Electron And Positron

[swansont]

But you have used physical qualities in your example of how they can be different: size of 1 cm, different material.

 

Since point-like particles cannot be different in size, then are you saying that the electron and positron behave differently because they are made of different materials?

 

And you have moved the goalposts. You asked how they can have different properties but have the same shape. I have given you several examples. Physical properties need not emanate from the shape of an object.

 

This is quantum mechanics. Trying to describe fundamental particles with classical descriptions is going to fail — these are not little balls made of "stuff".

 

[Dekan]

 

 

This is quantum mechanics. Trying to describe fundamental particles with classical descriptions is going to fail — these are not little balls made of "stuff".

 

When you say "This is quantum mechanics"! Hasn't that got an awfully ominous ring? Like saying: "This isn't logic or reason - abandon them - it's QM"! Every real scientist suspects that QM is just another false theory. Like many other past theories, such as caloric fluid, phlogiston, and universal aether. These were sincerely believed in at the time, but have since been shown to be not true. And in due time, no doubt QM theory will go the same way. And 22nd Century Physicists will smile indulgently at QM, as they learn the true facts.

 

But in the meantime, we're forced to keep puzzling over QM's absurdities.

 

For example, if fundamental particles aren't made of "stuff", or "matter", what are they made of?

We see a material universe. Made of atoms, molecules, dust, asteroids, planets, nebulae, stars and galaxies. So - there must be some "stuff", to make all those physical structures?

Edited May 6, 2013 by Dekan

[Enthalpy]

You should have a thought at what means elementary particle. This is not even a matter of quantum mechanics.

[swansont]

When you say "This is quantum mechanics"! Hasn't that got an awfully ominous ring? Like saying: "This isn't logic or reason - abandon them - it's QM"!

 

I can see how it can sound ominous and be intimidating. The unknown often is. But QM does not require you to abandon logic or reasoning, just the preconceived notion of how things work that you have from watching macroscopic things. i.e. you have to abandon an incorrect premise.

 

Every real scientist suspects that QM is just another false theory.

 

And how do you think I should respond to such an insult? I don't suspect that QM is a false theory, in the category of caloric fluid, phlogiston, and universal aether.

 

 

Like many other past theories, such as caloric fluid, phlogiston, and universal aether. These were sincerely believed in at the time, but have since been shown to be not true. And in due time, no doubt QM theory will go the same way. And 22nd Century Physicists will smile indulgently at QM, as they learn the true facts.

 

By all means, conduct the experiments that show QM to be false. Until you do, though, this is just so much hot air.

 

Science is based on the best understanding we have at the time, which the way it was in the past. The models you mention were shown to flat-out contradict experiment, which is why they were abandoned. QM is better tested than any of them.

 

 

 

But in the meantime, we're forced to keep puzzling over QM's absurdities.

 

For example, if fundamental particles aren't made of "stuff", or "matter", what are they made of?

We see a material universe. Made of atoms, molecules, dust, asteroids, planets, nebulae, stars and galaxies. So - there must be some "stuff", to make all those physical structures?

 

That's an assumption you have — that there must be some "stuff" that makes up the particles. This is science — go test it. Don't make proclamations, especially when you have neither a model nor any experimental evidence that leads you to that position. Not "getting" how it can be so isn't evidence against the theory.

 

But your model has to agree with experiments already conducted. The evidence that we do have is that electrons are not composite particles and have no internal structure. The charge is not spread out over some volume.

[robinpike]

And you have moved the goalposts. You asked how they can have different properties but have the same shape. I have given you several examples. Physical properties need not emanate from the shape of an object.

 

This is quantum mechanics. Trying to describe fundamental particles with classical descriptions is going to fail — these are not little balls made of "stuff".

 

 

To be honest, I wish I could see the goal posts on this one! My question was whether we knew what the physical difference was between the electron and positron.

 

I am trying to understand the replies.

 

We have that the difference in behavior of the electron and positron, cannot be down to their shape, as they have no size, and therefore have no shape.

 

It is charge that makes the electron behave differently from the positron, and that charge is something that has no physical 'form', in the sense of shape or size.

 

So I guess the question has migrated to: how is the electric charge of the electron different to the electric charge of the positron?

