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Author Topic: Do scientists know what mass is?  (Read 6798 times)

Offline MichaelS

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Do scientists know what mass is?
« on: 02/10/2009 16:05:41 »
Do scientists understand what mass is?



 

Offline JP

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Do scientists know what mass is?
« Reply #1 on: 02/10/2009 16:22:48 »
We understand how it works on different scales, but we don't know what it "is."  Most modern physicists would claim that knowing what something "is" isn't possible--all we can do is describe how things behave within the limits of our theories.  If someone comes up with an ultimate "theory of everything" that can never be improved upon, then maybe we could claim to know what things actually are.

In the case of mass, we know how it behaves on large scales (using general relativity) and how it behaves no small scales (in quantum mechanics), but we don't know how to join the two theories, or what gives rise to mass on small scales--you just have to choose arbitrary numbers for mass, you can't yet predict mass from some underlying theory.
 

Offline MichaelS

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Do scientists know what mass is?
« Reply #2 on: 02/10/2009 17:44:18 »
We understand how it works on different scales, but we don't know what it "is."  Most modern physicists would claim that knowing what something "is" isn't possible--all we can do is describe how things behave within the limits of our theories. 

ack. sounds like a justification for their own lack of understanding to me. Just because "they" don't know what something is, doesn't mean it can't be known.

some particles are "massless" correct. Photons are one. are there others?

also, are photons fundamental. that is, are they made up of smaller quarks and leptons.

and what's the difference between a quark and a lepton?

sorry for all the questions. I find this stuff fascinating but confusing at the same time

m

 

Offline lightarrow

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Do scientists know what mass is?
« Reply #3 on: 02/10/2009 18:19:17 »
I think it is correct to say "mass is..." or anyother concept in physics, as long as this concept has been *defined*. For example: velocity IS the time derivative of space. At the end, however, you obviously reach a point where you cannot define the terms anylonger, and this is true even in a language...

So the answer to the OP's question is: mass is...as it's defined in the different situations, and if you take the more general case that we know, that is general relativity, those situations are in a great number.
See:
http://en.wikipedia.org/wiki/Mass_in_general_relativity

If you only need to know what is mass in special relativity, this is the definition:

mass is the modulus of the 4-momentum, divided by c. In formulas:
 
m = (1/c2)Sqrt[E2 - (cp)2]

where E = energy; p = momentum.
« Last Edit: 02/10/2009 18:25:42 by lightarrow »
 

Offline JP

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Do scientists know what mass is?
« Reply #4 on: 02/10/2009 19:47:41 »
Good point, lightarrow.  Context is everything.
 

Offline LeeE

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Do scientists know what mass is?
« Reply #5 on: 02/10/2009 19:48:54 »
I think JP's answer hits the nail on the head here.

What he alludes to by saying "Most modern physicists would claim that knowing what something "is" isn't possible" is that you can only say what something is in terms of something else, which then begs the question "what is the something else that we've use to define the original something?  That's why the question is fundamentally unanswerable in absolute terms.

It's an inevitable consequence of the analytic process that the only final answer you can arrive at is an abstract that cannot be defined in further depth, otherwise it's not the final answer.
 

Offline MichaelS

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Do scientists know what mass is?
« Reply #6 on: 02/10/2009 19:53:16 »
m = (1/c2)Sqrt[E2 - (cp)2]

where E = energy; p = momentum.

ok so to me this doesn't look like a definition, it looks like an estimation (and a complicated one at that). Would that be correct to say?

« Last Edit: 02/10/2009 19:56:11 by MichaelS »
 

Offline MichaelS

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Do scientists know what mass is?
« Reply #7 on: 02/10/2009 19:57:43 »

What he alludes to by saying "Most modern physicists would claim that knowing what something "is" isn't possible" is that you can only say what something is in terms of something else, which then begs the question "what is the something else that we've use to define the original something?  That's why the question is fundamentally unanswerable in absolute terms.

That's only if you believe that you can't reduce everything to a single, fundamental something. So would it be fair to say that that is an assumption of modern physics?

m
 

Offline JP

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Do scientists know what mass is?
« Reply #8 on: 02/10/2009 19:58:09 »
ack. sounds like a justification for their own lack of understanding to me. Just because "they" don't know what something is, doesn't mean it can't be known.
Modern physics assumes that the ultimate test of everything is what we can observe.  If two explanations give identically observable results, there's no way to pick which one is "right."  (There are a lot of different philosophical interpretations of what quantum mechanics means, for example.)  If you have a theory that describes mass well enough for all the experiments you want to do, would you say that that theory tells you what mass is?  

As Bill Clinton famously said, "It depends on what the meaning of the word 'is' is."  

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some particles are "massless" correct. Photons are one. are there others?
Gluons are expected to be massless.  Neutrinos might have no mass, but recent evidence suggests they have a very tiny mass.

