The 10 Most Mind-Boggling Unexplained Mysteries In Physics


How did the universe begin?


This seems as good a place as any to start. One of the big unanswered questions in physics is just how the universe originated. The most common explanation, of course, is the Big Bang theory, but that itself is not without its problems. For starters, what happened just before the Big Bang is beyond our visible reach. In addition, the Big Bang should have resulted in the formation of both matter and antimatter in equal amounts. And, as their names may suggest, any time these two collided they would annihilate each other, releasing energy in the process. Regardless of how common such collisions might be, though, the expected result would be to see equal amounts of both still today. But, strangely, we see in our observable universe mostly matter.


So where did all the antimatter go? Or, put another way, how did we end up with so much matter? To get around this conundrum, theoretical physicists from the United States and the United Kingdom proposed, in 2001, the “ekpyrotic scenario.” The idea is that the universe runs in cycles and that massive sheet-like parts of our universe – or “branes” – collide with each other once every trillion years, leading to enormous Big Bang-style explosions. And instead of introducing an even division of material, these explosions then re-inject both matter and energy into the equation.

Dark matter and dark energy



But if pondering the lack of antimatter in the universe already has your head spinning, then get this: there are also two so-called dark “substances” in our universe – namely, dark matter and dark energy. And together they task physicists with some of the most baffling questions. Essentially neither of these can be seen or touched, and yet they’re both incredibly important to our understanding of the universe.


Scientists rely on dark energy to explain why some galaxies are being constantly pushed away instead of gravitating toward one another. Indeed, to make the calculations work, physicists need an abundant amount of the stuff; theoretically, dark energy makes up 70 percent of the universe. Dark matter, meanwhile, is even stranger, because while this stuff has gravitational pull – like normal matter, thus giving scientists a way to detect it – what it actually consists of is a huge mystery.

The Boltzmann brain paradox



This one’s even more difficult to get your head around. Named after physicist Ludwig Boltzmann, a key player in building the theory of thermodynamics, a Boltzmann brain is a theorized self-aware brain, with memories and thoughts equal to our own, that would randomly pop into solitary existence floating around in a chaotic universe.


Essentially, it’s a thought experiment that cosmologists can play when considering the laws of thermodynamics. With time, it’s theorized, comes more disorder – in a closed system, anyway. Make that system an open one, though, and added energy can then bring back order. So, if our universe is indeed a closed system, then the paradox goes that human life and the observable orderly universe we live in are all part of an incredibly rare fluctuation in an otherwise orderly system.

Indeed, according to Boltzmann, such a fluctuation would be so rare that it’s much more likely to be outnumbered considerably by smaller fluctuations that would produce self-aware “brains” seemingly out of nowhere. Further, if that rare fluctuation occurred to produce humans and human consciousness, then the universe should have innumerable “brains” floating throughout it, too. And since these brains are self-aware and possess memories just like we do, who’s to say we aren’t all Boltzmann brains and that we only see the world as orderly because that’s how we make sense of it?

Why can’t we imagine four dimensions?



One of the other difficult aspects of living in a three-dimensional world is thinking beyond those dimensions. Okay, so it’s not so hard to add time as a fourth dimension, but we’re talking just spatial coordinates here. And for advanced mathematical theories, such as string theory, as many as 11 different dimensions are key, which boggles the mind. Time to pull out your holographic chess board.


Yet the fourth dimension of space is a mathematical reality. The tesseract, for example, is a 4D cube. Now, if you can, imagine turning a 2D square into a 3D cube and then taking that 3D cube one dimension further so that instead of six square faces it now has eight cubical cells on every surface. Hard to fathom? Don’t worry. Imagine how tough it would be for a creature from a 2D world to truly comprehend ours.

Are there parallel universes?



This is a mystery that’s backed up by logic, but it’s the sort of logic that’s almost impossible to physically prove. Still, there are several theoretical ways to create parallel universes, or even multiverses. You can start out, for example, by playing with the concept of space-time. Our universe is likely flat, according to the amount of cosmic microwave background radiation that we can detect and the distribution of galaxies we can see. Nevertheless, we could be limited by our view and by not seeing the curved edges of space just beyond our horizon. And if space-time is also flat, and therefore infinite, then perhaps ours isn’t the only universe sewn into the fabric of space-time. Oh, and even more bizarrely, the concept of a quilted multiverse allows for repetitions of the same universe.


