{"id":45852,"date":"2023-06-07T10:34:11","date_gmt":"2023-06-07T10:34:11","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=119029"},"modified":"2023-06-07T11:32:29","modified_gmt":"2023-06-07T11:32:29","slug":"why-does-light-have-no-mass","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/why-does-light-have-no-mass\/","title":{"rendered":"Why does light have no mass?"},"content":{"rendered":"

Why is it nothing can travel at the speed of light, but light itself can? <\/p>

By Marcus Chown\n \t\t<\/p>

Published: Wednesday, 07 June 2023 at 12:00 am<\/p>

\n\n

Einstein discovered that all forms of energy have an effective mass \u2013 ie they weigh something.<\/p>\n

Sound energy has mass, heat energy has mass, and so on.<\/p>\n

Consequently, particles of light, or photons, do have an effective mass.<\/p>\n

However, it all comes from their motion and they have no intrinsic, or \u2018rest\u2019 mass, as you or I do.<\/p>\n

This has to do with the fact that light sets the cosmic speed limit.<\/p>\n

As Einstein first recognised, no material object can ever catch up to a beam of light.<\/p>\n

Einstein discovered that as you push a body faster, more and more of the energy you put in manifests itself as mass.<\/p>\n

Moving things get more massive and by a factor \u2013 the Lorentz factor \u2013 which depends on the ratio of the speed of the body to that of light.<\/p>\n

You would need an infinite amount of energy to push a material body to the speed of light, so the speed of light<\/a> is forever unreachable.<\/p>\n

The exception is if the object has no rest mass to start with. Multiplying zero by any factor equals zero.<\/p>\n

So photons \u2013 and any other particles with zero rest mass \u2013 can travel at the speed <\/span>of light.<\/p>\n

Ultimately, we have no idea why there is a speed limit set by the speed of light and why, for instance, we don\u2019t live in a Universe where things can travel at infinite speed.<\/span><\/p> <\/body><\/html>\n

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