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Is light matter?
Question Date: 2014-09-04
Answer 1:

This is an interesting and rather complicated question. The short answer is no, but it can interact with matter. When you pluck a string, you cause a vibration or wave in the string. The string doesn’t gain or lose matter in this process, it just moves. Similarly, the entire universe has what is called an “electromagnetic field” and when that is “plucked” it creates light. Electrically charged objects are responsible for this field and are affected by it. So in a sense, light is just a vibration in this “force field” that affects matter. Another way to think about light is as “photons” which are little packets of light that have similar properties to matter, but still aren’t matter. In summary, light is not matter, but sometimes it is useful to think of it as matter.

Answer 2:

No, light is not matter. It is energy. However, you may have heard that light can sometimes act like a particle. This is because the energy travels in bundles called photons. Theoretically, you could even count these photon bundles. But each photon is an energy bundle and not a matter bundle.

Answer 3:

This is one of the fundamental questions of the last 100 years of physics. Quantum mechanics says that light has some of the same properties as matter, but it is not matter. Light is carried in tiny particles called photons, but, unlike matter, photons do not have mass or volume. In that way light behaves more like a wave, such as from your microwave. This is a very complicated concept called "wave-particle duality" and physicists have worked on it for decades. Since matter must have mass and volume, though, and light has neither, it is not matter.

Answer 4:

Matter has mass.

The longer answer is there is a lot of jargon and philosophical questions involved with the definition of light and matter.

You may have heard about the mass – energy equivalence developed by Albert Einstein [1].

E = m c 2

This equation is saying mass, m, multiplied by the speed of light, c, squared is an energy, E.

Please note that m in E = m c 2 is the mass of an object.

There are some deep physical questions associated with your inquiry. Particularly how can we equate light and mass? Can we show the results in an experiment? A lot of progress was made in the 20th century answering these questions in the field of high energy particle physics.

I am going to leave you with a fundamental law of physics and an experiment. Energy can neither be created nor destroyed, it can just be changed from one form to another. It is possible for the mass of two objects to decrease when collided because some energy is emitted in a photon. Rest mass energy was changed into electro-magnetic energy. Please see equations 8 and 9 of the source cited.

[1] Fernflores, Francisco, "The Equivalence of Mass and Energy", The Stanford Encyclopedia of Philosophy (Spring 2012 Edition), Edward N. Zalta (ed.), link = click here to read.

Answer 5:

No; light is free energy. Matter has mass when at rest, which light does not.

Answer 6:

The most common definition of matter is "anything that has mass and occupies space". Following this definition, light is not considered to be matter because it does not have mass and does not occupy any quantifiable amount of space.

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