also be true that they are unchanged under the third condition only (Perform all three operations, then perform the first two). This means that a universe in which all is the same except for the direction of motion (i.e. the direction of time) is identical to ours. Einstein's special relativity implies such observers, which can best be shown through representation in Minkowski spacetime. Minkowski spacetime is a four dimensional manifold in dimensions, x,y,z, and ct where c is the speed of light. In the image below, as is commonly done, the dimension z is omitted so we can visualize the manifold. The speed of light determines the boundaries.
For an event at (0,0,0), any observer in our universe is represented by a point in the upper cone. For all observers whose spacetime coordinates fall in the lower cone, time is reversed.

Such transformations demonstrate the symmetry of our universe. For anything to be symmetrical, you must be able to exchange the (two) parts without changing anything. Upon the observation that subatomic particles called neutrinos only spin left, a theory of mirror matter was formed, by which every particle has a mirror "twin" that spins in the opposite direction, restoring the symmetry. Such particles would be invisible to us, as our photons (light particles) all spin in one direction, allowing us to see only half of the predicted particles.

Although these particles would be invisible to us and have little to no effect on our universe, they would be affected by gravity (the weakest force, but the only force that is not exchanged through particles, by modern physics). But if that's the case, how could we still not know whether mirror matter actually exists? Many people believe that "dark matter," hypothetical matter that is undetectable by its emitted radiation but effects visible matter via gravity, is in fact mirror matter. Dark matter is postulated to explain missing mass in our galaxies, and may account for more than half of the matter in our universe. Observations of the rotational speeds and temperature distribution of galaxies strongly suggest dark matter's existence.

Just to be clear, there is no "mirror universe," mirror matter would exist in our space-time. In fact, Robert Foot also suggests in his book "Shadowlands: Quest for Mirror Matter in the Universe" that meteorites of mirror matter may collide with our Earth, causing catastrophic events, that seem unexplained. He gives an explosion in Siberia in 1908 as an example, among 6 others. Also, he claims that it is likely that many planets which we perceive as starless, are in fact rotating stars composed of mirror matter.

Perhaps the most interesting thing about mirror matter is that if mirror matter does exist, it is likely that time is reversed for such matter. Meaning left and right would be reversed, and so would time. And although there is no mirror universe, mirror matter should have the same physics as observed matter. This is a result of the fact that our laws are unchanged by the direction of time as long as everything in the system stays consistent. And in fact, reversing time does change the spin from left to right. If a neutrino were coming towards you, it would be spinning left (clockwise), meaning if it were moving away from you, as if the event had been rewound like a VHS, it would appear to be spinning counterclockwise.

Presuming symmetry has led to several discoveries in physics. Consequently several types of matter have been proposed to preserve symmetry:

1. Antimatter

• A new form of matter necessary to make Einstein's theory of relativity consistent with the quantum mechanical theory of the electron.
• Predicted by Dirac who noticed that the mathematical description of the electron would only exhibit Lorentz symmetry (the four dimensional rotational symmetry of space-time) if such matter existed.
• Particles have the same masses as their corresponding anti-particles.
  
• Has been experimentally verified.
  

2. Supersymmetric partner particles

• Necessary for String theory to accurately describe our universe.
  
• Particles have the same mass as their superpartners, although broken symmetry causes the mass of superpartners to be so high that these particles could only be seen at very high energies.
• Particles also have the same charge as their superpartners.
• One superpartner is a fermion (a particle with half integer spin, which as far as we know is always a matter particle) and the other is a boson (a particle with integer spin, typically a force carrying particle).
• Has not been experimentally verified but may be in the next decade using the Large Hadron Collider.
  

3. Mirror Matter

• Developed to preserve symmetry despite the fact that most fundamental particles are left-handed.
• Mirror particles interact with ordinary particles via gravity only.
• Has not been experimentally verified but poses as an interesting solution to what dark matter is.
  

My question: Is the theory of mirror matter inconsistent with String theory by which the force of gravity is in fact carried by a particle, the graviton? Can both theories be correct? If not, what is more likely: that gravity is in fact the only force not carried by a particle, or that our universe despite possessing many symmetries is overwhelmingly unbalanced in favor of left-handed particles?

Foot says "The prospect that the most natural symmetry imaginable -- mirror symmetry-- is not a symmetry of nature, while every other obvious symmetry such as rotational symmetry and translational symmetry are indeed symmetries seems rather surprising to say the least." Then again it also seems surprising that all of the fundamental forces besides gravity can be unified.

Foot can't seem to promote his own theory without undermining supersymmetry and String theory. But I like both.

