Parth G | Do Antiparticles Move BACKWARDS in Time? @ParthGChannel | Uploaded 2 years ago | Updated 7 hours ago
Antimatter is just like normal matter - except all antiparticles have the opposite charge to matter particles. But why do some physicists think of antiparticles as travelling backwards in time?
In this video, we will be looking at two particle interaction processes that commonly occur in our universe. Then, we will see what links these two processes, despite initially looking quite different. Finally, we'll learn a very basic (but not very rigorous) way to understand the notion that antiparticles move backwards in time.
The first process we will study is Compton Scattering. This occurs when a photon interacts with an electron. A photon carries some amount of energy, related to the wavelength of the source of EM waves from which it was created. The larger the wavelength, the less energy it carries. It's worth noting though that all photons travel through space at the same speed - the speed of light.
So when a photon meets an electron, the photon can transfer some energy to the electron so that it starts moving through space. As a result, the original photon is said to be "absorbed" by the electron, and a new photon is released. This new photon has energy equal to the original photon's energy minus the energy given to the electron. This way conservation of energy is obeyed. But also, conservation of momentum is obeyed too! The two new particles (new photon and electron) move through space so that the original photon momentum matches the electron and new photon's momenta.
The second process looks at the interaction between an electron and its antiparticle, the positron. All particle that have the same values for all possible descriptors, e.g. mass, charge, spin, etc., are said to be the same type of particle. All electrons have the same mass, charge, etc. But if we take a particle and we now consider another one with all the same descriptors except the opposite sign of charge, then we are looking at the original particle's antiparticle. In other words, the positron has all the same properties as the electron except it is positively charged rather than negative.
When a particle and its antiparticle meet, they annihilate each other and two photons are released. These two photons combined have the same amount of energy as the initial two particles had. This process is known as pair annihilation. And aside from involving similar particles to Compton Scattering, it seems to be quite different to Compton Scattering.
However, if we use "Crossing Symmetry", we see that these two processes are not so different. When we write any of these processes in equation form, we can take any of the particles on either side (the reactant/before side or the product/after side) and move it to the other side of the equation, provided we turn it into its antiparticle. This is explained in more detail in the video.
If we start with pair annihilation and move the positron to the other side, while doing the same with one of the photons (using Crossing Symmetry of course), we end up with Compton Scattering! These processes are said to be inherently the same "process".
But more importantly, Crossing Symmetry allows us to consider the idea that a particle on the "after" side of any equation would turn into its antiparticle on the "before" side. Since an equation showing particle interactions allows us to see how particles behave over time, we can therefore imagine that the antiparticle is moving backwards in time relative to the original particle. This is one of the very basic explanations of why antiparticles can be though of as moving backwards in time compared to their particles.
In reality though, the mathematics of particle physics makes it difficult to differentiate between a particle moving forward in time, and its antiparticle moving backward in time. That's the true reason for this notion - though it doesn't mean antiparticles do actually move backward in time! It's just a cool thing to think about.
Thanks for watching, please do check out my socials here:
Instagram - @parthvlogs
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Quantum Physics Book I Enjoy: https://amzn.to/3sxLlgL
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Timestamps:
0:00 - Particle Physics - Two Processes That Are Surprisingly Similar
0:50 - Process 1: Compton Scattering
2:30 - Antiparticles: The Very Basics
3:56 - Process 2: Pair Annihilation
4:26 - Crossing Symmetry
6:15 - Do Antiparticles Move Backwards In Time? A Visual Analogy
Antimatter is just like normal matter - except all antiparticles have the opposite charge to matter particles. But why do some physicists think of antiparticles as travelling backwards in time?
In this video, we will be looking at two particle interaction processes that commonly occur in our universe. Then, we will see what links these two processes, despite initially looking quite different. Finally, we'll learn a very basic (but not very rigorous) way to understand the notion that antiparticles move backwards in time.
The first process we will study is Compton Scattering. This occurs when a photon interacts with an electron. A photon carries some amount of energy, related to the wavelength of the source of EM waves from which it was created. The larger the wavelength, the less energy it carries. It's worth noting though that all photons travel through space at the same speed - the speed of light.
So when a photon meets an electron, the photon can transfer some energy to the electron so that it starts moving through space. As a result, the original photon is said to be "absorbed" by the electron, and a new photon is released. This new photon has energy equal to the original photon's energy minus the energy given to the electron. This way conservation of energy is obeyed. But also, conservation of momentum is obeyed too! The two new particles (new photon and electron) move through space so that the original photon momentum matches the electron and new photon's momenta.
The second process looks at the interaction between an electron and its antiparticle, the positron. All particle that have the same values for all possible descriptors, e.g. mass, charge, spin, etc., are said to be the same type of particle. All electrons have the same mass, charge, etc. But if we take a particle and we now consider another one with all the same descriptors except the opposite sign of charge, then we are looking at the original particle's antiparticle. In other words, the positron has all the same properties as the electron except it is positively charged rather than negative.
When a particle and its antiparticle meet, they annihilate each other and two photons are released. These two photons combined have the same amount of energy as the initial two particles had. This process is known as pair annihilation. And aside from involving similar particles to Compton Scattering, it seems to be quite different to Compton Scattering.
However, if we use "Crossing Symmetry", we see that these two processes are not so different. When we write any of these processes in equation form, we can take any of the particles on either side (the reactant/before side or the product/after side) and move it to the other side of the equation, provided we turn it into its antiparticle. This is explained in more detail in the video.
If we start with pair annihilation and move the positron to the other side, while doing the same with one of the photons (using Crossing Symmetry of course), we end up with Compton Scattering! These processes are said to be inherently the same "process".
But more importantly, Crossing Symmetry allows us to consider the idea that a particle on the "after" side of any equation would turn into its antiparticle on the "before" side. Since an equation showing particle interactions allows us to see how particles behave over time, we can therefore imagine that the antiparticle is moving backwards in time relative to the original particle. This is one of the very basic explanations of why antiparticles can be though of as moving backwards in time compared to their particles.
In reality though, the mathematics of particle physics makes it difficult to differentiate between a particle moving forward in time, and its antiparticle moving backward in time. That's the true reason for this notion - though it doesn't mean antiparticles do actually move backward in time! It's just a cool thing to think about.
Thanks for watching, please do check out my socials here:
Instagram - @parthvlogs
Patreon - patreon.com/parthg
Music Chanel - Parth G's Shenanigans
Merch - https://parth-gs-merch-stand.creator-spring.com/
Here are some affiliate links for things I use! I make a small commission if you make a purchase through these links.
Quantum Physics Book I Enjoy: https://amzn.to/3sxLlgL
My Camera: https://amzn.to/2SjZzWq
ND Filter: https://amzn.to/3qoGwHk
Microphone (Fifine): https://amzn.to/2OwyWvt
Gorillapod: https://amzn.to/3wQ0L2Q
Timestamps:
0:00 - Particle Physics - Two Processes That Are Surprisingly Similar
0:50 - Process 1: Compton Scattering
2:30 - Antiparticles: The Very Basics
3:56 - Process 2: Pair Annihilation
4:26 - Crossing Symmetry
6:15 - Do Antiparticles Move Backwards In Time? A Visual Analogy
