The universe can be a very strange place. While groundbreaking ideas such as quantum theory, relativity and even the Earth going around the Sun might be commonly accepted now, science still continues to show that the universe contains things you might find it difficult to believe, and even more difficult to get your head around.
Theoretically, the lowest temperature that can be achieved is absolute zero, exactly −273.15°C, where the motion of all particles stops completely. However, you can never actually cool something to this temperature because, in quantum mechanics, every particle has a minimum energy, called “zero-point energy,” which you cannot get below. Remarkably, this minimum energy doesn’t just apply to particles, but to any vacuum, whose energy is called “vacuum energy.” To show that this energy exists involves a rather simple experiment– take two metal plates in a vacuum, put them close together, and they will be attracted to each other. This is caused by the energy between the plates only being able to resonate at certain frequencies, while outside the plates the vacuum energy can resonate at prettymuch any frequency. Because the energy outside the plates is greater than the energy between the plates, the plates are pushed towards each other. As the plates get closer together, the force increases, and at around a 10 nm separation this effect (called the Casimir effect) creates one atmosphere of pressure between them. Because the plates reduce the vacuum energy between them to below the normal zero-point energy, the space is said to have negative energy, which has some unusual properties.
One prediction of Einstein’s theory of general relativity is that when a large object moves, it drags the space-time around it, causing nearby objects to be pulled along as well. It can occur when a large object is moving in a straight line or is rotating, and, although the effect is very small, it has been experimentally verified. The Gravity Probe B experiment, launched in 2004, was designed to measure the space-time distortion near Earth. Although sources of interference were larger than expected, the frame-dragging effect has been measured to an uncertainty of 15%, with further analysis hoping to reduce this further.
Relativity of Simultaneity
The relativity of simultaneity is the idea that whether two events occur simultaneously or not is relative and depends on the observer. It is a strange consequence of the special theory of relativity, and applies to any events that happen that are separated by some distance. For example, if a firework is let off on Mars and another on Venus, one observer traveling through space one way might say they happen at the same time (compensating for the time light takes to reach them), while another observer traveling another way might say the one on Mars went off first, and yet another might say the one on Venus went off first. It is caused by the way different viewpoints become distorted compared to each other in special relativity. And because they are all relative, no observer can be said to have the correct viewpoint.
This can lead to very unusual scenarios, such as an observer witnessing effect before cause (for example, seeing a bomb go off, then later seeing someone light the fuse). However, once the observer sees the effect, they cannot interact with the cause without traveling faster than the speed of light, which was one of the first reasons faster-than-light travel was believed to be forbidden, because it is akin to time travel, and a universe where you can interact with the cause after the effect makes no sense.
Shorty after the Big Bang, the universe was in a highly disordered and chaotic state. This means that small changes and defects didn’t change the overall structure of the universe. However, as the universe expanded, cooled, and went from a disorderly state to an orderly one, it reached a point where very small fluctuations created very large changes.
This is similar to arranging tiles evenly on a floor. When one tile is placed unevenly, this means that the subsequent tiles placed will follow its pattern. Therefore, you have a whole line of tiles out of place. This is similar to the objects called cosmic strings, which are extremely thin and extremely long defects in the shape of space-time. These cosmic strings are predicted by most models of the universe, such as the string theory wherein two kinds of “strings” are unrelated. If they exist, each string would be as thin as a proton, but incredibly dense. Thus, a cosmic string a mile long can weigh as much as the Earth. However, it would not actually have any gravity and the only effect it will have on matter surrounding it would be the way it changes the form and shape of space-time. Therefore, a cosmic string is, in essence, just a “wrinkle” in the shape of space-time.
Cosmic strings are thought to be incredibly long, up to the order of the sizes of thousands of galaxies. In fact, recent observations and simulations have suggested that a network of cosmic strings stretches across the entire universe. This was once thought to be what caused galaxies to form in supercluster complexes, although this idea has since been abandoned. Supercluster complexes consist of connected “filaments” of galaxies up to a billion light-years in length. Because of the unique effects of cosmic strings on space-time as you bring two strings close together, it has been shown that they could possibly be used for time travel, like with most of the things on this list. Cosmic strings would also create incredible gravitational waves, stronger than any other known source. These waves are what those current and planned gravitational wave detectors are designed to look for.
Antimatter is the opposite of matter. It has the same mass but with an opposing electrical charge. One theory about why antimatter exists was developed by John Wheeler and Nobel laureate Richard Feynman based on the idea that physical systems should be time-reversible. For example, the orbits of our solar system, if played backwards, should still obey all the same rules as when they are played forwards. This led to the idea that antimatter is just ordinary matter going backwards in time, which would explain why antiparticles have an opposite charge, since if an electron is repelled while going forwards in time, then backwards in time this becomes attraction. This also explains why matter and antimatter annihilate. This isn’t a circumstance of two particles crashing into and destroying each other; it is the same particle suddenly stopping and going back in time. In a vacuum, where a pair of virtual particles are produced and then annihilated, this is actually just one particle going in an endless loop, forwards in time, then backwards, then forwards, and so on.
While the accuracy of this theory is still up for debate, treating antimatter as matter going backwards in time mathematically comes up with identical solutions to other, more conventional theories. When it was first theorized, John Wheeler said that perhaps it answered the question of why all electrons in the universe have identical properties, a question so obvious that it is generally ignored. He suggested that it was just one electron, constantly darting all over the universe, from the Big Bang to the end of time and back again, continuing an uncountable number of times. Even though this idea involves backwards time travel, it can’t be used to send any information back in time, since the mathematics of the model simply doesn’t allow it. You cannot move a piece of antimatter to affect the past, since in moving it you only affect the past of the antimatter itself, that is, your future.
It is not strictly science, but rather a very interesting set of mathematical theorems about logic and the philosophy that is definitely relevant to science as a whole. Proven in 1931 by Kurt Gödel, these theories say that with any given set of logical rules, except for the most simple, there will always be statements that are undecidable, meaning that they cannot be proven or disproven due to the inevitable self-referential nature of any logical systems that is even remotely complicated. This is thought to indicate that there is no grand mathematical system capable of proving or disproving all statements. An undecidable statement can be thought of as a mathematical form of a statement like “I always lie.” Because the statement makes reference to the language being used to describe it, it cannot be known whether the statement is true or not. However, an undecidable statement does not need to be explicitly self-referential to be undecidable. The main conclusion of Gödel’s incompleteness theorems is that all logical systems will have statements that cannot be proven or disproven; therefore, all logical systems must be “incomplete.”
The philosophical implications of these theorems are widespread. The set suggests that in physics, a “theory of everything” may be impossible, as no set of rules can explain every possible event or outcome. It also indicates that logically, “proof” is a weaker concept than “true”; such a concept is unsettling for scientists because it means there will always be things that, despite being true, cannot be proven to be true. Since this set of theorems also applies to computers, it also means that our own minds are incomplete and that there are some ideas we can never know, including whether our own minds are consistent (i.e. our reasoning contains no incorrect contradictions). This is because the second of Gödel’s incompleteness theorems states that no consistent system can prove its own consistency, meaning that no sane mind can prove its own sanity. Also, since that same law states that any system able to prove its consistency to itself must be inconsistent, any mind that believes it can prove its own sanity is, therefore, insane.