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Is the Energy of the Universe really constant?

Last updated on September 3rd, 2020 at 04:57 pm

‘Energy can neither be created nor can it be destroyed. It can only be transformed from one form to the other.’
We are told that this is a fundamental law of the universe, but what if this law is not that fundamental as we see it. Ever given a thought to it? Why does energy have to be constant?

This law was founded in the earliest era of physics as we know it. And back then, physicists considered the laws of the universe to be constant with time. In more precise terms time-invariance of the laws of physics was considered to hold true. And it perfectly makes sense if you think about it if you throw a ball now and after a billion years what should be the difference between the laws that govern the motion of that ball? So in daily interactions, we never come across with violation of these laws, but there are cosmological exceptions.

It all began in1915 when Emmy Noether provided the logical reasoning for the energies of the universe not being constant, we assumed time symmetry and derived the conservation laws but as it turns out time symmetry can be broken. After that thanks to general relativity, we now know that the universe is expanding i.e. the fabric of spacetime is expanding and everything on it is moving away from each other at an accelerating rate. So if spacetime is not constant but changing, then how can energy be constant?

Cosmological redshifting:-

As light waves move away from us, they elongate and shift into lower frequencies. UNIVERSAL HISTORY ARCHIVE/UIG VIA GETTY IMAGES

The effect of expansion of the universe on light is termed as cosmological redshifting, This effect is quite similar to the Doppler redshifting of light wherein the wavelength of light changes due to the relative motion of the source and the observer but in this case, the light is stretched out due to the expansion and not the relative motion.

The stretching of the waves causes its wavelength to increase and thus the term redshifting. The increase in wavelength leads to a loss of energy. The question that now arises is where does the lost energy of the waves go. The answer is yet to be found.

Some theories suggest it’s related to dark energy, others say that the work done in the expansion of spacetime requires energy and this energy is used against the gravitational potential increase of the system. Another interesting theory is that it is used in maintaining the vacuum energy density of the expanding universe.

One possibility is the energy is lost after all the energy is not constant. There is no evidence (until now) to prove that this is wrong. But the thing is we might be asking the wrong question to discuss the conservation of a quantity we should know it first!

What is energy?

We define energy as ‘The capacity to do work or produce heat’. This is not a definition it’s the modes of transfer of energy. The main problem is there is no specific definition of energy. Even the theory of relativity doesn’t give a precise definition of it.W e are now hoping that the incomplete theory of quantum gravity may give us the answer to our question.

‘It is important to realize that in physics today, we have no knowledge of what energy is’ -Richard P. Feynman

We can say that more research needs to be done on the topic. This is the edge of it. The more we know the more there is to explore, in the words of Albert Einstein, “As our circle of knowledge expands, so does the circumference of darkness surrounding it.”

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Jus Jaisinghani is an undergraduate in Manufacturing Science and Engineering at IIT Kharagpur. He is a Physics and Space science enthusiast.

Jus Jaisinghani is an undergraduate in Manufacturing Science and Engineering at IIT Kharagpur. He is a Physics and Space science enthusiast.



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