Time - Fact Talk #5

Time is a indefinite continuous progress of existence and events that occur in an apparently irreversible succession from the past, through the present, into the future. Time is refer as a fourth dimension. Investigations into the relationship between space and time led physicists to define the spacetime continuum.

Time is relative

Time passes faster for your face than for your feet (assuming you're standing up). Einstein's theory of relativity dictates that the closer you are to the centre of the Earth, the slower time goes – and this has been measured. At the top of Mount Everest, a year would be about 15 microseconds shorter than at sea level.

First there is 370 days in year

When the dinosaurs were alive, there were 370 days in a year. The Earth's spin is getting slower because the moon's gravity is acting as a drag, so days are getting longer, by about 1.7 milliseconds per century.

Smallest measure of time

The smallest standard scientific measure of time is the "Planck time". It takes you about five hundred and fifty thousand trillion trillion trillion Planck times to blink once, quickly.

There is no "Now"

There's no such thing as "now" as far as physics is concerned. Space and time are fluid, affected by gravity and your speed. Einstein put it like this: "For us physicists, the distinction between past, present and future is only an illusion, however persistent."

Everything we see is past

Because light takes time to reach us, everything we see is in the past. The sun you can see out of the window is 8 minutes and 20 seconds old. The light from our nearest star, Proxima Centauri, is 4 years old.

Time get slow if you move fast

Time passes slower the faster you move. If you flew to the star Sirius at 99% of the speed of light, then flew back again, the people you left behind on Earth would have aged more than 17 years. But you would have aged less than two and a half years.

Most accurate clock

The most accurate clock ever built is the strontium clock, which is accurate to within a second over 15 billion years.

The oldest object on earth

The oldest known object on Earth is a 4.4-billion-year-old crystal, a zircon, that was found in Jack Hills in Western Australia. It's only 160 million years younger than the Earth itself.