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also, are photons fundamental. that is, are they made up of smaller quarks and leptons.
Photons are fundamental.  The fundamental particles are the quarks, leptons and bosons, which are summarized in this nice table of the Standard Model.
http://en.wikipedia.org/wiki/File:Standard_Model_of_Elementary_Particles.svg

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and what's the difference between a quark and a lepton?

Quarks can interact via the strong force, while leptons can't.  There's other differences, but that's the big one.
 

Offline MichaelS

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Do scientists know what mass is?
« Reply #9 on: 02/10/2009 20:07:38 »
ack. sounds like a justification for their own lack of understanding to me. Just because "they" don't know what something is, doesn't mean it can't be known.
Quote
Modern physics assumes that the ultimate test of everything is what we can observe.  If two explanations give identically observable results, there's no way to pick which one is "right."  (There are a lot of different philosophical interpretations of what quantum mechanics means, for example.)  If you have a theory that describes mass well enough for all the experiments you want to do, would you say that that theory tells you what mass is?  


Excellent point. Technically no. based on the epistemological criteria of observability, then unless you've observed something directly, you an never know what it is. But mass is something that can be observed by it's measurement. That is, you know something has mass because it's difficult to move. So mass is equivalent to inertia? Or mass is a measure of how difficult it is to get something moving, or to stop it. How much force is required? Hmm. Maybe a better question is what causes mass?


Quote
Quarks can interact via the strong force, while leptons can't.  There's other differences, but that's the big one.

Which practically means that quarks (plural) form neutrons and protons, and leptons don't. So an electronic is a lepton and is so because "inside" it is a single particle?

The electromagnetic force is what brings the protons and neutrons together right?

m

p.s. thanks for the table ref. that was very helpful!

m
 

Offline syhprum

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Do scientists know what mass is?
« Reply #10 on: 02/10/2009 21:19:38 »
The mass of hadrons far exceeds the mass of the consistent quarks in as much as their mass can be measured, the balance is assumed to be made up by the binding energy of the gluon's.
 

Offline JP

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Do scientists know what mass is?
« Reply #11 on: 02/10/2009 22:47:21 »
Maybe a better question is what causes mass?
That's what I assumed you were asking in the original post, which is something that there is no satisfactory answer to yet. 

Quote
Which practically means that quarks (plural) form neutrons and protons, and leptons don't. So an electronic is a lepton and is so because "inside" it is a single particle?

The electromagnetic force is what brings the protons and neutrons together right?
Electrons are leptons because of how their properties, but basically it comes down to them being fundamental particles, with no smaller "bits" inside of them.  Protons and neutrons are hadrons, which are made up of smaller particles, called quarks.  That table listed all the fundamental particles we know of. 

It's the residual strong force left over from the quarks inside of the protons and neutrons that holds the protons and neutrons together in atomic nuclei. Electromagnetism is the force that holds the negatively charged electrons in place around the positively charged nucleus.
 

Offline Vern

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Do scientists know what mass is?
« Reply #12 on: 02/10/2009 23:37:38 »
Quote from: MichaelS
Do scientists understand what mass is?

Some of us do.

What is mass? Mass is electromagnetic change. There is no instance where a change in electric and magnetic amplitude can not be observed as mass. So in that sense, a photon has no mass because a photon is mass.

We might get a clue in the equation that relates mass to electromagnetic change. It seems I remember it as m = hv / c2. The only variable in that equation is electromagnetic change. So why not take it at face value. If we choose the units to take out the constants all we have left is m = v. v is nothing more than a change in electromagnetic amplitude.
« Last Edit: 02/10/2009 23:43:46 by Vern »
 

Offline MichaelS

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Do scientists know what mass is?
« Reply #13 on: 02/10/2009 23:58:48 »
So why not take it at face value. If we choose the units to take out the constants all we have left is m = v. v is nothing more than a change in electromagnetic amplitude.

ok, but then what is electromagnetic amplitude? And I though Electromagnetism operated only at the level of electrons and atomic nuclei?

m
 

Offline Mr. Scientist

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Do scientists know what mass is?
« Reply #14 on: 03/10/2009 01:38:45 »
Do scientists understand what mass is?



Sure we do.

We know that for instance, in relative terms that energy is a diffused form of matter under the famous conversion of E=Mc^2. Energy is very devoid of a total structure on macroscopic events. It's a highly unstable fluctuation of the quantum vacuum, one in all relative terms, seems to have a long life. Energy forms into matter so matter is but a more stable form of energy, that is, until its portion is finally reduced back to energy through a matter-antimatter collision. The proces is normally accepted among scientists as a type of quantum decay.

Matter is not ethereal like energy. Matter has a substance. Matter when in the billions of billions of particles, gather together with a great deal more structure an balance to it. The fact we can touch solid matter is usually associated to this; however matter is only tangible to our senses of touch, not because the said object is made of matter, but because the structure of the object is made from electrons, which act on external bodies like little magnets repelling each other. This is what keeps my body from having the floor dissipate from my feets grip, and fall towards the center of the earth. 
 

