In the theory of relativity, time dilation is an actual difference of elapsed time between two events as measured by observers either moving relative to each other or differently situated from gravitational masses.

An accurate clock at rest with respect to one observer may be measured to tick at a different rate when compared to a second observer's own equally accurate clocks. This effect arises neither from technical aspects of the clocks nor from the fact that signals need time to propagate, but from the nature of space-time itself.

A case of time dilation in action is that astronauts actually return from their missions on the international space station (ISS) having aged less than the mission control crew that stayed on earth. Such time dilation has been repeatedly demonstrated (see experimental confirmation below), for instance by small disparities in atomic clocks on earth and in space, even though both clocks work perfectly (it is not a mechanical malfunction). The laws of nature are such that time itself (i.e. spacetime) will bend due to differences in either gravity or velocity - each of which affects time in different ways.

Stephen William Hawking, CH, CBE, FRS, FRSA (born 8 January 1942) is a British theoretical physicist, cosmologist, and author. His key scientific works to date have included providing, with Roger Penrose, theorems regarding gravitational singularities in the framework of general relativity, and the theoretical prediction that black holes should emit radiation, which is today known as Hawking radiation (or sometimes as Bekenstein–Hawking radiation).

He is an Honorary Fellow of the Royal Society of Arts, a lifetime member of the Pontifical Academy of Sciences, and in 2009 was awarded the Presidential Medal of Freedom, the highest civilian award in the United States. Hawking was the Lucasian Professor of Mathematics at the University of Cambridge between 1979 and 2009. Subsequently, he became research director at the university's Centre for Theoretical Cosmology.

Hawking has a motor neurone disease related to amyotrophic lateral sclerosis, a condition that has progressed over the years. He is now almost completely paralysed and communicates through a speech generating device. He has been married twice and has three children. Hawking has achieved success with works of popular science in which he discusses his own theories and cosmology in general; these include A Brief History of Time, which stayed on the British Sunday Times best-sellers list for a record-breaking 237 weeks.

Albert Einstein ( /ˈælbərt ˈaɪnstaɪn/; German: [ˈalbɐt ˈaɪnʃtaɪn] ( listen); 14 March 1879 – 18 April 1955) was a German theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics. While best known for his mass–energy equivalence formula E = mc² (which has been dubbed "the world's most famous equation"), he received the 1921 Nobel Prize in Physics "for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect". The latter was pivotal in establishing quantum theory within physics.

Near the beginning of his career, Einstein thought that Newtonian mechanics was no longer enough to reconcile the laws of classical mechanics with the laws of the electromagnetic field. This led to the development of his special theory of relativity. He realized, however, that the principle of relativity could also be extended to gravitational fields, and with his subsequent theory of gravitation in 1916, he published a paper on the general theory of relativity. He continued to deal with problems of statistical mechanics and quantum theory, which led to his explanations of particle theory and the motion of molecules. He also investigated the thermal properties of light which laid the foundation of the photon theory of light. In 1917, Einstein applied the general theory of relativity to model the structure of the universe as a whole.

Matan "Mat Zo" Zohar (born April, 1990) is a British trance music and progressive house music producer, composer and DJ.

The son of successful artist Israel Zohar, and half-brother of Israeli singer Alma Zohar, Matan Zohar was born in London, England in 1990. He was raised by his mother who was a professional violinist, who possessed staunch musical ethos and nurtured Matan's early love of--and prodigious inclination toward--music. From age one to eleven, Zohar and his family lived in the city of Cleveland, Ohio in the United States. It was there at age 8 where his father presented young Zohar with a guitar as a gift. He returned at age 11 to London and continued pursuing his musical interests as a drummer and bassist as a member of a jazz and rock band respectively. However, Zohar became more interested in musical acts such as Daft Punk and the Chemical Brothers, and his musical inclinations shifted to those of electronic dance music and DJing. After 3 years living and producing music in London, his recording began to gain attention and play time by other disc jockeys such as DJ Tarkan, Perry O'neil, Swedish Egil, DJ R-Man, Jav D, Micah, Airwave, Andy Moor and Markus Schulz In the 2009 publication of DJ Magazine's top 100 poll he was described by musical acts Above & Beyond, Lange and Daniel Kandi as a promising producer. In the 2010 publication, Mat Zo was a new entry at #66.

Neil deGrasse Tyson ( /ˈniːəl dəˈɡræs ˈtaɪsən/ born October 5, 1958) is an American astrophysicist and science communicator. He is currently the Frederick P. Rose Director of the Hayden Planetarium at the Rose Center for Earth and Space, and a research associate in the department of astrophysics at the American Museum of Natural History. Since 2006 he has hosted the educational science television show NOVA scienceNOW on PBS, and has been a frequent guest on The Daily Show, The Colbert Report, Real Time with Bill Maher, and Jeopardy!. It was announced on August 5, 2011, that Tyson will be hosting a new sequel to Carl Sagan's Cosmos: A Personal Voyage television series.

Tyson was born as the second of three children in the borough of Manhattan in New York City, but was raised in the Bronx. His mother, Sunchita Feliciano Tyson, was a gerontologist and his father, Cyril deGrasse Tyson, was a sociologist, human resource commissioner for the New York City mayor, John Lindsay, and was the first Director of HARYOU. Tyson attended the Bronx High School of Science (1972–1976, astrophysics emphasis) where he was captain of the wrestling team and was editor-in-chief of the school's Physical Science Journal. Tyson had an abiding interest in astronomy from the age of eleven, following his visit to the Hayden Planetarium at age nine. Tyson recalls that "so strong was that imprint [of the night sky] that I'm certain that I had no choice in the matter, that in fact, the universe called me." He obsessively studied astronomy in his teens, and eventually even gained some fame in the astronomy community by giving lectures on the subject at the age of fifteen.