Birthdays & Relativity

Hasn’t it made you wonder once why we even celebrate birthdays ? I’m not trying to be a pessimistic party pooper here, but seriously, it all started somewhere when we created calendars and started noting down “Birth” days, a day when we were born. But for the thousands of years before that, calendars never even existed, time was just a dimension, and was never a human perception. Birthdays were just another day.

Birthday history

It all started in Ancient Egypt, where they used to celebrate the birthdays of the pharaohs, not their actual biological birth though, but their rebirth into Gods. Egyptian pharaohs are said to transcend into Gods, and that was their actual birthday, a birthday of a God.
Time went by, the Greeks took this celebration from the Egyptians, the Romans took it from the Greeks, and cultures basically mixed together and so did the meaning of the celebration until we commonly know it today as the date a person was born according to the Gregorian calendar, a day where we praise the birth of a beloved, and send him/her sincere wishes of prosperity and success and good health in his/her future ventures.

But what is it are we really trying celebrate here ? The day we were born ? And if so, how do we mark this special day ?

Time and Relativity

Time is an important parameter for any celebration/remembrance . Birthdays, anniversaries, independence days, Christmas… all of which are annual celebrations that require a notion of time. And that’s of no surprise of course, because they occur, well.. annually. That means every 365 days, every time the Earth revolves around the Sun once, we remember something. Strange isn’t it ? How we have associated a motion of a rocky planet around its star to our memory.

But this is all made up, isn’t it ? Kind of yes. Time, in our human use, is a concept we have created to keep track of our activities, a way to be more organised. Why is a year 365 days, and why is a day 24 hours, and a week being 7 days? All these numbers seem to have come from somewhere no? This history behind these numbers is not magical, it is attributed to us having by 10 fingers, and the base or radix we use, and the fact we have 1 moon which has 12 lunar cycles a year, and lots of other reasons that inspired us or more like “paved the way” for us to use such numbers. So it is a very personal usage of numbers, and it is by no means a divine rule or a universal physical law. It is purely relative to us and only us, humans.

For someone who lived up to 80 years, this means that this person has lived on Earth as it completed 80 revolutions around the sun. So what if this person were to be on a faster planet ? A planet that revolves twice as fast as our Earth does around the sun, does this mean I will live up to 40 years only ? Well no not really, your biological clock has got nothing to do with where you are or how fast you move. All we have did here is defined a new basis for our time measurement, instead of 1 Year = 1 Earth revolution, we now have 1 Year = 1 Planet X revolution.

However, that’s not the end of the story. For simplicity now, let’s assume Planet X has the same mass density as Earth, and the Star that Planet X revolves around also has the same mass density as the Sun. As before, your biological clock won’t change between the two planets, if you are able to celebrate your birthday 80 times on Earth, you will also be able to do the same on Planet X, but the only difference here is that you would celebrate them faster on Earth than on Planet X, as compared to an inertial frame. The reason behind this is due to what is known as Gravitational Time Dilation, a general relativistic effect that says that clocks in a stronger gravitational field tick slower. If both Earth an Planet X have the same properties and revolve around the same star, but Planet X revolve faster, then the only possibility is that Planet X is in a stronger gravitational field than Earth’s, and hence clocks on Planet X tick slower.
Let’s say you have a twin sibling on Planet X while you’re on Earth, if you just celebrated your 24th birthday and decided to visit your twin on Planet X, you could actually make it in time for your sibling’s 24th birthday as well!

As mind boggling this idea is, as true as it can get. It took me a while to get my head around it, and it added more ambiguity to my concept of time at first, but became clear when you come to think of time as a dimension same as space, together as one, namely spacetime.

Time is a Place

Have you abandoned your old concept of time now ? Good. Now as every second passes by, we have moved somewhere new in the universe, to a place on a our extended 4 dimensional map called spacetime. So from now on, it is more accurate to say “I was 23 when I was IN 2019 at home on Earth” rather than saying ” Last year I turned 23″, the latter takes a lot of information away, mainly “where were you last year” ? and by “where” here I mean where in spacetime, not just in space. That is why the first statement is very accurate, and much more beautiful, because now your birthday isn’t just a day in a meaningless calendar we created, it is also your eternal birthplace in the universe.