We all know that the eternal universe is considered an ever-expanding ball. But if it is expanding why are those changes not visible?
It’s obvious…because these changes are relative and with any change, there is a change in our frame of reference too. In this article, I plan to go deeper into this thought frame to see what can be considered absolute and what can be considered relative?
Gulliver’s travel is a famous classic which can help us analyze more of this analogy. Gulliver was thought to be a giant by the Lilliputians and after that was thought to be small with respect to the Brobdingnagian. Gulliver judged himself to be big or small with respect to a frame of reference. Here the Lilliputians and Brobdingnagians were considered to be his frame of reference. At the same time, Guliver too was a frame of reference by which the Lilliputians thought that they are small and Brobdingnanians thought they were large. Another example is asking the question regarding the size of a football. Is football large or small??
Football is obviously large compared to a cricket ball but is very small when compared to the size of the earth.
Jules Henri Poincaré was a famous mathematician who carried out the “thought experiment”. This experiment can only be imagined and visualized but not performed and tested. Consider you are fast asleep and the universe suddenly expands ten times its current size. After you get up the next morning will you be able to perceive these changes??
No!!! But why??
These changes will never be perceived by us because everything we measure is actually relative. The universe will still be exactly the same as before. Even though the universe grew 10 times larger and along with the universe everything expanded including yourself. The change still cannot be measured as along with you the scale which you use to measure your height has also expanded 10 times. This ensures your change in height to be zero. Due to this reasoning, he proposed that there is no experiment to prove this change.
Along with size, one more relative metric is time.
To put it simply, a time period of 1 year will be so long for a student completing his studies at the same time it will be nothing for a scientist or a geologist who have waited for more than 10 years for their results and progresses.
A second is considered as the time taken by a cesium 133 atom to complete 9,192,631,770 vibrations. Now imagine if everything in the universe has slowed down. Will this change be visible to us??
The answer is again no!
If everything is slowed down in-universe, so is the vibration of cesium 13 atom and so are us. Time also like size is a relative factor.
“When you sit with a nice girl for two hours you think it’s only a minute, but when you sit on a hot stove for a minute you think it’s two hours. That’s relativity.” -Albert Einstein
Like time and size, another relative term is direction. This concept can be easily visualized by considering the shape of the earth. Consider a hypothetical situation in which a person named ‘X’ lives in the North pole and a person named ‘Y’ lives in the south pole. The concept of direction will be different for both X and Y. The direction up for X will be down for Y and vice versa. This is because direction keeps earth as a frame of reference. Anything which directs away from the earth is called up whereas anything which points towards the earth is called down.
After reading all these facts, I'm sure there will be many questions in your mind such as — is motion relative? If the motion of an object is absolute then how to see if an object is moving or not without comparing it to a frame of reference? These questions are the questions that laid the foundation for the famous theory of relativity put forward by Einstein. Take a moment to think about these questions and put your thoughts in the comments!
Hope you enjoyed the article. If yes please leave a clap and if not please suggest to me some ways of improving. Thanks!!