Multiverse and Vacuum Energy Density of Our Universe
Recently, many physics theories predict that there exists not just one, but finite or infinite number of universes (multiverse). If the existence of the multiverse is confirmed, it will be one of the most significant discoveries in human history. However, even if we discover multiverse our universe will remain the most unique universe just as our Earth is unique in our universe.
Our universe is composed of 4.9% of ordinary matter, 26.8% of dark matter, and 68.3% of dark energy. Ordinary matter is all baryonic matter you perceive with your eyes or telescopes: yourself, buildings around you, earth, moon, planets, sun, and galaxies. Dark matter can not be seen with telescopes, but reveals its existence in gravitational effects on ordinary matter. The potential candidate of the dark matter is weakly interacting massive particles (WIMPs). Dark energy is also mysterious energy that works as anti-gravity and accelerates the expansion of the universe. In physics, the dark energy is equivalent to cosmological constant Λ Einstein once has added in his gravity equation. Because of this reason, modern cosmology is called as Λ-CDM model.
Composition of the universe
Currently, vacuum energy of space is regarded as dark energy. In 1928, Dirac postulated that vacuum is an infinite sea of particles with negative energy and in 1948, vacuum energy was visualized by Casimir effect. Vacuum energy density can be calculated from Hubble constant H and gravitational constant G:
Vacuum energy density = 3 x H2/8πG = 10-29 g/cm3.
If the vacuum energy density is negative, universe will contract rapidly and won't have time to produce planets, stars and galaxies. On the other hand, if the vacuum energy density is positive, universe will expand rapidly and matter won't be formed due to low matter density. However, vacuum energy density of our own universe is fine-tuned closed to zero and expands slowly to have enough time to form planets, stars, and galaxies.
Surprisingly, the vacuum energy density of our university was found to be 10120 times smaller than predicted by quantum field theory. In other words, probability of creating our universe is only 1/10120.
The number of universes predicted by string theory are 10500. Interestingly, all but one of them have negative vacuum energy density so that their universe contract rapidly as soon as they created and won't have time to form planets, stars, and galaxies. Combined probability of creating our universe predicted by both quantum field theory and string theory is only 1/10380 and virtually the same as zero and never happens in nature.
Related with the multiverse, we find some interesting verse in the Bible. The Bible says
“In the beginning God created the heavens and the earth. (Genesis 1:1)”
Here, we notice that the earth has a singular form, but the heavens have a plural form. If the multiverse is found, the Bible does describe correctly that God created numerous number of heavens (universes) but only one earth (matter found only in our universe).
We are living such an amazing and unique universe. How come we are living in such a universe whose vacuum energy density is improbably fine-tuned to positive zero?
We can't say it is a coincidence since a probability greater than 1050 never happens in nature.
It is God's great creation and masterpiece for us to live.