# Do all light waves move at the same speed?

• hsdrop
In summary, the conversation discusses the nature of light, including its speed, oscillation, and shape. The concept of wave-particle duality is mentioned, as well as the idea of twisted light. The experts clarify that light does not physically move in a wave-like pattern and that its speed is constant in a vacuum. They also explain that the shape of a photon is not a meaningful concept and that it is simply an interaction between electromagnetic waves and matter. The conversation also touches on the speed of light in different mediums and the idea of a light beam propagating through space without interacting with matter.
hsdrop
I know photons all move at the speed of light and they move in a wave like pattern. So the question is. Do we take into account the up and down motion of the wave when we measure how fast it's moving or do we just measure the forward movement ?? For example, if the wave has higher and lower ups and downs would the wave cover more "ground" than a wave with lower ups and downs in the rate of speed forward? Please be kind with any response and if anyone is confused with what I'm asking I will try to draw out what I'm asking.
and a big thank you ahead of time to anyone that responds.

Light moves in a straight line. What has an oscillation is the electric and magnetic fields. When someone draws light like this

notice that only one of the axes represents space.

In vacuum, the speed on light is constant, whatever the frequency and amplitude of this oscillation.

hsdrop
I was under the idea that light traveled in a spiral, slinky, corkscrew like wave or at least that what I have been able to learn off the net so far...
so the photon travels strate and it gives off electric and magnetic fields with different frequency and amplitude of this oscillation.
am I getting the right idea maybe ??

hsdrop said:
I was under the idea that light traveled in a spiral, slinky, corkscrew like wave or at least that what I have been able to learn off the net so far...
That corkscrew picture probably corresponds to circular polarization of light. But there is nothing doing that motion in space.

hsdrop said:
so the photon travels strate and it gives off electric and magnetic fields with different frequency and amplitude of this oscillation.
am I getting the right idea maybe ??
It doesn't "give off" electric and magnetic fields, it has electric and magnetic fields. And you should not thing of light in terms of tiny particles called photons zipping about. You can see it has a wave of electromagnetic ration propagating in space.

Dale and hsdrop
ok maybe I should start out with does a photon have a shape?

hsdrop said:
ok maybe I should start out with does a photon have a shape?

This really depends on the photon's energy. All photons have the shape of the picture above. But all photons can also be treated as a particle (and higher energy photons are more particle-like). This is called wave-particle duality and you should read more about it.

hsdrop
hsdrop said:
ok maybe I should start out with does a photon have a shape?

Hercuflea said:
This really depends on the photon's energy. All photons have the shape of the picture above. But all photons can also be treated as a particle (and higher energy photons are more particle-like). This is called wave-particle duality and you should read more about it.

No, you cannot think of a photon as having a shape. It is not a particle in the sense that it is a little ball or some other shape. It is simply a quantized interaction between the EM wave and matter or another EM wave.

hsdrop and Dale
Hercuflea said:
This is called wave-particle duality and you should read more about it.

Wave-particle duality is an outdated concept and you shouldn't get that much into it. And what you wrote about shape of photon is completely not true. There is no meaningful way to talk about shape of elementary particles.

hsdrop
There have been a few articles recently about 'twisted light' - for example:
http://phys.org/news/2016-03-optical-slower.html
I am not sure whether the light here is actually following a curved path or if it is an interference pattern. This article implies that it is actually twisted so its straight line speed is marginally slower.

hsdrop
hsdrop said:
I know photons all move at the speed of light and they move in a wave like pattern. So the question is. Do we take into account the up and down motion of the wave when we measure how fast it's moving or do we just measure the forward movement ?? For example, if the wave has higher and lower ups and downs would the wave cover more "ground" than a wave with lower ups and downs in the rate of speed forward?

So the short answer is no because they don't physically "move in a wave like pattern".

I know photons all move at the speed of light

The speed of light is only a constant (c) in a vacuum. The speed of light in glass is about 2/3rds of the speed in a vacuum.

hsdrop
Even for waves that really do propagate in a wavelike pattern, you don't take into account the "up and down motion" when working with its speed.

hsdrop
Drakkith said:
No, you cannot think of a photon as having a shape. It is not a particle in the sense that it is a little ball or some other shape. It is simply a quantized interaction between the EM wave and matter or another EM wave.
What if the photon doesn't have anything to interact with and is just propagating through space? Would it not be like the picture in post 2?

Hercuflea said:
What if the photon doesn't have anything to interact with and is just propagating through space? Would it not be like the picture in post 2?
No. However, you've asked a very similar question in another thread: https://www.physicsforums.com/threa...er-interacts-with-matter.894667/#post-5628310
so we should continue the discussion there.

As the question that started this thread has been answered, we can close it.

hsdrop

## 1. Do all light waves have the same speed in a vacuum?

Yes, according to the theory of relativity, all light waves have the same speed in a vacuum, which is approximately 299,792,458 meters per second (or 186,282 miles per second).

## 2. Is the speed of light the maximum speed in the universe?

Yes, the speed of light is considered to be the maximum speed in the universe. This is because according to Einstein's theory of relativity, nothing can travel faster than the speed of light.

## 3. How does the speed of light compare to the speed of other waves?

The speed of light is significantly faster than the speed of other waves, such as sound waves or water waves. Light waves can travel through a vacuum, while other waves require a medium to travel through. Additionally, the speed of light is constant and does not change based on the wavelength or frequency of the light.

## 4. Can the speed of light be affected by gravity?

Yes, according to Einstein's theory of general relativity, gravity can affect the speed of light. This is because gravity can warp the fabric of space-time, causing light to travel along a curved path and appear to have a different speed.

## 5. Is the speed of light always the same in different mediums?

No, the speed of light can change when traveling through different mediums, such as air, water, or glass. This is because the density and composition of the medium can affect the speed of light. However, the speed of light is always constant in a vacuum.

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