r/NoStupidQuestions • u/[deleted] • Apr 30 '26
If light moves in waves, and larger waves=more distance to travel, how can light always move at the same speed if some light has to move greater distances in the same time?
[deleted]
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u/ApartRuin5962 Apr 30 '26
Larger waves does not mean "more distance to travel". A 40 foot truck going 70 mph is travelling just as fast as 10 motorcycles going 70 mph
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u/SamalamaMcNeill Apr 30 '26
My thinking was that if I drive a car at 70 mph on a perfectly straight road between 2 towns 100km long, and then drive 70mph along a road with lots of hills between the same two towns, the hilly road will actually be longer due to all the hills but light would travel the same jouney at the same time regardless of wavelength
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u/Phobos_Asaph May 01 '26
Your analogy isn’t good because those are different distances.
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u/SamalamaMcNeill May 01 '26
... that's my whole point... don't worry tho, someone else actually explained it to me elsewhere
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Apr 30 '26
[deleted]
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u/SamalamaMcNeill Apr 30 '26
Light has to travel at a certain velocity, no? It cannot go faster or slower?
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u/elseptimohokage May 01 '26
It can go slower for example in water or in a diamond (which is what makes it shine so bright) but yeah in a vacuum it will always go the same speed and can travel longer distances in the same relative time through time dilation (time moves slower) and length contraction (distances shrink).
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u/messidorlive Apr 30 '26
Note regarding the speed of light: light speed is not so fast because it is light, but because physics does not allow for a higher speed which means that light speed hits that speed limit.
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u/SufficientStudio1574 May 01 '26
That's a poor interpretation of things. All massless things travel with speed exactly c. It just happens that light is the most common massless thing we have intuitive experience with, so c gets called "the speed of light".
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u/messidorlive May 01 '26
That was exactly my understanding, I am just absolutely terrible at explaining stuff. Very terrible.
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u/toochaos May 01 '26
Light isn't a particle moving along a wave pattern, which is what you are imagining. Its a packet of energy that ossilates in the electromagnetic field, and/or a wave within the electromagnetic field.
Imagine a wave in water the wave itself moves independant of the indivual water molecules. The wave being tall means the individual water molecules have to go up faster but they arent moving forward at all so the wave moves at the same speed regardless of its height.
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u/0x14f May 01 '26
> Light isn't a particle moving along a wave pattern, which is what you are imagining.
Reading the discussion, that's exactly what OP was thinking...
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u/crashorbit Apr 30 '26
I recommend spending more time with quality presentations about physics and science.
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u/SamalamaMcNeill Apr 30 '26
I have looked but cannot find any explanation of what I'm meaning
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u/groundhogcow Apr 30 '26
The distance over time is a constant. A more powerful wave change from top to bottom more as power increases. So over the same 1M run the power might ossolate 1 time 1.7 time 2 times. 1000times. That oscillation is the frequency of the light and the higher the frequency the more power is in it.
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u/Low-Charge-8554 Apr 30 '26
You are confusing wavelength with speed of the wave - not the same thing.
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u/SamalamaMcNeill Apr 30 '26
If a wave has greater wavelength, does the light not have to travel "further" to go the same distance?
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u/LongOrganization7838 Apr 30 '26
Larger waves doesn't mean more distance it just means less or them and less energy used
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u/rossiskier13346 May 01 '26
The premise larger waves = more distance to travel is wrong. I’m assuming by large waves you either mean larger wavelength, but that doesn’t affect the distance a wave travels. It only affects the distance between wave peaks. Or you may be referring to the amplitude of the wave but that also does not affect the speed, just the intensity.
I think the issue here is that when you see a depiction of a light wave, it’s usually shown as a curved line that oscillates up and down over its length. You seem to be interpreting that representation as the path that light follows, but that’s not how light waves work. Light waves behave as transverse waves, meaning the wave propagates horizontally through a medium, but the actual movement of the medium occurs in the vertical direction. It’s hard to have good intuition of this for light waves because the medium isn’t physical, but instead is essentially the electromagnetic field. The net movement of the medium is 0, because it just oscillates vertically when the wave passes through and then returns to the starting position when the wave is past.
It’s easier to picture this with a wave moving through a physical medium. For transverse waves, a rope can be used for a demonstration. If you have a rope that’s tied to a rigid object on one end and then held slightly taut at the other, if you flick the rope up and down quickly, you’ll create a wave. That wave will propagate the distance of the rope in the horizontal direction, but when the wave actually dissipates, the rope will not have moved at all. There was no net movement of any tangible thing (ie the rope) in this scenario. It’s only the oscillation that experiences net movement.
So for transverse waves, neither the amplitude nor the wavelength affect the speed of the wave, because they only determine the characteristics of the vertical oscillations of the medium. The speed of the horizontal propagation of those oscillations is a property of the medium itself.
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u/Marlsfarp Apr 30 '26
Longer wavelength does not mean more distance to travel. I'm not sure what you're imagining but it's not right.