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Name: Mike T.
Status: other
Age: 30s
Location: N/A
Country: N/A
Date: 2001-2002

How do emitted photons instantaneously travel at the speed of light since they were not accelerated? At one instant there is no photon, and at the next instant, it miraculously is already travelling at the speed of light.

Hi, Mike !!

A photon - as you know - is an electromagnetic (EM) wave . Its energy is described by e = h. n in a quantum of energy. All EM waves travel in the vacuum with the speed of light. A photon is a form of energy and results from transformations of another forms of energy. When the photon appears it behaves like all EM waves. It doest need to be accelerated. All bodies emit EM waves, even a peace of ice. The question concerns more on the frequency. If you see the light - visible light - it covers a range of wave length between 400 and 700 nanometers.

When you mention in your question that "...emitted photons instantaneously travel at speed of light and were not accelerated..." than you are thinking like a particle behaviour that needs to be accelerated, right ?? Than, we find ourselves at the hands of the problem concerning to the dual behaviour particle-wave of matter. You are thinking of particle and making a question for waves...Waves do not need to be accelerated. Particles do, but we are talking about wave-photons, arent we ?? And - besides of that - photons are generally regarded as particles with zero mass and no electric charge...( again the dual behaviour of matter ).

Alcir Grohmann

This is not an easy question and is not treated in introductory spectroscopic texts or quantum mechanical texts, at least the ones I could find. It involves time dependent quantum mechanics. The best treatment I have been able to find so far is on the web site:

Vince Calder


Newton's laws of physics do not apply to objects moving near the speed of light, or to objects smaller than an atom. Small scale requires quantum physics. Large speed requires relativity. Light fits both criteria. Also, light photons have zero mass. This is another fact that makes them unusual.

At the level of quantum physics, things change form at almost random times. You cannot predict where something will be. You can only say it has a probability of being somewhere. Objects under the right conditions can change into other objects without being forced to. A photon flying through space can change into an electron and anti-electron, or vice-versa. Quantities such as total momentum, total energy, and total electric charge must be conserved, but many things can change. We do not know how or why it happens.

We can deal with a bundle of millions of particles, working with average effects (a baseball is millions of protons, neutrons, and electrons; a beam of light is millions of photons). We do not know how an individual particle works. We do not know what actually happens during the process of changing, only before and after. We don't know whether it requires any time at all. It is almost like a change of reality, switching between a universe with a photon and a universe with an electron and anti-electron.

Dr. Ken Mellendorf
Illinois Central College

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