The ‘light’ that we now ‘see’ as beautiful nebulae from exploded supernovae will also die out one day. Also the pulsars, what about the ‘standard candles’ on the gold plate in the Voyager to ‘show our place in the universe, but by then our solar system will no longer exist and ‘they’ won’t be able to find us anyway. The radio waves emitted (already 70 years long) from the earth will also be extinguished in the universe and if they collide with something (much further than the moon) they can be sent back to earth? The microbes that have survived the vacuum and the radiation in space, have their DNA not changed and can’t ‘new species’ arise? But are they kept in strict isolation?
Answer
The light that is emitted into the universe does indeed die out when it is absorbed by something, and not reflected. But that light then releases its energy to the body that absorbs it, and can therefore be re-emitted as radiation. It never completely goes out, because energy is never lost. The law of conservation of energy is an essential basic law of physics, and as such has always been affirmed.
If the light doesn’t meet anything on its way, it just keeps going. How far along the way that happens, therefore, depends on how much matter it encounters or not along the way, and also on the wavelength of the light (long-wavelength radiation travels further). When we see nebulae, in visible light, in the thousands of years that their light travels, typically a few tens of percent of the way has already been absorbed by the interstellar dust and gas. But the afterglow of the big bang, which has been underway for more than 13 billion years, we still ‘see’ (in quotes, because it’s about radio waves) coming towards us for more than 90%.
Those 13 billion years are small relative to infinity anyway, and in an infinitely long universe no radiation can hope to survive forever. But the energy it gives off when it disappears causes new processes elsewhere, which in turn radiate energy.
![Will the ‘light’ we now ‘see’ in the universe all fade to nothing? Will the ‘light’ we now ‘see’ in the universe all fade to nothing?](https://www.ikhebeenvraag.be/mediastorage/FSImage/A0/3993/christoffel_waelkens_kuleuven.jpg)
Answered by
prof. Christopher Waelkens
Astronomy
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