A critical turning point (a watershed moment) in history is when something changes and things will never be the same again. This list looks through history at the most significant events that truly did change the world. Whether those changes are for the better or worse is obvious in most cases, but not always – especially as one can never compare the future if the watershed moment didn’t occur. Enjoy the list and add your own significant historical events to the comments.

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15. The Monorail

There is such a plethora of images of this type out there that I had to set a restriction; the restriction is that the images must include a planet – either a surface or from space. So, here they are – the top 15 stunning images from Science Fiction

14. Spike City

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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 ... Read more »

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 a ... Read more »

As is best shown in the equation E=MC², energy and matter are fundamentally connected. One effect of this is that energy, as well as mass, creates a gravitational field. A geon, first investigated by John Wheeler, in 1955, is an electromagnetic or gravitational wave whose energy creates a gravitational field, which in turn holds the wave itself together in a confined space. Wheeler speculated that there may be a link between microscopic geons and elementary particles, and that they might even be the same thing. A more extreme example is a "kugelblitz” (German for "ball lightning”), which is where such intense light is concentrated at a particular point that the gravity caused by the light energy ... Read more »

One of the longest outstanding mysteries in physics is how gravity is related to the other fundamental forces, such as electromagnetism. One theory, first proposed in 1919, showed that if an extra dimension is added to the universe, gravity still exists in the first four dimensions (three space dimensions and time), but the way this four dimensional space curves over the extra fifth dimension, naturally produces the other fundamental forces. However, we cannot see or detect this fifth dimension, so it was proposed that the extra dimension was curled up, and hence became invisible to us. This theory was what ultimately led to string theory, and is still included at the heart of most string theory analys ... Read more »

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 caus ... Read more »

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.

The expected effects were very c ... Read more »

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 reso ... Read more »