Spacetime behaves as a medium of light – Thought Experiment

Spacetime behaves as a medium of light – Thought Experiment

Spacetime: So today I am going to talk about an awesome concept of theoretical physics called “Medium of Light”. The medium of light means the medium in which the propagation of light is possible.


This topic is also considered the most challenging concept in physics just like the Constancy of the Speed of Light. In this article, we are not going to consider air, vacuum, and ether as a medium of light perhaps we will consider it the Fabric of Spacetime.


At the end of this article, we will understand the complete information about light, the history of the medium, and also what is the medium of light.

So let’s Start:-

What is Medium in Physics?

Medium is a special type of group of substances, due to which a wave or particle travel from one place to another. Nothing can go from place to place without a medium.


For example:- 

  1. Sound Waves

Sound waves mainly used Air as a medium. Now Air is made up of different-different elements and molecules like- H2, O2, N3, and Co2, etc. And we knew that “a wave travels through the disturbance of particles in a medium”. It means the sound we hear is reaching us by the complete disturbance of particles in a medium in their path.


  1. String Waves

String Waves used string as a medium to travel.

Types of Medium

Mainly there are two types of medium exist in theoretical physics they are:-

  1. Rarer Medium

  2. Denser Medium

Rarer Medium:-

The medium in which the particles are distant from each other is called the Rarer medium. For example Air etc. In this medium waves need more time to travel because for easy disturbance particles should be close to each other in the medium.

Denser Medium:-

The medium in which the particles are close to each other is called the Denser Medium. For example Water, Honey, Glass, and any Solid substances, etc. Waves travel faster in the denser medium as compared to the rarer medium.


Sound Waves are faster in water as compared to air due to the above explanation.

What is Light in Physics?

Light is an electromagnetic wave that operates as a result of the vibration of electric and magnetic fields, like other electromagnetic waves. And it is made of photons.

And the thing that makes light different in all these electromagnetic waves is its visibility. We can see only one electromagnetic wave and that is Light Waves. This is due to the fact that the light waves are made up of different-different colors, we cannot see light in combined color form because it is white. But due to changes in wavelength, White Light distributes in different-different colors, and these colors are completely visible to the naked eyes.

The most unusual property of light is its duality. Till now, there are many people who think that “the light comes from the outer space, it means the vacuum is the medium of light”. But I want to tell them that a vacuum is the absence of air, not a medium like air. It means there is something in outer space that propagates light waves through them. 

Light Spectrum

When white light passes through a prism, then its component is divided into different colors. These divided colors are of 7 types(as seen in the image). They are Violet, Indigo, Blue, Green, Yellow, Orange, and Red. These colors are called bends of colors and this bend is called Spectrum of Light.


Dual Properties of Light

1. Wave Nature of Light

In the year 1864, When James Clerk Maxwell published hisDynamical Theory of the Electromagnetic Field, then we came to know that “Light shows Interference which is the property of a wave”. In this way, people and scientists believed that light is a wave for another 41 years(1864-1905).

2. Particle Nature of Light

In the year 1905, When Albert Einstein(one of my favorite physicists) published his concept of the Photoelectric Effect, then we came to know that “not only wave nature, the light also shows particle nature”. In this way, after 1905 everyone believed light has Dual Nature(Wave as well as Particle).

The Things You Should Know About Light:-

  • The rest mass of light(photon) is zero and its relativistic mass is undefined.
  • The light and all other electromagnetic waves in a vacuum or air medium(this is not a real medium of waves) are 299,792,458 meters per second(approximately 300,000 km/s).
  • Speed of Light is called Speed Limit of the Entire Universe according to the Special Theory of Relativity.
  • The frequency range of visible light is 4 × 1014 to 8 × 1014 Hz
  • The wavelength range of visible light is 380 to 740 nanometers.
  • Directly and indirectly, all energies on earth come from the sun in the form of light waves.
  • All waves include Light have momentum without rest mass, they carry the energy and are always in motion

What is the History of the Medium of Light?

The Luminiferous Ether:-

In the 19th century, when people came to know the light is a wave then Scientists started raising the question that if the light is a wave, then in which medium is it traveling like other waves? 

Nothing was known about this medium, due to which it was named as the Luminiferous Ether. Before the end of the 19th century, everyone believed that light rays travel in this hypothetical medium called Luminiferous Ether.

But two American physicists Albert Michelson and Edward Morley trying to prove the existence of this hypothetical medium in the year 1887. But the result was surprising that light does not need any medium like Ether for traveling in space.

What is the Medium of Light?

Spacetime as a Medium of Light:-

I don’t mind what others think of me, but it would be right to consider the medium of the light as spacetime. Because according to Albert Einstein or his General Theory of Relativity that gravity bends the fabric of spacetime, due to which the direction of light rays also changes. It means that Light Rays travel through something called Spacetime.

That’s why here I consider Spacetime as a Medium of Light. And it is everywhere in the air, water, matter, solid medium, and even inside an atom maybe except for the nucleus.

Question 1:-

Here a most difficult question generated:- If Spacetime is everywhere even inside us then why light doesn’t travel through us?

Its answer is too easy for me that as compared to liquid material the separation between particles in a solid material is very low. Due to which the frequency of light waves and their wavelength prevents them to enter inside a solid object. 

This is the cause due to which light waves just collide with the surface. And it is also Scientific Proved – the concept of the photoelectric effect tells us that as soon as the light hits a metal surface, then the electron of an atom in the metal surface gets polarized, and this causes the emission of electrons from the metal surface. So this shows us that light waves can only go on the surface of solid objects.

But there are also some other electromagnetic waves such as the X-Rays and Gamma Rays whose frequencies are very high, due to which such waves can go inside our body. And I don’t need to prove it because everybody knows it.

Question 2:-

Another Question: If Light doesn’t go inside a solid medium then why it easily travels through Glass(Solid)?

We will easily know the answer to this question if we understand “what this glass?”.

So let’s start

What is Glass?

Glass is a super-cooled liquid that is made of silicon dioxide and some impurities and has no internal boundary. This means that in reality, the glass is a liquid that is strongly cooled and made solid at room temperature.

So the density of molecules low in Glass like water, due to which the light rays easily travel through glass.


What we have learned:-

  • Everything needs a medium to travel from one place to another whether it is a way or a particle.

  • Light is an electromagnetic wave and the medium of light waves is Spacetime.

  • Light rays can only go on the surface of solid object except for glass medium(because it is a supercooled liquid)


This is everything about light

Thanks for reading

If you have any questions, ask me by comment.

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How did Edwin Hubble discover the Expanding Universe?


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