Light (in fact everything) is a wave, with some traditional particle properties added in. It’s relatively easy to wrap your head around the weirdness from that point of view. It’s almost impossible to make sense of it from a “particle with wave properties” view.
It’s also worth noting that it is not observation, but measurement that matters. All observation is measurement but not all measurements are observations.
Basically, to measure something, you need to hit it with something else. Using a particle analogy (since the wave version is FAR less intuitive), imagine a pool ball, rolling down a table. You can only detect balls hitting the cushions. To measure where it is, in between, you need to roll additional balls across the table. In traditional physics, these balls can be thrown as lightly as you like, as accurately as you like. Unfortunately, the wave nature of the system imposes lower limits on this. When you throw a ball, it changes the ball it hits. To gain information, you end up damaging or destroying the system you are measuring.
In quantum mechanical terms, the wave function is collapsed. In fact, it’s combined with the new particles you used to measure things.
In the original post. When you’re not looking, the wave of the photon passes through both spits, it then interferes with itself. Only when it reaches the detector is it collapsed (by interacting with the atoms of the detector). When you try and measure which slit it went through, you introduce a new wave. This changes the shape of the original, and makes it appear like a particle.
It’s almost impossible to make sense of it from a “particle with wave properties” view.
“I want to emphasize that light comes in this form-particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you were probably told something about light behaving like waves. I’m telling you the way it does behave- like particles.”
Richard Feynman, “QED The Strange Theory of Light and Matter.” Introduction, Page 15.
As you read deeper, it’s more and more obvious. Light is neither. It’s a quantum mechanical object that has no direct analog in classical physics.
Under some conditions, the wave properties are dominant. In others, the particle. In most quantum mechanical problems, both are present.
My main point is that you get log jammed if you try and add the wave properties to a particle concept. There’s nothing it can properly connect to. However, a wave can look like a particle, if you set it up right, and squint hard enough. In graph form, it’s normal distribution with standard deviation close to zero. Basically a spike, with some slight rounding. It’s far from perfect, but it gives our limited brains an anchor to work from.
I would agree that light is neither but Feynman is very adamant that it’s a particle and he describes all the properties of light using a particle only model. It’s much simpler conceptually to keep everything as a particle than treating light as a wave that sometimes collapses to a particle.
In his book he used the Mayan numbering system as an analogy. You can do everything in math by counting one by one, it’s only extremely cumbersome. In a similar way he saw waves as a mathematical method to make calculating particles easier in some situations. But underlying the fancy math, it’s still counting one by one.
Feynman argues that you can calculate and observe everything as only particles but you can never observe waves and have to make waves instantly transform into particles if you treat them as waves.
Light (in fact everything) is a wave, with some traditional particle properties added in. It’s relatively easy to wrap your head around the weirdness from that point of view. It’s almost impossible to make sense of it from a “particle with wave properties” view.
It’s also worth noting that it is not observation, but measurement that matters. All observation is measurement but not all measurements are observations.
Basically, to measure something, you need to hit it with something else. Using a particle analogy (since the wave version is FAR less intuitive), imagine a pool ball, rolling down a table. You can only detect balls hitting the cushions. To measure where it is, in between, you need to roll additional balls across the table. In traditional physics, these balls can be thrown as lightly as you like, as accurately as you like. Unfortunately, the wave nature of the system imposes lower limits on this. When you throw a ball, it changes the ball it hits. To gain information, you end up damaging or destroying the system you are measuring.
In quantum mechanical terms, the wave function is collapsed. In fact, it’s combined with the new particles you used to measure things.
In the original post. When you’re not looking, the wave of the photon passes through both spits, it then interferes with itself. Only when it reaches the detector is it collapsed (by interacting with the atoms of the detector). When you try and measure which slit it went through, you introduce a new wave. This changes the shape of the original, and makes it appear like a particle.
This is quite a fun way of making yourself think in terms of waves. https://www.andreinc.net/2024/02/06/the-sinusoidal-tetris
I think this is the part I’ve always have had issue trying to understand, thanks for helping clarify with an example.
“I want to emphasize that light comes in this form-particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you were probably told something about light behaving like waves. I’m telling you the way it does behave- like particles.”
Richard Feynman, “QED The Strange Theory of Light and Matter.” Introduction, Page 15.
As you read deeper, it’s more and more obvious. Light is neither. It’s a quantum mechanical object that has no direct analog in classical physics.
Under some conditions, the wave properties are dominant. In others, the particle. In most quantum mechanical problems, both are present.
My main point is that you get log jammed if you try and add the wave properties to a particle concept. There’s nothing it can properly connect to. However, a wave can look like a particle, if you set it up right, and squint hard enough. In graph form, it’s normal distribution with standard deviation close to zero. Basically a spike, with some slight rounding. It’s far from perfect, but it gives our limited brains an anchor to work from.
I would agree that light is neither but Feynman is very adamant that it’s a particle and he describes all the properties of light using a particle only model. It’s much simpler conceptually to keep everything as a particle than treating light as a wave that sometimes collapses to a particle.
In his book he used the Mayan numbering system as an analogy. You can do everything in math by counting one by one, it’s only extremely cumbersome. In a similar way he saw waves as a mathematical method to make calculating particles easier in some situations. But underlying the fancy math, it’s still counting one by one.
Feynman argues that you can calculate and observe everything as only particles but you can never observe waves and have to make waves instantly transform into particles if you treat them as waves.