Tesseracts and Time Travel

Over the last few weeks we've been looking at entries based upon a list of questions given to me by high school senior Jim Evins for a paper he was writing about my project. We'll conclude with three more questions.

"In chapter 3 of your book you discuss the possibility of an alien race that moves backwards in time. If they were to show up in the year 3000 and attain victory over earth, and we attain victory in our flow of time, would we not just destroy one another’s history and reverse the reality of who showed up first on our planet?"

The accepted definition for anti-matter is that it’s matter which is moving backwards in time. That underlying “sea of information” that we looked at in the first question is ultimately symmetrical, a balanced whole, where every positive and negative can exist simultaneously, and our universe or any other is defined in part by how it breaks that symmetry: this is why our universe is made primarily of matter rather than anti-matter. Physicist Sean Carroll talks about how the existence of our universe means there should be a corresponding universe made up primarily of anti-matter, and in that universe time’s “arrow” would be in the opposite direction to ours.

But if matter and anti-matter interact, they destroy each other. So the reverse time aliens I’m describing in the thought experiment you’re referring to are made of the same matter as us, but they perceive time to flow in the opposite direction. How could that be possible? In my book I describe how for us, time appears to flow in one direction only because we derive our energy from chemical processes which obey the thermodynamic laws of entropy, and many physicists talk about the fact that our universe started with extremely low entropy and will end with extremely high entropy. But physicists also talk about “time reversal symmetry” which means any process viewed in one direction of time should make just as much sense when viewed in the opposite direction. So with the scenario I was describing, these aliens derive their energy from some other process which moves in time’s opposite direction, and hence they perceive time to move in the opposite direction to ours. I propose that it would be possible for both races to destroy each other, and yet both could survive within their own perceived version of reality. How? Because quantum mechanics tells us there are many possible pasts and many possible futures. So just as Everett’s Many Worlds Interpretation tells us the universe must exist where I lost my leg as a child, that universe has nothing to do with the one I’m observing, it has no effect on my reality.

Again, if you believe there is only one possible past, present and future for our universe then conversations such as these would be fraught with paradox. But this deeper understanding of how we move within a constantly evolving probability space, and how the probability space I had one minute, one year, or one decade ago is not the same probability space as I’m within right “now” allows us to see how this thought experiment would work: the aliens could destroy us, we could destroy the aliens, but those two universes do not directly affect each other because they are part of our universe’s 6D phase space.

"Are you aware of 4 dimensional objects such as tesseracts, pentatopes, and rotatopes, and if so how are they incorporated (if at all) into your view of the fourth dimension?"

I talk about extra-dimensional shapes such as these regularly in my blog or on my youtube channel . Here’s a link to the blog entry and video for Imagining the Fourth Dimension, my blog entry which most recently deals with this question: http://imaginingthetenthdimension.blogspot.com/2011/08/imagining-fourth-dimension.html

In a nutshell: there’s a difference between a concept such as cube, and a physical cube. Likewise, there’s a difference between tesseract as a concept, and a physical object that is in the shape of a tesseract. What do I mean by this? A 3D cube as a concept can be freely discussed as an idea, but if a cube had length, width and depth within 3D space but no duration within 4D space-time it would be impossible for us to view such an object. Likewise, a 4D hypercube or tesseract can be discussed as a concept, but it would be impossible for us to view such an object unless it had a duration within the fourth dimension. When we look at animations of rotating tesseracts, then, we are looking at a visualization of how cross-sections of that object would appear within the third dimension, one frame after another, and we’re not really viewing the tesseract in its entirety.

"Do you feel it’s possible to reverse our sense of time and flow the opposite way, or do we have to maintain the flow we were born into?"

With our physical bodies, we are stuck with our “arrow of time” because of those thermodynamic processes I spoke of above. The only way that we can currently perceive these extra dimensions, or time flowing in the opposite direction, is with our minds and the power of imagination.

Thanks again, Jim, for your insightful questions. Next week, we'll look at Poll 92 - Is there only one inevitable timeline for our universe?

Enjoy the journey!

Rob