The rate of expansion of the universe is increasing however, scientists have no explanation of why. The force of gravity should be slowing it down, but we have concluded that there must be some other energy in the universe causing this expansion to accelerate.
What is energy?
Energy can be in a range of different forms and can be defined as the capacity of a physical system to perform work. Einstein’s equation E=mc2 tells us that matter and energy are more closely related than initially believed. Mass can be converted to energy, for example in the Sun through nuclear fusion.
Before the 1990s, scientists believed that the rate of the expansion of the universe would be slowing down due to the effects of gravity. However, a discovery in 1997 changed this entirely.
Brian Schmidt and his team in Australia were attempting to calculate positions of supernovae, but the results suggested they were further away than first predicted. This suggested that the rate of expansion of the universe was not slowing as expected but actually accelerating.
Still unsure what is preventing gravity from slowing the expansion, the current explanation scientists have given is something called dark energy.
Energy of space
Dark energy remains a mystery still today, but we think that about 70% of the universe is made up of dark energy. Despite accounting for such a large amount of the universe, we still don’t know what it actually is.
One of the current theories is that empty space actually contains energy. This contradicts our current understanding that energy must have some source – matter or radiation. We do not know where this energy would come from, but if this theory is correct it may solve the problem.
As the universe expands, more empty space will be created and therefore more dark energy also. This provides more energy for the universe to expand at a faster rate. However, we don’t know why or how this would arise.
A new field?
Another suggestion is that dark energy is actually another fundamental force and its energy field fills the whole of space. This field would have the opposite effect to matter on the expansion of the universe. However, the mystery remains as to why it exists or how it interacts.
Is Einstein Wrong?
The other explanation for dark energy is that it doesn’t even exist, instead Einstein’s theory of gravitation is wrong. A new theory of gravity could explain both why the universe is expanding faster but also the way matter behaves in galaxies. This would remove the need for dark matter as well.
However, the problem with this is that a new theory of gravity would be required. Einstein’s theory explains the motion of planets in the solar system and in most other cases it also works. Therefore, we believe that Einstein is correct but perhaps his theory needs to be modified slightly.
An unsolved mystery
Dark energy is thought to make up 70% of the universe, and the fact we don’t even know what it is shows that we currently have a big gap in our fundamental understanding of the universe. This leaves the possibility for our current understanding of physics to be modified as scientists make breakthroughs in this field of study.