Zero in physics

[pavelcherepan]

I was just thinking, can number zero describe a physical quantity of an object or is it more correct to say that the object doesn't possess that quality? For example, what is more correct: a) neutron has a zero electrical charge or b) neutron doesn't have electrical charge?

 

On one hand, since we can't quantify the value of it's charge, it doesn't have it. Period. On the other hand, neutron is the result of three quarks coming together and they do have charges and the sum of those is 0. In this case it would be rather strange that three entities that possess this quality will combine to form another entity that doesn't. I'm confused.

[fiveworlds]

Of course it can zero is arbitrary.

 

A better question would be how the combine. Do they merge into a single entity or are they three entities tied closely together. In one case the neutron is really neutral the other is a resultant of three unique waves and therefore not zero.

[Sensei]

You should start from learning how do we measure whether particle has charge or not.

It's done by passing particle in external electric field created by metal electrodes, one negatively charged, other one positively charged.

Negatively charged electrode has abundance of electrons, and positively charged has absence of electrons.

If we fire electron (electron gun) we will see that it is attracted to positively charged electrode.

If we will use positively charged particle, such as positron, pion+, muon+, kaon+, it'll be attracted by second negative electrode.

But if we would emit neutral particle (such as photon, neutrino, neutron, pion0, kaon0), its motion won't be altered by our external created electric fields..

 

Some unstable neutral particles, such as neutron, pion0, decays to positively and negatively charged particles.

So while doing our experiment in particle detector, its trace is starting appearing in middle of nowhere (without trace leading to place where it decayed).

Edited November 15, 2015 by Sensei

[ajb]

I would say that the neutron has zero charge, rather than no charge. I am not sure it makes much difference.

[studiot]

Well I think there is a difference and zero is not always arbitrary.

 

Pavel asked a wider question than his charge example so I will addres that.

 

Sometimes zero or not present make no (practical) difference.

 

But would you describe absolute zero of temperature as an arbitrary reference or zero being the same as the absence of temperature?

 

Some physical qwuantiies have continuous values that reduce to zero in certain circumstances, which may be very important.

 

For instance the resultant of a system of forces is always present and zero is neither arbitrary or equivalent to no forces being present at all.

 

I am rushing this because I see swansont hovering, maybe more later.

[Strange]

I was just thinking, can number zero describe a physical quantity of an object or is it more correct to say that the object doesn't possess that quality? For example, what is more correct: a) neutron has a zero electrical charge or b) neutron doesn't have electrical charge?

 

What is the difference?

 

On one hand, since we can't quantify the value of it's charge, it doesn't have it.

 

We can quantify it: zero.

[pavelcherepan]

I would say that the neutron has zero charge, rather than no charge. I am not sure it makes much difference.

 

It sort of does from my perspective. If we can measure something and find it infinitesimally small, but not zero we can still approximate it with a zero, but still it can be measured. On the other hand, if we can't measure something, can we describe it with a number?

 

 

But would you describe absolute zero of temperature as an arbitrary reference or zero being the same as the absence of temperature?

 

Some physical qwuantiies have continuous values that reduce to zero in certain circumstances, which may be very important.

 

For instance the resultant of a system of forces is always present and zero is neither arbitrary or equivalent to no forces being present at all.

 

I am rushing this because I see swansont hovering, maybe more later.

 

Thanks, studiot, these are good examples. As far as temperature and absolute zero is concerned I'd call it an abstraction, because even if it can be achieved, how do you measure an absolute zero temperature?

 

As for the example with forces, you can say that the object that forces are acting upon experiences no net force as if those didn't exist, yet the system as a whole can be described as having a number of forces that cancel each other.

 

Probably it's more of a philosophy forum question.

[Strange]

It sort of does from my perspective. If we can measure something and find it infinitesimally small, but not zero we can still approximate it with a zero, but still it can be measured. On the other hand, if we can't measure something, can we describe it with a number?

 

Why can't we measure zero?

[studiot]

 

As for the example with forces, you can say that the object that forces are acting upon experiences no net force as if those didn't exist, yet the system as a whole can be described as having a number of forces that cancel each other.

 

Hello pavel,

 

If you genuinely feel that zero resultant is the same as no force, try this experiment.

 

Go and stand in the middle of an empty horse park, where there are no forces acting on you (except gravity and the ground reaction).

 

Now obtain two equal on opposite horses, stretch out your arms and hitch a horse to each one and shout giddyup.

 

Do you still feel that they are the same?

 

[swansont]

 

Why can't we measure zero?

 

 

Sometimes you can, like if you are counting discrete objects under circumstances where you can be certain you can identify them all and not miss any. There are no elephants in my apartment, for example. (OK, hypothetically there none). Then you can measure zero with a sufficient level of confidence. But often enough you aren't in that situation. If you are trying to measure something that's supposed to be zero, like the mass of a photon, you won't be able to exclude values smaller than your experimental uncertainty with any confidence. Even for charge, we only measure zero under the assumption that it's quantized, because we have good reason to do so. But what if that assumption weren't valid? We pass a particle through an electric field and it deviates a small amount. There's only so much you can do to collimate the beam. Is missing the target by a small amount a limitation of that collimation or due to charge? That uncertainty (like others) can be made small, but it will never go to zero.

[Strange]

But is that different from measuring any other value? You can only measure the charge on the electron within certain error bounds and, as you say, we assume they all have exactly the same charge because it is quantised.

 

I guess I was really asking if measuring the charge of a photon or neutron as being zero is any different from measuring the charge of an electron or proton as being 1 (or -1)?

[studiot]

 

 

Sometimes you can, like if you are counting discrete objects under circumstances where you can be certain you can identify them all and not miss any. There are no elephants in my apartment, for example. (OK, hypothetically there none). Then you can measure zero with a sufficient level of confidence. But often enough you aren't in that situation. If you are trying to measure something that's supposed to be zero, like the mass of a photon, you won't be able to exclude values smaller than your experimental uncertainty with any confidence. Even for charge, we only measure zero under the assumption that it's quantized, because we have good reason to do so. But what if that assumption weren't valid? We pass a particle through an electric field and it deviates a small amount. There's only so much you can do to collimate the beam. Is missing the target by a small amount a limitation of that collimation or due to charge? That uncertainty (like others) can be made small, but it will never go to zero.

 

Do you not differentiate between the measurement situation for a continuous variable where values arbitrarily close to zero are permissible and variables where only certain values are permissible?

[swansont]

Do you not differentiate between the measurement situation for a continuous variable where values arbitrarily close to zero are permissible and variables where only certain values are permissible?

That's what I just discussed in the latter half of my post. Is there something I need to rephrase?

[ajb]

It sort of does from my perspective. If we can measure something and find it infinitesimally small, but not zero we can still approximate it with a zero, but still it can be measured.

That seems a question of experimental physics and especially experimental accuracy. The best one can usually do is say that the measurements are consistent with the theoretical understanding of 'X=0'.

 

For example, we have very good reasons to think that the photon is massless, i.e., the mass is zero. All experiments so far are consistent with this. However, no experiments will measure zero 'on the nose'. We have to do some data analysis and show that zero sits comfortably within this data.

 

On the other hand, if we can't measure something, can we describe it with a number?

If we cannot measure it, even in prinicial, then it cannot be an observable. However, it may still be mathematically modelled and an important concept in physics.

Edited November 16, 2015 by ajb