Physics

A time travel… about TIME!

“We have to take into account that all our judgments in which time
plays a part are always judgments of simultaneous events.
If, for instance, I say, “That train arrives here at 7 o’clock,”
I mean something like this: “The pointing of the small hand of my watch
to 7 and the arrival of the train are simultaneous events.”

Hi guys!

Have your summer holidays already started?

Do you have that  feeling, too, of losing the sense of time when school finishes and we don’t have any more written or oral tests to do?

When I’m on holiday, there aren’t many differences between Mondays and Saturdays!

But…what is actually TIME? I think that this is one of the most difficult questions that lots of philosophers and scientists have asked themselves over centuries.
First of all, Aristotle (as Newton) believed that time was absolute and independent from the concept of space: if we have a good clock, we can work out the interval between two events.
The Danish astronomer Ole Romer discovered that light travels at a finite speed; observing the delays of the eclipses of Jupiter’s satellites, he noticed that they depended on the distance between our planet and Jupiter; in particular, the bigger the distance, the greater the delay.

Years later, Maxwell stated that light waves travelled at a fixed speed; but what did this speed have to be measured in relation to?

For this reason scientists hypothesized the existence of ether, a substance present everywhere, even in space. So light travelled at a fixed light in relation to ether, but if two different observers were moving, they would obviously find two different results.
However, Albert Michelson and Edward Morley discovered that if we work out the speed of light from the Earth, we find the same results, in spite of its revolution.

Oh no! What was wrong again?! The concept of ether is useless, as Albert Einstein would explain later: according to his theory of relativity, scientific laws don’t depend on the speed of the observer, but they’re always valid; from this idea derives the equivalence between mass and energy and the scientific law that no object can be faster than light.

This means that the concept of time can’t be absolute: if the two poor observers are looking forward to measuring the speed of light when it covers different distances, time will be different in spite of their watches (since speed is the quotient between distance and time and it has to be constant)! This means that time is NOT separated or independent from space, but they form another entity called space-time; moreover, this is the reason why scientists are used to saying “that star is light years far from us”.

If we have to describe an event, we need four coordinates: three are spatial and one is temporal. We can compare a light impulse to a stone thrown in a pond: it sinks creating bigger and bigger circles as the water waves spread through rings. The result is a three-dimensional cone in the four-dimensional space-time. Perhaps some of you will think that I’m “waffling”, but an image will convince you!

On one side there are all the events that could be influenced by a present event; on the other side there are all the events that could influence what happens in a present event.

I’m not “specialized” in these strange concepts, and I still have many doubts and question marks in my head.

However, I hope I’ve passed on my enthusiasm to you and, above all, I’ve not confused you! 😉

Enjoy yourselves this summer!

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