Can matter be completely converted to energy as suggested by E=mc2?

[thefifthlord]

Well the only assumption i really made was that rest mass referred to a particle that was absolutely still. If this particle were to be vibrating, or doing any sort of movement, i'd understand.

Assuming p = h/lambda seems pretty correct to me unless someone wants to suggest otherwise?

 

[DaveC426913]

Well the only assumption i made was that rest mass referred to a particle that was absolutely still. If this particle were to be vibrating, or doing any sort of movement, i'd understand.

Precisely.

 

[thefifthlord]

So its just called rest mass for the heck of it?

I mean honestly, I've been ranting on here for hours... Why in the world would they call something at rest when its still moving in some way.

 

[atyy]

What I'm trying to understand is how

with the Equation E^2 = m^2c^4 + p^2c^4

assuming p = h/lambda

A particle at rest (by rest i assume there is absolutely no movement of any kind vibration or otherwise) doesn't have an infinite amount of energy when the wavelength of the particle can be said to be 0. I mean there is absolutely no way to differentiate between an absolutely still object, and an absolutely vibrating object that has a 0 amplitude(due to the wavelength being 0).

There's no such thing as infinite energy (well, or if there is, our theories break down quite a bit before that).

Going with finite energy, almost zero momentum is almost infinite wavelength which is almost a flat line, while very high momentum is short wavelength which is a rapid vibration, those are very different. An absolutely vibrating object with zero amplitude is an object that doesn't exist, since, roughly speaking, the amplitude of a quantum mechanical wave determines the probability of its existence.

 

[DaveC426913]

So its just called rest mass for the heck of it?

I mean honestly, I've been ranting on here for hours... Why in the world would they call something at rest when its still moving in some way.

Did you read atyy's https://www.physicsforums.com/showpost.php?p=2536550&postcount=28"?

 

[atyy]

So its just called rest mass for the heck of it?

Quantum mechanically, I'd say that's a good way to start thinking about it (ie. quantum mechanically it's just something in the dispersion relation of a wave). The name really makes sense only classically. Remember that even "particle" and "movement" don't have the same meaning in quantum mechanics as in classical mechanics. Particles do not move in trajectories with definite momentum and position at all times.

 

[thefifthlord]

Well then I'm sorry for dragging this along. I was too sure of my logic to check my assumptions.

Thanks for the replies.

BTW, this should be stickied so no more like these are made, i was aware of similar topics but none of them addressed all the issues.

 

[jtbell]

So its just called rest mass for the heck of it?

I mean honestly, I've been ranting on here for hours... Why in the world would they call something at rest when its still moving in some way.

This is why many physicists (myself included) prefer to use the term invariant mass, which can be calculated via mc^2 = \sqrt {E^2 - (pc)^2}, which gives the same result for any particular particle in any inertial reference frame. This avoids the incongruity of talking about "rest mass" of a particle that is never at rest.

I consider the term "rest mass" to be a historical anachronism which will unfortunately probably never die because of its widespread use in pop-sci books and even many introductory textbooks.

 

[diazona]

You're talking quantum mechanically, right? Because if even an isolated classical particle can't be at rest in some reference frame, something is seriously wrong with my understanding...

BTW, this should be stickied so no more like these are made, i was aware of similar topics but none of them addressed all the issues.

The same could be said of half the threads here. Of course, I'm not the one to make such a decision, but it's awfully presumptuous to assume that your particular misunderstanding needs to be brought to everybody's attention.

 

[Dale]

So its just called rest mass for the heck of it?

The polite term is for "historical reasons". But yes, that is essentially correct.

 

[Frame Dragger]

The polite term is for "historical reasons". But yes, that is essentially correct.

I think these terms of art trip people up more than teachers and professionals realize. I know that terms such as "colour and spin" often are chosen for some vague reason (three primary colours for isntance) in QM. "Rest Mass" really is incredibly misleading, and as another user Zenith said in another thread, "Perception shapes thinking." I know that it's difficult to use language to communicate mathematical concepts, but if we expect people to look at theoretical physics/SR/GR/QM the way they grasp concepts such as "radio" and chain reaction there has to be more effort to universally formalize the language.

