Time moves faster or slower depending on where you are, according to a new book by physicist Jim Al-Khalili. The book, On Time, published this week, argues that time is not an abstract concept but a real thing that can be squeezed, stretched, or twisted.
Gravity's role in time
Gravity is key to how quickly or slowly time passes. Heavy gravity means slower time, while weak gravity means quicker time. On Earth, atomic clocks show precisely 60 seconds per minute, but satellites in Earth-orbit experience fractionally less gravity, so their onboard clocks move faster than those on the ground. This is measurable and a fact.
In the 1970s, the Moon's feeble gravity meant Apollo moonwalkers' computer watches moved faster than those in Houston mission control. When the astronauts returned home, they had aged very slightly more than everyone on Earth.
Black holes and the Big Bang
The book explores further implications. A spaceman orbiting a super-dense black hole, the heaviest objects in the known universe, would hardly age compared to friends and family back home. When he returned, they would be elderly or long dead, while he still had half his lifetime left. This would actually happen.
The late Professor Stephen Hawking argued that there could not possibly be a creator. Before the Big Bang, there was no time at all. The infinitely small, dense dot of matter that would become the universe was so heavy that time simply couldn't exist. Therefore, there was no time before the Big Bang for God to have created the universe in. It popped into existence by itself, which sounds impossible but isn't to those who understand quantum physics.
