# How much of the universe is in the form of electromagnetic radiation?

• BobiG
In summary: I cannot accurately estimate the amount of energy in the universe in terms of photons, as the number of photons is too vast. However, it should add up to a significant amount.A sun like ours looses energy in the form of electromagnetic radiation (photons) over the course of its lifetime. This energy is lost due to the emission and re-emission of photons, as well as the conversion of energy from other forms into photons. Generally speaking, the energy loss from a star is proportional to its age and size.Suns like ours loose a significant amount of energy in the form of electromagnetic radiation (photons) over the course of their lifetime. This energy is lost due to the emission and re-emission of photons, as
BobiG
Can you make an educated guess on the amount of energy in the universe in the form of electromagnetic radiation (photons), considering the vast amount of photons moving in every direction throughout the vast universe, there is literally no point in the universe that you can be in and not observe photons coming from every direction around you, meaning most of the vacuum of space has EMR moving through it. I'm guessing it should add up to a really significant portion of all the available energy in the universe? Also how much energy do you think a sun like ours looses in EMR throughout it's life time?

No, it is an insignificant amount in comparison to the energy content of the total mass content.

You can make a rough calculation from the peak energy of the cosmic background radiation (CMB), which represents the peak temperature (2.7 K) for a blackbody spectrum. For more on the CMB see:
http://abyss.uoregon.edu/~js/ast123/lectures/lec23.html

From the temperature you can calculate the energy of each photon, and then calculate the energy content per cubic meter of outer space from the density figures (~10^9 CMB photons per cubic meter).

Then compare it with the energy content of the particles in that same cubic meter - perhaps one hydrogen atom.

A good exercise in conversion of units of energy, and making physical estimates.

It's been a very long time since the universe was radiation dominated - over 13 billion years.

Photons contain about 0.01% of the energy of the universe according to the most popular modern cosmological model - the Lambda-CDM. For comparison, regular matter (baryonic matter) contains about 5%, dark matter contains about 25%, and dark energy about 70%. Other models are possible but that one seems to be the front runner at least for now. At any rate, the fraction of the universe's energy in the photons is minimal.

I must clarify that the amount of the universe in the form of electromagnetic radiation cannot be accurately determined. This is because the universe is constantly expanding and evolving, and the distribution of matter and energy is not uniform. However, it is estimated that approximately 5% of the universe is made up of ordinary matter, which includes electromagnetic radiation. This means that the majority of the universe is composed of dark matter and dark energy, which do not interact with electromagnetic radiation.

In terms of the amount of energy in the universe in the form of electromagnetic radiation, it is difficult to make an educated guess without precise measurements and calculations. However, it is safe to say that the energy in the form of photons is significant, given the vastness of the universe and the fact that photons are constantly being emitted and absorbed by various objects and particles.

Regarding the energy loss of a sun like ours in the form of electromagnetic radiation throughout its lifetime, it is estimated that our sun will lose approximately 10% of its mass in the form of energy, mostly in the form of electromagnetic radiation. This energy loss is a result of nuclear fusion reactions in the sun's core, which convert matter into energy in the form of photons. However, this amount may vary depending on the specific characteristics and lifespan of a particular sun.

## 1. How is "electromagnetic radiation" defined in the context of the universe?

Electromagnetic radiation refers to the various types of energy that travel through space in the form of electromagnetic waves. This includes all forms of light, such as radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

## 2. What percentage of the universe is made up of electromagnetic radiation?

About 99% of the observable universe is made up of electromagnetic radiation. This includes both the matter we can see and the matter we cannot see, such as dark matter and dark energy.

## 3. How is the amount of electromagnetic radiation in the universe measured?

The amount of electromagnetic radiation in the universe is measured using various telescopes and detectors that can detect different wavelengths of light. Scientists also use mathematical models and simulations to estimate the amount of radiation in the universe.

## 4. Is all of the electromagnetic radiation in the universe visible to humans?

No, only a small portion of the electromagnetic spectrum is visible to humans. The visible light spectrum is just a tiny fraction of the total range of electromagnetic radiation in the universe. Many forms of radiation, such as X-rays and gamma rays, are invisible to the human eye.

## 5. How does the amount of electromagnetic radiation in the universe impact our daily lives?

The amount of electromagnetic radiation in the universe has a significant impact on our daily lives. It is responsible for providing us with light, heat, and energy. It also plays a crucial role in many technological advancements, such as communication systems and medical imaging. However, excessive exposure to certain forms of radiation, such as UV rays, can also have negative effects on our health.

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