According to string theory, the universe has not just three or four dimensions, but eleven dimensions, ten of space and one of time. We do not observe the extra spatial dimensions because they are curled tightly around each other.

The Roman poet Lucretius (ca. 94–ca. 55 B.C.) wrote a poem in 56 B.C. describing the views of Greek philosophers who, like him, believed the universe to be composed of atoms. This poem is the only record of the beliefs of these early atomists, whose works were lost due to their unpopular views. Lucretius' poem was lost as well, but a copy was discovered in 1417. Its views helped to persuade chemists to consider the atomic theory of matter, a theory that won out eventually.

The Ancient Greek philosopher Thales noticed that amber decorations on spinning wheels attracted threads, feathers, and other objects through what we now know to be static electricity. The Greek word for amber is elektron, from which William Gilbert, physician to Queen Elizabeth I, coined the word "electricity".

In 1903, Albert Michelson, one of the 19^th century's top physicists, commented "The more important fundamental laws and facts of physical science have all been discovered, and these are so firmly established that the possibility of their ever being supplemented in consequence of new discoveries is exceedingly remote". Two years later, Einstein published his revolutionary Theory of Special Relativity.

Einstein's ideas on relative acceleration were partly inspired by the free fall of a man who fell off a roof in Berlin. The man, who survived without injury, told Einstein that he had not felt the effects of gravity.

In 1905 Albert Einstein wrote his famous Special Theory of Relativity. It was published in a scientific journal that same year, but took many years to gain general acceptance. In fact, it was not verified by actual experiment until 25 years later. Two years after that paper was published, Einstein wanted a job as assistant professor of mathematics. This job required the applicant to submit a thesis paper, so Einstein submitted his Special Theory of Relativity. The university rejected it.

The quark, a building block of the proton, got its name from James Joyce's Finnegans Wake, from the line "Three quarks for Muster Mark! Sure he hasn't got much of a bark". (source)

According to the laws of gravity, the moon technically does not orbit the Earth. The two bodies actually both orbit around their common centre of gravity, which is located 1,000 miles beneath the surface of the Earth and is on a straight line between the centres of the Earth and moon. The centre of the Earth makes a small circle around that centre of gravity every 27⅓ days.

According to the rules of logic, the question "What would happen if an irresistible force met an immovable object?" is meaningless. In a universe where one of the above exists, the other cannot by definition. (source)

A "light year" is a measure of distance, not time. It is defined as the distance light travels in one year. Light moves at a velocity of about 300,000 kilometres each second, so in one year, it travels about 9,500,000,000,000 kilometres. (source)

To the nearest ten-thousandth of a mile, light travels at 186,282.3959 miles per second. At that rate, it takes slightly more than eight minutes to get to Earth from the sun. However, it takes light hundreds of years to travel from the sun's centre to its surface. The light must take a very indirect path to the surface due to the large number of collisions with particles within the sun.

In 1940, the Tacoma Narrows Bridge (popularly known as "Galloping Gertie"), which spanned the Puget Sound south of Seattle, opened. At the time it was the third longest bridge in the world and narrower than any comparably-sized bridges. Although the bridge was criticized for being too slender, Leon Moisseiff, the consulting engineer to the project and an expert on suspension bridges, assured people that the bridge would be safe. However, only three months after it opened, the bridge collapsed in a 42 miles per hour wind after going into harmonic oscillation. (source)

An atomic clock kept at the National Bureau of Standards in Boulder, Colorado, U.S.A., 1,650 metres above sea level, gains about five microseconds each year relative to an identical clock kept at the Royal Greenwich Observatory, 25 metres above sea level. The reason is that gravity gets stronger as one gets closer to the Earth's core, and, according to Einstein's Theory of Relativity, time is slower in stronger gravitational fields.

A perpetual motion machine would violate the laws of thermodynamics. No-one has ever built one, and no-one ever will. (source)

According to the Second Law of Thermodynamics, the amount of entropy in the universe always increases, which means that eventually, the universe must run down and life in the universe will cease. (source)

Information about what has fallen into a black hole is stored on the black hole's event horizon. Recent calculations by those who study quantum gravity theory and superstrings have confirmed what Stephen Hawking and his collaborators proposed a decade or more ago. Evidently, the information contained in matter that falls into a black hole is by some curious means encoded in the pattern of frozen quantum fields at the horizon. This raises some interesting possibilities that we could resurrect clocks, humans, spacecraft, and whole planets into something like their pristine form if we could magically reverse the in-fall and collapse process. Many believe that this mathematical result means that we have reached a watershed moment in history in understanding the connection between quantum mechanics and gravitation theory. Quantum mechanics deals with statements about the information that we can extract about a quantum mechanical process involving observation. Now this same information can be applied to configurations of the gravitational field and space-time itself. (source)

While light has no mass, it has weight. Weight is a measurement of the pull of gravity on something, and light can be bent by gravity. (source)

Why is the sky blue? The sky is blue because of refraction. The sun's light is of all colours of the rainbow, mixed together to make white light. The reds and yellows pass through air easily, but some of the blue portion of sunlight is scattered in every direction by air molecules. This scattering causes the sky to be blue.

An article in the April 26, 1993 article of Physical Review Letters, titled "First Measurement of the Left-Right Cross-Section Asymmetry in the Boson Production by e⁺ e^- Collisions", had 407 authors. (source)

It is not possible to hear in space. Because there is no atmosphere in space to conduct the sound, it would not carry. So, the object would make a noise, but it would not carry to any receiver, and no one would hear it. (source)

There is sound in space. Sound is a pressure wave, and as long as there is some kind of gaseous medium, there is the possibility of forming pressure waves in it. In space, the interplanetary medium is a very dilute gas at a density of about 10 atoms per cubic centimeter, and the speed of sound in this medium is about 300 kilometers per second. Typical disturbances due to solar storms and "magneto-sonic turbulence" at the Earth's magnetopause have scales of hundreds of kilometers, so the acoustic wavelengths are enormous. Human ears would never hear them, but we can technologically detect these pressure changes and play them back for our ears to hear by electronically compressing them. (source)

Since the 1950s, physicists have discovered over 200 different kinds of particles. (source)

The difference between the appearance of a real object and its reflection in a mirror is that the clockwise and counterclockwise directions are switched.

Newton's Third Law of Motion states that for every action there is an equal and opposite reaction. (source)

When an airplane travels at a speed faster than sound, density waves of sound emitted by the plane accumulate in a cone behind the plane. When this shock wave passes, a listener hears a sonic boom. (source)

It is not known exactly what gravity is. We can define what it is as a field of influence, and with general relativity we can think of it as being a property of our real world mathematically equivalent to not just the geometry of space-time, but equivalent to space-time itself. Some believe that the gravitational force is transmitted by particles called gravitons that travel at the speed of light just as photons do. In any true fundamental sense, we do not know what gravity is, we only know how it operates in various corners of our universe. Without gravity, there would be no space and time. (source)

Around one percent of the static on a television set tuned between stations is a relic of the Big Bang. (source)

Ordinary matter consists almost entirely (99.9999999999999%) of empty space. (source)

Bell's Theorem states that certain measurements made on one particle can instantaneously affect the measurements made on a second particle that, in theory, could have been removed to the opposite side of the galaxy, with no physical connection between the two. (source)

The size of Earth is roughly the geometric mean of the size of the universe and the size of an atom, and the mass of a human is roughly the geometric mean of the mass of Earth and the mass of the proton. (source)