 

To prevent further responses describing what the electron and positron do differently, or in what situations they behave differently, can we keep the replies to answering: How is the electric charge of the electron different to the electric charge of the positron?

 

Is it possible to answer this question without saying it is like 'this' or 'that', giving an example such as it is like two objects that have different colors, the example relying on the objects being different physically in shape and size (as in the atoms are different), and then saying, but charge is not like that because charge has no shape or size - and therefore making the explanation not appropriate?

[elfmotat]

Your new question is a bit like asking "how are 1 and 2 different numbers?"

[swansont]

So I guess the question has migrated to: how is the electric charge of the electron different to the electric charge of the positron?

 

To prevent further responses describing what the electron and positron do differently, or in what situations they behave differently, can we keep the replies to answering: How is the electric charge of the electron different to the electric charge of the positron?

 

Science involves investigating how things behave, not what they are. So describing how positive and negative charges behave is the only thing we can do. Charges don't "break open", i.e. that's not a behavior they perform, to let us look inside. So, in essence, you are asking the wrong question.

[Phi for All]

To prevent further responses describing what the electron and positron do differently, or in what situations they behave differently, can we keep the replies to answering: How is the electric charge of the electron different to the electric charge of the positron

 

!

Moderator Note

Let's also keep replies focused on mainstream explanations. This is not in the proper section to start questioning QM.

[michel123456]

1. A point like particle is described as such in 3D space. In spacetime it is supposed to be a line. So one could say that a point like particle is the section of a line at any instant in time.

If one cuts the section with a blade of zero width, in zero time, it should not be a surprise if one finds nothing.

 

2. A line could be a vector. That is a line with an arrow indicating direction. Since in this specific case the line is the result of Time it appears that the direction of the arrow is the direction of Time. And thus we get from observation a lot of electrons that are following naturally the arrow of time. From that point and after you have forbid to continue the conversation about reversing time.

 

3. IIRC there is a very interesting point raised by Brian Greene that compares the properties of an elementary particle to the properties of a Black Hole. Mind blowing. I'll have to dig a bit.

[ajb]

My question was whether we knew what the physical difference was between the electron and positron.

In light of quantum field theory, there is no difference in what the electron and positron are "made of". They are both understood as quanta of the same electron field; as already pointed out the electron and positron and mutual antiparticles. The difference of the two particles comes down to a few minus signs in the mathematics, you split the field up into positive and negative frequence parts and so on...

 

You can get an intuative picture of this using Feynman diagrams. "A positron is just an electron traveling backwards in time". In this way you see that the electron and positron have the same mass and spin, but opposite electric charge. I will say that this interpretaion is handwaving and comes from the mathematics, I am not really going to claim that electrons travel back in time, but this is loosley what the mathematics looks like.

[michel123456]

1. A point like particle is described as such in 3D space. In spacetime it is supposed to be a line. So one could say that a point like particle is the section of a line at any instant in time.

If one cuts the section with a blade of zero width, in zero time, it should not be a surprise if one finds nothing.

 

2. A line could be a vector. That is a line with an arrow indicating direction. Since in this specific case the line is the result of Time it appears that the direction of the arrow is the direction of Time. And thus we get from observation a lot of electrons that are following naturally the arrow of time. From that point and after you have forbid to continue the conversation about reversing time.

 

3. IIRC there is a very interesting point raised by Brian Greene that compares the properties of an elementary particle to the properties of a Black Hole. Mind blowing. I'll have to dig a bit.

Brian Greene's Elegant Universe in not free online.

 

Only some summary here.

 

"Chapter 13: Black Holes: A String/M-Theory Perspective

 

Greene makes an unlikely comparison between black holes

and elementary particles. Both, he says, have an internal structure

that physicists have yet to identify. It has recently been suggested

that an even greater similarity exists: perhaps black holes are

actually huge elementary particles. After all, Einstein set no minimum

limit on the mass of a black hole. Therefore, if we crushed a chunk

of matter into ever-smaller black holes, the result would be an

object no different from an elementary particle. This is because

both are defined by their mass, force charges, and spin."

[swansont]

String/M theory are not experimentally confirmed. Anyone offering it as evidence of anything has jumped the gun.

