# The Naked Scientists Forum

### Author Topic: Does light wear out? And how far can it travel?  (Read 1541 times)

#### thedoc

• Sr. Member
• Posts: 511
• Thanked: 12 times
##### Does light wear out? And how far can it travel?
« on: 12/01/2016 14:47:40 »
One question asked in my primary science class, when learning about energy, is 'when does light wear out?' and 'how far does light travel?' and I am unsure how to accurately.  Can you help?

Visit the webpage for the podcast in which this question is answered.

« Last Edit: 12/01/2016 14:47:40 by _system »

#### Space Flow

• Sr. Member
• Posts: 400
• Thanked: 31 times
##### Re: How far does light travel?
« Reply #1 on: 05/12/2015 03:08:45 »
Theoretically Light travels for ever. Its Wavelength gets stretched and made longer by the expansion of spacetime but can not be seen to reach DC. Given enough time and a non-expanding Universe you could have said that it would be limited to the Diameter of such a Universe.
Us living in an expanding Universe, have unlimited length for light to be stretched to and still represent one cycle.
Detecting light when it gets stretched to extremes is a different question.
So far the oldest light we can detect is of course younger than our Universe.
It has a long way to go before it gets stretched anywhere near the wavelength of our Observable Universe.
Past that there would be no way for us to have an antenna long enough to detect it. Theoretically it would still be there.
« Last Edit: 05/12/2015 03:20:56 by Space Flow »

#### chintan

• Jr. Member
• Posts: 19
• Thanked: 1 times
##### Re: How far does light travel?
« Reply #2 on: 05/12/2015 06:47:52 »
Quote
One question in my primary science class learning about energy is 'when does light wear out?' and 'How far does light travel?' and I am unsure how to accurately and simply answer these questions.  Can u help?
What do you think?
U can say that light does not have edges but it gradually fades as radiation decreases and then u can't see any visible end
« Last Edit: 05/12/2015 06:53:42 by chintan »

#### evan_au

• Neilep Level Member
• Posts: 4130
• Thanked: 249 times
##### Re: How far does light travel?
« Reply #3 on: 05/12/2015 08:55:12 »
Quote from: chintan
This is referring to the "Inverse square Law", which states that if you go twice as far from a light source, it appears 4 times dimmer.

The reason for this is that the particles of light ("photons") travel in pretty much straight lines, and are spread out over a larger area the farther they travel.

But the individual photons don't fade away - you just need a bigger telescope to collect enough of them.

Quote from: Sandy
'How far does light travel?'
Photons just keep going until they run into something and are absorbed (or they can be reflected or refracted too).

Quote
when does light wear out?

Space Flow correctly points out that light is red-shifted by the expansion of the universe, so an individual photon is received with significantly less energy after it has traveled most of the way across the universe.

The following users thanked this post: jeffreyH

#### thedoc

• Sr. Member
• Posts: 511
• Thanked: 12 times
##### Hear the answer to this question on our show
« Reply #4 on: 12/01/2016 16:32:49 »
We discussed this question on our  show
Kat Arney put this question to physicist Stuart Higgins...
Stuart - The short answer is - no it doesn't wear out. It never wears out, it keeps travelling for ever and that's because light actually is a wave of energy, it doesn't have mass, and so things that have mass, normally decay into smaller things and break down. In this case light doesn't have it. It will just keep going for ever. However, that doesn't really match our everyday experience. If I shine a torch in your eyes and it's blindingly bright, and then I stand the other side of a field and shine it towards you, it looks dimmer, it doesn't seem as bright, so what's going on there? There's different things that actually that could make light wear out as it were, and that's where the light might be absorbed by the particles of the air, or the atmosphere, or scattered off the dust. Or it might be the lights just not reaching you, it's shooting at a slightly different angle.
Kat - So, if there was a perfect vacuum in the field between you with the torch and me, then it would seem as bright as if I was standing right next to you.
Stuart - Not quite. So if it were maybe a laser, and the laser was shining and the laser travelling in a straight line, that would be fine but, actually, the torch, if you think where the lights being made by the filament, it passes through a lens, that scatters some of the light, it passes through. There's usually a bit of metallic foil in their as well that kind of pushes it toward the front of the torch, but even still the light is spreading out and so, if you imagine the number of photons that are reaching your eye, it's actually decreasing the further away you are as your eye is only a fixed area that can receive them.

Click to visit the show page for the podcast in which this question is answered. Alternatively, listen to the answer now or [download as MP3]
« Last Edit: 01/01/1970 01:00:00 by _system »

The following users thanked this post: jeffreyH

• Jr. Member
• Posts: 15
##### Re: Does light wear out? And how far can it travel?
« Reply #5 on: 19/01/2016 04:48:52 »
Space has a groundstate. Light travels to the groundstate through interacting with light and impacts upon the groundstate. At the groundstate 4 types of particles are absorbed by the groundstate which maintains the construction and de-construction of the particles of the groundstate. The 4 absorbed particles are re-mitted by the groundstate and re-absorbed by the impacting light.

This specification is derived from the Paradigm of Types in Cosmology and Biology. A beginning to the application of the paradigm is presented in the essay “The Nature of the Universe and the Paradigm of Types in Cosmology and Biology”. The essay is located at home.spin.net.au/paradigm/true.pdf