Offline Vern

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« Reply #15 on: 03/10/2009 12:28:21 »
Quote from: MichaelS
ok, but then what is electromagnetic amplitude? And I though Electromagnetism operated only at the level of electrons and atomic nuclei?
Electromagnetic amplitude is the gauge of strength of electric and magnetic events in space. Electromagnetism operates at all levels and diminishes in value as the square of distance from a radiating source. The radiating source is always two equal points of electromagnetic saturation that are opposite in charge.  These points move through space at their natural speed of light. We call them photons.
 

Offline Vern

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Do scientists know what mass is?
« Reply #16 on: 03/10/2009 13:26:08 »
Quote from: Mr. Scientist
Matter is not ethereal like energy.
We can think of energy that way, but consider this: All of the movement of matter is the result of the exchange of energy.

We like to think of energy as a property of a thing and not a thing itself. This might not be the most useful view of energy. All things might simply be the energy they contain. If you take away all the energy from any physical thing, you find that you no longer have a physical thing.
 

Offline Mr. Scientist

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Do scientists know what mass is?
« Reply #17 on: 03/10/2009 17:25:51 »
Quote from: Mr. Scientist
Matter is not ethereal like energy.
We can think of energy that way, but consider this: All of the movement of matter is the result of the exchange of energy.

We like to think of energy as a property of a thing and not a thing itself. This might not be the most useful view of energy. All things might simply be the energy they contain. If you take away all the energy from any physical thing, you find that you no longer have a physical thing.

Well, energy is certainly the system in play. Matter is just another form of energy. And does not matter require to use its internal kintic energy to move?
 

Offline Vern

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Do scientists know what mass is?
« Reply #18 on: 03/10/2009 18:06:18 »
I think that it is only a change in motion that requires the use of energy. Acceleration might be a better term. Acceleration requires energy; steady state motion does not; of course we all know that.
 

Offline LeeE

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Do scientists know what mass is?
« Reply #19 on: 03/10/2009 20:44:56 »

What he alludes to by saying "Most modern physicists would claim that knowing what something "is" isn't possible" is that you can only say what something is in terms of something else, which then begs the question "what is the something else that we've use to define the original something?  That's why the question is fundamentally unanswerable in absolute terms.

That's only if you believe that you can't reduce everything to a single, fundamental something. So would it be fair to say that that is an assumption of modern physics?

m

It doesn't make any difference how many fundamentals you end up with; even if you can reconcile everything to a single fundamental you'll still only be able to describe it in terms of itself, at which point it becomes abstract.  I wouldn't say that it's an assumption of physics but is instead a logical truth.
 

Offline yor_on

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Do scientists know what mass is?
« Reply #20 on: 03/10/2009 20:44:56 »
I liked jpetruccelli's first definition. We are inside spacetime looking at it. To us mass 'is' and depending on what we deem this 'is' to be we will have our definition. To a goldfish view the 'distortion of sight' we know it to observe as it looks out the bowl into our living room is the 'truth'. And mathematically it is a truth as it will be a correct observation from it's point of view only needing some corrective definitions from our view to 'fit'. The problem is to know where those partial 'truths' ends. The question when narrowed down is the one of 'objectivity'. Is there a 'objective truth' explaining everything?

And that to me becomes a philosophical problem. Is there one 'truth' describing them all, or will there only be 'partial truths' that mixed together presents us with spacetime? String theory tries to build from a 'objective' 'whole' truth, if I get it right, with the addendum that I believe it to presume there to be one-dimensional strings already existing? Then we have other definitions too, like 'dimension less points' which seems almost mystical :)to their nature. The question might be if we see SpaceTime as something with a 'boundary' limiting it and if we then expect it to be something outside that 'boundary' defining it. Or, if we like I believe is only 'emerging' as restricted phenomena of a greater 'whole' in where we don't really exist. If that would be the case then SpaceTime will be our 'balloon' and the idea of inside/outside will lose its relevance. And then those 'dimension less points' are the reality.

We will narrow it down further, on that I'm sure. But if that will lead to us to a 'greater perspective' I don't know. We are very much 'goldfishes' too. Defining our world from what we can observe. But that is the way we have to go it seems to me. So MichaelS if you have another idea how we should make our observations feel free to present it/them. We've gone some way since we thought that it was the Gods deciding what our world should be, and we still have some way to go :)

« Last Edit: 03/10/2009 20:47:14 by yor_on »
 

Offline LeeE

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Do scientists know what mass is?
« Reply #21 on: 03/10/2009 20:47:18 »
Ooo - wow! a simultaneous posting!

It confused me when I saw yor_on's post after I sent my one  ???
 

Offline yor_on

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Do scientists know what mass is?
« Reply #22 on: 03/10/2009 21:05:19 »
Yep, a 'Jungian' experience LeeE :)
'Synchronity' in action.
 

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