Planck units.

How old is our body?

This might seem very absurd to ask how old we are. We would immediately say the time passed since we took our first breath. However, we are made of trillions of cells which are further made of atoms and molecules.   

 The atoms in our bodies are quite old. We eat food which is broken down in smaller molecules which is absorbed by our body. The atoms transfer energy from food to us. The foods we eat get the energy from the soil where they are grown and so on. The growth of any living thing represents the accumulation of these atoms. So the question is how did the soil get these atoms.

The age of the earth-

Our earth is approximately 4.54 billion years old. The earth was created from the Sun, which is all sources of energy to any life on earth. So you may think if the earth was created from the sun then both should have the same composition but it is not true. The sun is made of mostly a single proton atom that is hydrogen. Because of the enormous mass of the sun, the hydrogen atoms in the core are crushed together. The pressure at the center is so high that the protons from hydrogen atoms merge together to form heavier atom helium. 

For an analogy, the pressure at the center of the sun is approximately 1575x10^9 kg per square inch. The mass of the heavier atoms is not the same as that of the individual masses of hydrogens, It is because some energy is released during this process. Here you may wonder how energy released can effect mass, this is the creative discovery by Albert Einstein that is energy and mass are related and given by the equation E=mc^2, where c is the speed of light which is universally constant. This is one of the great discoveries of Einstein. When the earth was created it was very hot and in a plasma state. Its temperature reduced slowly but the core was still too hot. The pressure at the core of the earth is very high that results in creating heavier elements and compounds like iron, Nickle, etc.

                                                    source: https://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/Sun_poster.svg/640px-Sun_poster.svg.png

The Universe

Our universe is nearly 13.7 billion years old and it is continuously expanding since the big bang event. Today the universe is so so big that its diameter reaches about 93billion light-year across. But once our universe was unimaginably small. It was about 10^23 times smaller than an H atom, which is way too small, we can not imagine something that small. This is known as plank length which is the smallest possible distance in the universe possible. When the universe was of size one Planck length, it was one Planck time old(10^-43 sec) and one plank temperature hot(10^42 K). These are the smallest things in the universe.

These values were derived from 3 fundamental constants of the universe 

    1. G - the gravitational constant, given by sir Issac newton and calculated by Henry Cavendish.

    2. c - the speed of light, given by Albert Einstein.

    3. h - Planck constant, given by Max Planck.

Planck length(the smallest length possible in the universe ) = 

Plank time(smallest time possible that can be measured) = 

Plank temperature(the maximum possible temperature in the universe) =

where ħ = h/2π

2π

So what is the significance of Plank length?

It is the smallest possible distance where the gravity would have an effect. It is also believed that at this scale the spacetime itself is quantized. So this is how quantum physics can be described, the study of the smallest possible thing which has a physical meaning.