Is Wavelength the Only Measure of Light's Size?

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In summary, the conversation discussed the concept of light having a size and occupying space, and whether measuring its wavelength actually measures the light itself. It was mentioned that according to quantum mechanics, a single photon does not have a well-defined size, but it can be localized when many photons are present. The question of whether the size of sound can also be measured by its wavelength was also brought up, with the response that wavelength is only one aspect of characterizing a wave and does not provide the full picture.
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swerdna
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Does light have a size? In other words, does it have dimensions and occupy space?

ETA - Is measuring the wavelength of light actually measuring light?
 
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Yes to all of the above.

Claude.
 
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Claude Bile said:
Yes to all of the above.

Claude.
Thanks - It’s hard to imaging being able to measure the size of something that has no mass and travels at around 300,000 kilometres per second! Can the size of sound also be measured by its wavelength?
 
  • #4
swerdna said:
Does light have a size? In other words, does it have dimensions and occupy space?

ETA - Is measuring the wavelength of light actually measuring light?

In terms of quantum mechanics, the position operator for modes of the electromagnetic field does not have an eigenvalue. In english, that means that the spatial localization of a single photon is not well-defined.

So, a single photon has no size. Technically, it has an infinite size- a single photon is everywhere becasue the momentum (wavelength) is precisely specified.

Obvously, there is spatial localization to light- we illuminate small parts of space all the time. But that's becasue we are using large numbers of photons and the momentum is no longer so well specified for the group.

As for measuring the wavelength 'actually' measuring light, that's kind of a philosophical question rather than a science question. We can reproducibly make a measurement of *something*- the angle of diffraction off a grating, energy by a photdetector, a frequency (or difference frequency), things that are tied to physical properties of light. Did you have a specific question about a specific result?
 
  • #5
swerdna said:
Can the size of sound also be measured by its wavelength?
Wavelength tells you the distance between successive peaks, it does not tell you anything about the spatial extent of the wave, the intensity of the wave, the direction it is moving in...

You can see where I'm getting at here, wavelength is one piece of the puzzle in terms of characterising a wave, but it is by no means the full story.

Claude.
 

1. Does light have a physical size?

Yes, light has a physical size, but it is extremely small. Light is made up of tiny particles called photons, which have a size of about 0.0000000000000000000000000000000001 meters. This is so small that it is often considered to be a point source and does not have a measurable size in everyday terms.

2. Is there a limit to how small light can be?

According to current scientific understanding, there is no limit to how small light can be. Photons are elementary particles, meaning they are not made up of smaller components. However, as the size of light particles approaches the Planck length (the smallest possible length in the universe), the laws of physics as we know them may break down.

3. Does the size of light affect its speed?

No, the size of light does not affect its speed. According to Einstein's theory of relativity, the speed of light is constant and does not change based on its size or any other factors. This means that a photon with a size of 0.0000000000000000000000000000000001 meters travels at the same speed as a larger photon, even though the larger photon would have more mass.

4. Can the size of light be measured?

Technically, yes, the size of light can be measured using specialized equipment such as electron microscopes. However, due to its incredibly small size, the measurement would be on a scale that is difficult for humans to comprehend and would require highly precise instruments.

5. Does the size of light affect its energy?

Yes, the size of light does affect its energy. The energy of a photon is directly proportional to its frequency, and the frequency is inversely proportional to its wavelength. Since smaller photons have a higher frequency and shorter wavelength, they have more energy than larger photons. This is why gamma rays (which have the smallest wavelengths) are more energetic than radio waves (which have the largest wavelengths).

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