# Observations takne at the speed of light

I've heard the concept of an observer traveling at the speed of light, but when i placed myself in that observer's shoes i came to wonder; If someone was actually traveling at the speed of light, would/could they SEE anything at all? wouldn't the wavelength of the light be outside of the spectrum of visible light?

Dale
Mentor
2020 Award
It is not possible for any object with mass to travel at the speed of light.

Yeah, as DaleSpam said, an object with mass cannot travel at the speed of light. However, if one were able to travel at c, then the only light that would reach the observer's eyes would be the light directly in front of his or her eyes.

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DaveC426913
Gold Member
Yeah, and the only light that will reach the observers eyes is the light directly in front of his or her eyes.
No. There is no 'and'. Dalespam's post has a full stop at the end.

DaveC426913
Gold Member
I've heard the concept of an observer traveling at the speed of light, but when i placed myself in that observer's shoes i came to wonder; If someone was actually traveling at the speed of light, would/could they SEE anything at all? wouldn't the wavelength of the light be outside of the spectrum of visible light?
While one cannot travel at the speed of light, can can get arbitrarily close to it.

As you approach relativistic velocities, the light coming at you from the front will get be more and more blueshifted. Indeed, visible light will be blueshifted way up the spectrum, into UV, X-ray and gamma ray frequencies. This is one of the big showstoppers for relativistic travel - it will bring with it lethal levels of very hard radiation.

Note BTW that, as far as what the observer can see: infra-visible light will be blue-shifted into the visible spectrum. So what was originally infra-red, microwaves and radio waves will now become visible.

No. There is no 'and'. Dalespam's post has a full stop at the end.

Excuse me. I've been texting too much with people who don't care much for things like that. As a result, I've gotten into some bad habits. :/ Thank you for pointing that out to me. I will be more careful in the future. I will fix it immediately.

the question I asked wasn't very specific, what i am really wondering about is when we travel very very quickly, not at the speed of light, but very fast away from a light source, wouldn't the wavelength of the light coming from the light source become so long that it is outside of the spectrum of visible light?

ZapperZ
Staff Emeritus
the question I asked wasn't very specific, what i am really wondering about is when we travel very very quickly, not at the speed of light, but very fast away from a light source, wouldn't the wavelength of the light coming from the light source become so long that it is outside of the spectrum of visible light?

There's nothing special about "visible light". That's why we have radio astronomy, IR detection, etc. Just because it is outside of the visible light spectrum, it doesn't mean we can't detect it. We've been doing that already for a very long time.

Zz.

DaveC426913
Gold Member
the question I asked wasn't very specific, what i am really wondering about is when we travel very very quickly, not at the speed of light, but very fast away from a light source, wouldn't the wavelength of the light coming from the light source become so long that it is outside of the spectrum of visible light?
Yes. If you looked out the rear of your spacecraft, the light would appear more and more redshifted, down through microwave and radio frequencies.

Note though, that there is always UV light, X-rays and gamma rays impinging on you, which will be progressively redshifted down into the visible spectrum as you go faster.

So, you will still be able to "see", just things will look more and more weird.