If so, what exactly is it that it is travelling through? Or does time itself do the moving and is constantly sweeping past us like the wind while everything else stands still? Does time actually exist as anything or is it just a convenient invention to allow us to talk about how things are moving? To answer this question — or ask a new one — email lastword newscientist. Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style.
Please include a postal address, daytime telephone number and email address. New Scientist Ltd retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format. Trending Latest Video Free. In electromagnetism, we know that Maxwell's equations govern electromagnetic radiation. From Maxwell's equations you can derive the EM wave equation. As the quanta of these waves, photons will also travel at light speed.
Photons are massless, but they have finite energy. Because photons are light quanta. So the claim 'photons travel at the speed of light' is the same as or the quantum counterpart of 'light travel at the speed of light'. It is almost by definition, that is, by definition and by the fact that photons are light quanta.
The electromagnetic wave travels at speed of light which is explained by Maxwell's equations. However, in many cases, electromagnetic wave can also exhibit the particle-like behaviour wave-particle duality , e. Einstein's photoelectric effect, so physicists have to model it as particle, known as photons. So what we know as electromagnetic wave is also particle with common property, i. Both theories are correct and we don't know exactly what "it" really is.
In summary, photon is just a model for explaining when electromagnetic wave behaves like particle. Asking why photon travels with speed of light is the same as asking why electromagnetic wave travels with speed of light. As other answers have mentioned light in classical electricity and magnetism is described very well by the solutions of Maxwell's equations which combine electrostatics and magnetism and describe a traveling wave of energy propagating at a speed c.
This speed is not arbitrary but, as it comes out from the equations, depends on the electric and magnetic constants of materials or the vacuum:. Photons on the other hand are elementary particles and are necessary at the basic framework where quantum mechanics is the description of nature. Photons appear in elementary and nuclear interactions, taking away energy and momentum and are seen in subsequent interactions giving up their energy and momentum. As a particle at that level it is also a wave, and there exist consistent derivations of the formation of the classical wave from a large ensemble of photons.
Light travels as a wave and interacts as a particle so there seems to be no way to answer the question. For example, consider a gong.
When you strike the gong, sound propagates though air. Photons are the end result of gamma radiation. When you 'bang a gong' that energy is released. Same as with light energy or photons. Photons, i. It is not because of theory. Therefore if a wave is created in such a region, it must be created right at the wave speed of that region. This is not just a quantum concept. It applies to all waves, from seismic waves, ocean waves, and sound waves, to waves on a piano string.
Some people say that the reason a photon travels at light speed the moment it is created is because it is a massless particle, and therefore must always travel at the speed of light. While it is true that the photon is massless and therefore always travels at c in all reference frames, this is not the reason that it is created already having a speed.
The reason is simply because it is a wave. Other quantum objects such as the electron do have mass, and they have no problem being created at some non-zero speed without ever needing to be accelerated to this speed.
All quantum objects are partly waves and therefore can have a speed the moment they are created. For example, a free neutron eventually decays to a proton and creates an electron and an anti-neutrino in the process. This decay has been observed experimentally many times. The electron that is created in this process zips off at a certain speed that it has the moment it is created, without ever being accelerated.
0コメント