DARK MATTER AND DARK ENERGY

Dark matter and dark energy

The surroundings we see and the materials we use contains of matter. The matter as we know is something which occupies space and has some mass, these matters contains atoms and molecules. These atoms contain particles such as protons, electrons and neutrons. In other words, we can call this matter as baryonic matter. But the interesting and shocking fact is that the matter we see i.e. the visible universe, the sun, other stars and the galaxies which contains these baryonic matters comprises less than 5% of the entire mass of the universe. The question which arises here is, what is that thing which occupies 95% of the mass of the universe?

The answer for this question is, In the entire universe baryonic matter comprise 5% of mass and the rest of the universe contains mysterious and invisible substance called dark matter (25%) and a force which counteracts gravity called dark energy (75%). This is probably the most shocking discoveries of the 20^th century. 

Let us learn about this mysterious and invisible thing in the space which we call it as dark matter and dark energy.

Dark matter

Dark matter has no particular definition, we still don’t know exactly what dark matter is but our scientists are pretty sure that it does exist because we can see the effects of it on galaxies. Scientists are not able to directly detect the dark matter as it doesn’t interact with the light and is invisible. But after a lot of study scientists have few ideas what dark matter can be, dark matter contains exotic materials which doesn’t react with the normal matter and light but still exerts a gravitational pull. The question which haunts us the most is from where do this dark matter came from, according to Dr. Stephen hawking at the beginning of the big bang, universe is thought to have zero size but as it started expanding temperature of the matter or radiation decreased. One second after big bang temp would have fallen about thousand million degrees. At this time universe would have contained particles like photons, electrons, neutrinos and their antiparticles with few protons & neutrons.

As it continued to expand and temp dropped, the rate at which electrons and anti electrons produced fell and these both annihilated with each other to form more and more photons leaving behind only few electrons. The particles which remained after this are neutrinos/anti neutrinos, these cannot be annihilated with each other as they don’t interact among themselves and with others very weakly. So, they should be still around today and it is believed that they may be in the form dark matter. But is it true or false we don’t know yet.  Now, let me tell you the effect of dark matter on some of galaxies and its stars. According to standard physics stars near edges of the spinning galaxies should move much slower than the stars near the center of the galaxy but according to recent observations stars which are present near the edges have more or less equal speed as the stars near the center of the galaxy. 

This result shows that stars near the edges are getting affected by gravitational field by unknown mass i.e. dark matter. Now, let us move on to learn about dark energy.

Dark energy

Dark energy is even more strange and mysterious, as of dark matter even dark energy has no particular definition for itself. it cant be detected, it cant be measured and it cant be tasted but we can see its effects clearly. All we know is it’s a repulsive energy which counteracts gravitational force.

 In 1929 Edwin Hubble said that light emitted from distant galaxies shifted to the red end of electromagnetic spectrum, this shift is what we call as red shift. It usually occurs because universe is expanding and wavelength of the light goes on decreasing. According to recent studies it has been seen that universe is expanding at a faster rate than what scientists expected, which is really a shocking news for them, because earlier it was believed that pull of gravity would slow down the expansion or even retract at some point and collapse on itself. The increase in the speed of expansion is due to a repulsive force present in the empty space and the interesting fact about it is, it increases as the universe expands. this invisible force is governing the expansion of the universe and is called as dark energy. sounds bit scary, right? 

The idea of dark energy dates back to 1917 when Einstein gave a cosmological constant as a mathematical aid for his static universe theory after applying general theory of relativity to it. According to Albert Einstein universe is static i.e. its not expanding and has uniform distribution of matter across the universe and is spherical in shape, to support this he gave a equation called Einstein field equation which is λ = 1/R² = κρ/2  where k is called as cosmological constant. It is a force which counteracts gravitational force, which controls or stops the collapsing of universe on itself. But later he discarded it as experiments showed that universe is continuously expanding.

 It is very interesting how ‘cosmological constant’ was called one of the biggest blunders of Einstein is now called as dark energy. Dark energy is something which is mainly found in empty space and this energy is stronger than any energy in the world. Therefore, empty space is not really empty but contains more energy than everything else combined in the universe. Till today we are unable to know what exactly dark matter and dark energy are and what are its properties. I hope we discover about it sooner and solve the mystery of it.

We think that we know everything about this universe but we are still apes holding smartphones in the tiny island called as earth in the ocean of universe.