Looking at stars yesterday set me to thinking if there was such a thing as a maximum distance that light can travel…?
Clearly stars are less bright than our sun and this must be a function of their distance from us (and also their initial brightness). But these distances are absolutely, mind-bendingly huge: we can see stars thats are hundreds of millions of light years away. And they are still visible not only after huge distances but also massive amount of time.
So is light not subject to “decay” or some form of “resistance” to travel that would mean there is a limit to how far (length) or how long (time) it could travel before it becomes completely unseen?
I realise I am using analogies that would be more relevant to sound or waves in a liquid so it may just be my incomprehension of the “light” phenomena and how it works that means ive missed the point… 😀
In: Physics
The short answer is yes: up to about 15 billion light years.
A quick explanation of why this happens:
You’ve probably heard of ‘redshift’ before when describing distance galaxies. Basically, as light travels, it gradually loses energy. Light is a form of electromagnetic radiation, and one of its properties is ‘wavelength’, or the distance between the crests and troughs of its frequency.
As light loses energy, it goes from a short wavelength to a longer wavelength. As it does, it moves deeper into the red portion of the visible light spectrum (which has the longest wavelength of all electromagnetic energy that we can perceive with our eyes, as opposed to blue light which has the shortest wavelength). Eventually, the wavelength gets too long to be in the visible light spectrum at all, becoming infrared radiation.
Another term you’ve probably heard before is the ‘cosmic microwave background’, or CMB. This was once the light of the big bang, but over billions of years it’s shifted even lower in the electromagnetic spectrum, going from infrared to microwave radiation. Eventually, it will become radio waves, which have the longest wavelength of all electromagnetic energy. And then it will disperse completely within the local electromagnetic perturbations of a cold, dark universe.
Latest Answers