[robinpike]

 

I didn't say it wasn't a physical property, I said it wasn't a physical thing, i.e. something with a shape. Like color being a physical property, unaffected by shape.

http://en.wikipedia.org/wiki/Electric_charge

 

Hi Swansont,

 

In the above Wikipedia article, it defines electric charge as:

 

"Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter. There are two types of electric charges, called positive and negative."

 

And defines matter as:

 

"Matter, generally is a substance (often a particle) that has rest mass and (usually) also volume. The volume is determined by the three-dimensional space it occupies, while the mass is defined by the usual ways that mass is measured. Matter is also a general term for the substance that makes up all observable physical objects. ...

However, not all particles with rest mass have a classical volume, and fundamental particles such as quarks and leptons (sometimes equated with matter) are considered "point particles" with no effective size or volume. Nevertheless, quarks and leptons together make up "ordinary matter," and their interactions contribute to the effective volume of the composite particles that make up ordinary matter."

 

 

The Standard Model states that the electron and positron are elementary particles - that is the electron is not made of smaller parts.

 

So, whatever the electron is made of, it must be just one substance - because if it were to be made of several substances, then it would have parts to it - would you agree?

 

The Standard Model also states that the down quark is an elementary particle - that is the down quark is not made of smaller parts.

 

The electron has a -1 electric charge and the down quark has a -1/3 electric charge.

 

How is the down quark's electric charge able to be smaller than the electron's electric charge, if both particles are elementary?

 

Similarly, the electron has a mass of of 0.511 MeV (9.10938291 × 10-31 kilograms), whereas the down quark has a (bare) mass of 4.1–5.7 MeV/c2.

 

How is the down quark's (bare) mass able to be different to the electron's mass, if both particles are elementary?

[timo]

I think proper answers to your last two questions above are "quarks and electrons are different types of elementary particles". In fact, being confused about an elementary particle having less charge than an elementary electron seems to imply the thought of the particle containing an electron as part of it - which in turn seems to contradict the concept of a particle being elementary.

[ajb]

So, whatever the electron is made of, it must be just one substance - because if it were to be made of several substances, then it would have parts to it - would you agree?

My thought is that you are thinking too classically about all this. To understand fundamental particles the best models we have are based on quantum field theory. A rudimentary understanding of QFT may well help you.

How is the down quark's electric charge able to be smaller than the electron's electric charge, if both particles are elementary?

The fact that they are both elementary does not force them to have the same charge. So the question should be about the quantisation of charge and the fact that quarks have fractional charges. I am not able to give a clear explanation of this.

 

How is the down quark's (bare) mass able to be different to the electron's mass, if both particles are elementary?

Again, being fundamental does not force them to have the same properties.

 

In light of QFT, they are quanta of different fields and so we have no reason to expect them to have identical properies, at low energies anyway.

[swansont]

 

So, whatever the electron is made of, it must be just one substance - because if it were to be made of several substances, then it would have parts to it - would you agree?

No, and I think this is the underlying problem. I have said before, it's a mistake to think of the electron as made of "stuff". There's no substance. The electron is what it is.

[robinpike]

No, and I think this is the underlying problem. I have said before, it's a mistake to think of the electron as made of "stuff". There's no substance. The electron is what it is.

 

But what you are doing here is rather like this...

 

You and I are discussing what a tiger looks like. I produce a picture of an elephant and say this is what a tiger looks like.

 

You reply, no it doesn't, a tiger doesn't look anything like that picture.

 

So I ask, in that case what does a tiger look like...

 

You produce a blank piece of paper and add: this is an accurate picture of a tiger, since, as you can see, it has no discrepancies with what a tiger looks like!?

 

(I know... an electron has no size and shape, therefore a blank picture of an electron is correct!)

 

 

So back to the the electron and positron...

 

You argue that the electron is not made of "stuff", it is "what it is".

 

Fair enough, so I note: The electron is what it is, and the positron is what it is; and my referring to "what it is" as being "stuff" is incorrect, since "stuff" has shape and size, whereas "what it is" has no shape and no size.

 

 

I originally asked what is the physical difference between the electron and the positron.

 

The answer given was that they have opposite electric charge, with the proviso that it is incorrect to think of charge as having a physical shape (or "form" as I used).

 

So, have I got this correct...

 

The electron and positron are both made of "what it is" - cannot argue with that.

 

The "what it is" in the electron is different to the "what it is" in the positron?