Hyperspace

It is particularly challenging but interesting to consider other dimensions of space and time. Physicists became interested in the idea of additional dimensions upon developing string theory, which despite being somewhat controversial, as there are few conceivable ways to test such a theory, is currently our best prospect for a complete physical theory --it would make sense on both small scales and large scales, would unify the fundamental forces, and would actually predict gravity instead of just observing it-- and happens to make the most sense in 10 or 11 dimensions. Regardless of whether string theory proves to be accurate, many physicists see no reason as to why our universe should not have more dimensions than we can perceive. A line exists in one dimensional space, but it also exists in 2-D space, 3-D space, 4-D space, and so on.

Studying extra dimensions has spawned additional theories of wormholes, parallel universes, and the multiverse. Higher dimensions make up what is typically called hyperspace.

Almost any physicist or mathematician working in this field will reference "Flatland," a book written in 1884 by Edwin A. Abbot, when trying to explain their work to the public. I still haven't read Flatland but I've become very familiar with the story. It takes place in a two dimensional world called Flatland and is narrated by a character named "A. Square" who presents to the reader life in a two dimensional world. The story is designed to provoke thought concerning dimensions other than the ones with which we are familiar, and A. Square himself is forced to do the same. First when he visits a one dimensional world in a dream, and then when he is visited by a three dimensional sphere who appears to him as a circle increasing and then decreasing in size.

Flatland is so frequently referenced because the idea extends easily to our own perception. It raises questions of what a 4-dimensional object would look like, and to the true nature of reality. Similar to A. Square's perception of a sphere, a four dimensional object would appear to us in 3-dimensional cross sections. A 4-D sphere, or hypersphere would appear to be a sequence of spheres increasing in size and then decreasing, finally vanishing into a point. We would only be able to see the object in its entirety throughout time (another dimension) but could never imagine its spatial form.

Recently, in trying to understand multiple dimensions and my own perception, I've been trying to deconstruct my experience as an observer. In a single moment, time has no dimension; it is only a point. Space should have three dimensions but without time, I can only perceive two dimensions. Therefore it is my memory and my mind which allow me to assemble these splices to create three spatial dimensions and one time dimension; a succession of moments in space.

I still can't wrap my head around the fact that physical positions are so transient and what it could mean in terms of dimensions. If I move my hand, there is nothing in the space that it occupied. It reminds me again of perceiving only splices of a continuous physical thing. In a video called imagining the tenth dimension which contributed to my early interest in higher dimensions, to help imagine another dimension, the viewer is asked to consider a long "snake" that would correspond to his or her entire life's path. Our experience then consists of cross sections of this 4-dimensional "snake" and if we know we are viewing cross sections, why can we not infer another dimension? If all of our experiences were to persist in physical space, space would become overcrowded. It would require at least another dimension to compensate. If I know that 10 minutes ago I was sitting on my couch and now I am sitting on my bed, I am confident that both are part of reality but the self that was on the couch 10 minutes ago has vanished and will never be again. In every moment time and space are changing and all of experience is piecing together traces. If these moments are not in fact connected, we would not be able to experience them sequentially as we do. Time would never pass. I have read in several books on some of the subjects I have been discussing that we could stack two dimensional surfaces on top of one another to obtain a 3-dimensional object, but that is not true! If the surfaces are in fact two dimensional, they have no thickness and we can stack as many on top of one another as we'd like, we will still have a two dimensional surface. Many theories permit the existence of multiple dimensions by deducing that they must be so small that they are invisible to us. I feel like there must be some "thickness" to our moments; another very small dimension; something that allows time to pass. It has confused me for a while that even though there are an infinite number of numbers between 0 and 1, we can in fact go from 0 to 1. For me it is proof that space and time are not in fact continuous but discrete, but it's something I'm still thinking about.

As I said earlier, these are just ideas. Often when I write things of this nature it is out of confusion. It's possible that in a couple days I will understand why this can't be so. Or come to another understanding of what may be going on. In the meantime it's interesting to think about. I was originally attracted to science and math because of the certainty involved, particularly in math. If you accept very basic and obvious statements to be true you can use these statements to build more complicated ones that eventually build off of each other to create advanced and beautiful theorems whose validity becomes unquestionable. It has always seemed a waste of time to me to learn things that may not be true. Yet I find myself infatuated with theoretical physics, a science which was once undoubtedly a science, but now will more closely resemble philosophy or science fiction at times. Theories by some of the most respected physicists can seem too far out to believe, and it can be hard to know what to take seriously. The idea that so much is unknown leaves a lot of possibility and people are starting to get creative.