Aspects of quantum theory

[Quantum321]

Quantum theory is the theoretical basis of modern physics that explains the nature and behavior of matter and energy on the atomic and subatomic level. Lets discuss virtual photons and how they are exchanged by electrons. Virtual particles are an accepted particle in physics. Exactly what are virtual particles?

Edited December 14, 2016 by Quantum321

[Mordred]

Probably one of the simplist yet most accurate explanation can be found here.

 

https://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/

 

Essentially they are disturbances in a field or between two particles. Many refer to virtual particles being "off shell" of the real particle. Though this is accurate its still misleading in some sense.

 

Wiki alludes to this but the Profmattstrassler site does a far better job for laymen

Edited December 14, 2016 by Mordred

[Quantum321]

A virtual particle is a transient fluctuation that exhibits many of the characteristics of an ordinary particle, but that exists for a limited time.

Isn't this really saying ' something is going on we just don't understand?'

Edited December 14, 2016 by Quantum321

[StringJunky]

A virtual particle is a transient fluctuation that exhibits many of the characteristics of an ordinary particle, but that exists for a limited time.

Isn't this really saying ' something is going on we just don't understand?'

If they didn't know what was going on they wouldn't have given them a name.

[Quantum321]

I disagree. Physics gives names to countless things they don't understand like dark energy and dark matter.

[StringJunky]

I disagree. Physics gives names to countless things they don't understand like dark energy and dark matter.

That's why they are called 'dark'. They are placeholder names until they have some idea of their nature.

Edited December 14, 2016 by StringJunky

[Quantum321]

I just had one of my threads shut down by a monitor. Essentially it said a hypothesis was a guess. I just remembered one of Richard Feynmans quotes I loved. It was ""First you guess. Don't laugh, this is the most important step." I was just about to post it when the thread was closed. Pity.

[Strange]

A virtual particle is a transient fluctuation that exhibits many of the characteristics of an ordinary particle, but that exists for a limited time.

Isn't this really saying ' something is going on we just don't understand?'

Not really. It is saying that something is going on which is described by the mathematical theory and that can be considered analogous to "real" particles. (Have you read the page that Mordred linked?)

I just had one of my threads shut down by a monitor. Essentially it said a hypothesis was a guess. I just remembered one of Richard Feynmans quotes I loved. It was ""First you guess. Don't laugh, this is the most important step." I was just about to post it when the thread was closed. Pity.

The thing is, Feynman had a profound understanding of the subject he was "guessing" about. He wasn't just making stuff up.

 

Have you ever worked with real experts (in any subject)? They develop an ability to intuit what the right answer might be. But, even more importantly, the knowledge and skill to quickly recognise and reject incorrect guesses.

[StringJunky]

The thing is, Feynman had a profound understanding of the subject he was "guessing" about. He wasn't just making stuff up.

 

Have you ever worked with real experts (in any subject)? They develop an ability to intuit what the right answer might be. But, even more importantly, the knowledge and skill to quickly recognise and reject incorrect guesses.

"The more I practice, the luckier I get".

[Mordred]

Well proof is in the pudding. The majority of particle physics was predicted prior to measurement. Power of QM being extremely fundamental to making those predictions. Lets see 90% + percent of the particles we later discovered. Wavefunction characteristics of the quantum numbers. Higg's boson including the metastability relations.

 

The list goes on. The point being is the supposed lack of understanding doesn't follow the above. If we didn't have a good grasp we would not have been able to make those predictions.

 

The various formulas, symmetry relations, conservation laws (charge,lepton,spin,isospin,parity,momentum/energy,flavor,color)

These above conservation laws define what reactions can take place, how particles can decay, etc.

All the above isn't merely guess work but a consequence of understanding the key relations and interactions. Mostly via mathematical predictions.

 

So call it what you will based on your feelings and random guesswork rather than understanding and using the complicated math. Myself I will stick with the success story and the methodology that led to its success.

Edited December 14, 2016 by Mordred

[Quantum321]

My comments regarding hypothesis being guesses is in no way in no way contrary to everything you and strange have said. I consider the advancement of our world to be directly attributed to outstanding work of our scientists.

[Mordred]

No prob. One of the hardest aspects of QM is the need to stop thinking of particles as balls.

 

As the link explains they are essentially "excitations". Quantum numbers such as spin, charge, etc have wavefunctions.

 

Properties of a real particle are identical for every particle of the same type. They are identifiers in much the same way as a finger print. Those quantum numbers have a unique combined wavefunction. While in superposition this combined wavefunction is the probability function of all possible states. Once measurements occur you have determined which spin wavefunction etc is correct.

Thats your decoherence. At the same time the particle will also exhibit ball like (pointlike) characteristics. These pointlike qualities are more readily described in kinematic motion. (collisions etc,).

 

Now here is an important aspect of the Pauli exclusion principle with the above.

No two fermions can occupy the same space with identical combined quantum wavefunctions.

 

A virtual particle however may only have 1 or more of the same characteristics, however isn't required to have all of the same characteristics.(key note they can only exhibit characteristics of the real particle) In particular mean liftetime is shorter than that of the real particle.

 

It takes a bit to get a handle on the above. It does take a new way of viewing particles from the ball image.

 

PS Swansont may justifiably correct or restate the above. I am oversimplifying key aspects lol.

Edited December 15, 2016 by Mordred

[swansont]

A virtual particle is a transient fluctuation that exhibits many of the characteristics of an ordinary particle, but that exists for a limited time.

Isn't this really saying ' something is going on we just don't understand?'

Understanding isn't a binary state. As long as you treat it as such, there's no point in discussion.

[studiot]

Firstly you were told not to reopen this subject by a moderator,

 

But some good points have been made and the mods appear prepared to let this go on a least for a bit.

 

So I will make some observations.

 

 

Mordred mentions the difficulty reconciling the idea of multiple behaviours (eg particle and wave)

 

But in classical macro-mechanics this is no surprise.

 

The trouble is: IMHO too little classical stuff is taught today and too much black magic aspiration from the coalface of science.

 

 

Take particles.

 

Particles are an idealisation.

 

There is no such thing as the perfect particle from classical mechanics.

 

Consider the Earth, a tennis ball and a brace of jacks.

 

Are they particles? Indeed what are particles?

 

Well for the purposes of kinematics a particle is small enough that its dimensions are small compared to the system dimensions.

 

So for the purpose of solar orbital mechanics, the Earth is a particle.

 

But for the purpose of bouncing a tennis ball or playing jacks, Is the Earth still a particle?

 

And what off the ball and the jacks?

 

Does shape matter?

 

Certainly Earth gravity varies, depending on where you play ball or jacks.

 

But can the ball or jacks be considered particles?

 

Well what happens when you toss the ball onto a concrete path?

 

It bounces along and describes surprise surprise a wave?

 

It is only our imperfect world that prevent this wave continuing forever.

 

And the jacks. Do they act the same when tossed?

 

No the motion is quite different, perhaps you can continue the discussion?