The reason for the repetitions comes from having only a finite number of ways for particles to arrange themselves in a universe or even in a multiverse. So a multiverse that is infinite is bound to have patches that repeat themselves – patches that are only different in the positioning of one single particle and also patches that are radically different. But none of the patchwork patterns in the quilted multiverse can see beyond their own visible horizon. So if a copy of you is running around in a universe doing the same thing, or maybe making just slightly different decisions, there’s no way to know for sure.

The observer effect



While the previous entries on this list have focused on some very big questions, this one looks at a much smaller but no less important mystery. The “observer effect” is an event in quantum physics whereby particles are in a state of multiple possibilities until they finally commit to one outcome – and this is the only state that anyone ever actually sees.


While it’s best described in the famous Schrödinger’s Cat thought experiment, the behavior is best demonstrated with the double-slit experiment. Originally designed to test whether light behaved as a particle or a wave, the double slit experiment showed that light in fact did both. Similar tests have since been carried out not only with light, such as laser beams, but also electrons and even helium atoms.

Basically, when the single particle is sent through a double slit to a sensor, an interference pattern characteristic to a wave is seen. But try to measure the path of the particle to see if it indeed behaved as a wave going through both splits at once, and the interference pattern disappears; all that is measured is the path through one or the other splitter without any interference pattern detected. And, curiously, while classic mechanics cannot explain the probability of how any one particular particle can behave this way, quantum mechanics does.

Can physics explain consciousness?



Here’s a strange thing: we’re thinking, feeling beings, but our brains are essentially made up of the same stuff as the rest of us. So what is it that gives us consciousness? What is it that makes us us? Well, some physicists have tried to explain that question using the quantum world.


Other natural phenomena like photosynthesis and electron transfer in proteins have been explained in this way, but as of yet no solid theory as to why we think has been put forward. Sir Roger Penrose and Stuart Hammerof have proposed that superposition, or the adding together of quantum states, could be responsible; however, other physicists, including Edward Witten, think that explaining consciousness is fundamentally impossible.

Quantum mechanics and the theory of everything



One of the strangest and most important branches of physics, quantum mechanics is a way of describing the interactions between incredibly small particles. And to say it’s weird would be an understatement. As Niels Bohr once said, “Everything we call real is made of things that cannot be regarded as real.”


But there’s a problem – of sorts. While both quantum mechanics and general relativity – our understanding of the larger forces in the universe – have both been rigorously tested and proven, there’s no so-called theory of everything that ties these two seemingly disparate concepts together. Essentially, we know why both things work, but we have no idea how or why they work together. Stephen Hawking has even gone so far as to suggest that such a theory is actually unobtainable.

The black hole information paradox



This mystery concerns what happens when objects enter black holes. A fundamental tenet of science is that information about a physical system should define that system at any point in time. But once something enters a black hole, that information is lost. Or is it? In fact, what we have is a conundrum on a dramatic scale.


We all know that nothing can escape a black hole, but if information is nevertheless lost then we’re violating a law of nature. And some of the theories that have been put forward to answer this paradox are even weirder than the question itself. One suggestion, for example, is that the information is deposited in a baby universe inaccessible to our own; another is that the information escapes once the black hole evaporates.

The end of the universe



Last, but not least, we come full circle back to the beginning of time as also being an indicator of how our universe may finish. What’s going to happen when, or if, the universe comes to an end? There are a number of different theories, none of which sound like they’re going to be very much fun. But then the end of things never is, is it?



The Big Rip theory, for example, suggests that eventually the universe will be moving apart at such a speed that its atoms will literally be torn apart. Another, the Big Crunch, is like the Big Bang but in reverse – with every bit of matter in the universe squishing together in a single, boiling mass of infinite density. Don’t worry, though: however we finish, it’s not likely to happen for another ten billion years.

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