[swansont]

"In the electron" is nonsensical in this context. There is no "in the electron". Re-phrasing the concept in different ways will not change the answer.

[Przemyslaw.Gruchala]

But what you are doing here is rather like this...

 

You and I are discussing what a tiger looks like. I produce a picture of an elephant and say this is what a tiger looks like.

 

You reply, no it doesn't, a tiger doesn't look anything like that picture.

 

So I ask, in that case what does a tiger look like...

 

You produce a blank piece of paper and add: this is an accurate picture of a tiger, since, as you can see, it has no discrepancies with what a tiger looks like!?

 

(I know... an electron has no size and shape, therefore a blank picture of an electron is correct!)

 

They believe in fields: one for photons, electrons, positrons, and yet another for quarks, and yet another for higgs...

 

So what do you expect from them?

It's not their own ideas, but what they learnt in schools from teachers.

They're just repeating it.

 

So back to the the electron and positron...

 

You argue that the electron is not made of "stuff", it is "what it is".

 

Fair enough, so I note: The electron is what it is, and the positron is what it is; and my referring to "what it is" as being "stuff" is incorrect, since "stuff" has shape and size, whereas "what it is" has no shape and no size.

 

From their point of view electron is wave on field with negative amplitude, and positron is wave on field with positive amplitude.

So from overlapping two such +wave and -wave there is nothing left (at least in that field).. Instead new waves are made in other fields..

 

 

 

 

 

In light of QFT, they are quanta of different fields and so we have no reason to expect them to have identical properies, at low energies anyway.

 

There is actually needed just one field for everything.

If you sit on decay table of the all particles and work it out with open mind..

And surprisingly you will have gravitation just like that for free.

Edited May 10, 2013 by Przemyslaw.Gruchala

[robinpike]

They believe in fields: one for photons, electrons, positrons, and yet another for quarks, and yet another for higgs...

 

From their point of view electron is wave on field with negative amplitude, and positron is wave on field with positive amplitude.

So from overlapping two such +wave and -wave there is nothing left (at least in that field).. Instead new waves are made in other fields..

 

That is interesting, for if an electron is a wave on a field and a positron is a wave on a field, then both have a shape, and it is meaningful to ask: What is the difference between the two shapes?

[Przemyslaw.Gruchala]

What is the difference between the two shapes?

 

Like they said - they don't model it using different shapes..

 

Just reversed sign.

 

If you have waves f.e. +sin(x) and -sin(x) and they overlap, result is +sin(x)-sin(x)=0..

 

http://en.wikipedia.org/wiki/Wave_function

[swansont]

Be advised that Przemyslaw is discussing his straw-man of physics, and not what is considered mainstream.

[ajb]

They believe in fields: one for photons, electrons, positrons, and yet another for quarks, and yet another for higgs...

 

 

From their point of view electron is wave on field with negative amplitude, and positron is wave on field with positive amplitude.

Frequency not amplitude, but okay. The electron and positron are exitations of the same field.

 

There is actually needed just one field for everything.

Maybe, but we do not know this for sure and we have not produced a mathematical description of this field. So, in the context of the standard model, we have a collection of different fields.

 

That is interesting, for if an electron is a wave on a field and a positron is a wave on a field, then both have a shape, and it is meaningful to ask: What is the difference between the two shapes?

 

Look at the plane wave expansion for the Dirac field here.

 

In scattering experiements plane waves for a basis of the fields involved. Or maybe more correctly, plave waves describe free states and these are the asymptotic states used in experiments. Note we have a whole load of mathematics here to study, consult Haag's book for details.

[timo]

Maybe, but we do not know this [if one needs only a single field for everything] for sure and we have not produced a mathematical description of this field. So, in the context of the standard model, we have a collection of different fields.

I don't think anything prevents you from labelling all like fields (e.g. all spinors) with integers, put them in a common tuple, call it a single field, and claim all elementary fermions being different excitations of the same field. And in that case, that also says quite a lot about the importance/relevance of void-of-content formal unification.

[ajb]

I don't think anything prevents you from labelling all like fields (e.g. all spinors) with integers, put them in a common tuple, call it a single field, and claim all elementary fermions being different excitations of the same field. And in that case, that also says quite a lot about the importance/relevance of void-of-content formal unification.

I also see no formal reason, but as you say it would contain no useful extra structure.