For god's sake, this is the hardest (as in hard/soft) science there is and one of the primary subatomic particles is named from Finnegan's Wake! "Three quarks for muster mark...". BIOLOGY has clearer nomenclature, and yes, I mean that as an insult to us all. The language must keep pace with the times... anachronisms that misleading are nothing for the community to be proud of.

 

[atyy]

I think these terms of art trip people up more than teachers and professionals realize. I know that terms such as "colour and spin" often are chosen for some vague reason (three primary colours for isntance) in QM. "Rest Mass" really is incredibly misleading, and as another user Zenith said in another thread, "Perception shapes thinking." I know that it's difficult to use language to communicate mathematical concepts, but if we expect people to look at theoretical physics/SR/GR/QM the way they grasp concepts such as "radio" and chain reaction there has to be more effort to universally formalize the language.

For god's sake, this is the hardest (as in hard/soft) science there is and one of the primary subatomic particles is named from Finnegan's Wake! "Three quarks for muster mark...". BIOLOGY has clearer nomenclature, and yes, I mean that as an insult to us all. The language must keep pace with the times... anachronisms that misleading are nothing for the community to be proud of.

So, why is an action potential a depolarization?

 

[Frame Dragger]

So, why is an action potential a depolarization?

That's incredibly simple. Without depolarization at the axon hillock there would be no voltage and therefore the firing threshold of the neuron would never be met and the neuron wouldn't be able to carry out the electrical portion of its electrochemical communication. Why do you ask?

EDIT: Did you ask me this because you think I'm slandering Biology? I'm sorry if I offended, but in the hierarchy of sciences physics is by its very nature the most fundamental. A complete understanding of physics could allow a complete understanding of all other sciences. No other science is so fundamental. That doesn't make them unworthy pursuits, or "easy", it just is a fact of life that each science is derived in sequence: Physics, Chemistry, Organic Chemistry/Biology. They logically lead to each other, although that is certainly not how they were constructed in real life. Please don't mistake an observation and a bit of rhetorical flair for a real stab at a branch of scientific research.

 

[Naty1]

If so then how do we define rest mass seeing as everything's moving?

Absolute zero doesn't mean "no motion".

An increasingly confined particle will become incredibly active in accordance with the Heisenberg uncertainty principle...as it's wavelength is constrained it's frequency increases...

Zero point energy is the minimum energy of a system...check it out for a start at http://en.wikipedia.org/wiki/Zero-point_energy

 

[Altabeh]

From above:
"

I don't think that is accurate; in any case QED has been experimentally verified to exquisite detail, roughly 1 part in 10¹²...and special relativity is pretty secure so far that photons ARE massless...

Yeah... no one criticized the experimental aspect of QED and if the theory itself gets shaky by assuming a massive photon, then nothing can change the observed results. So your post is pointless. We were just taking about the loss of gauge invariance in QED which would be there if we assumed photons are massive.

AB

 

[atyy]

That's incredibly simple. Without depolarization at the axon hillock there would be no voltage and therefore the firing threshold of the neuron would never be met and the neuron wouldn't be able to carry out the electrical portion of its electrochemical communication. Why do you ask?

But a depolarization does mean zero voltage (potential difference). So if there is a depolarization, then there is zero voltage. An action potential is a voltage - (50 mV potential difference between the inside and outside of the cell), not a depolarization.

EDIT: Did you ask me this because you think I'm slandering Biology? I'm sorry if I offended, but in the hierarchy of sciences physics is by its very nature the most fundamental. A complete understanding of physics could allow a complete understanding of all other sciences. No other science is so fundamental. That doesn't make them unworthy pursuits, or "easy", it just is a fact of life that each science is derived in sequence: Physics, Chemistry, Organic Chemistry/Biology. They logically lead to each other, although that is certainly not how they were constructed in real life. Please don't mistake an observation and a bit of rhetorical flair for a real stab at a branch of scientific research.

Nah, I thought you're "slandering physics"

 

[Naty1]

Why in the world would they call something at rest when its still moving in some way.

It's all relative, pun intended.

Many terms in common use today have historical origins...physics included...their adoped intepretation on is regularly superseded at a later date by new discoveries or theories that make them somewhat obsolete. It's analogous to asking why left and right have the orientation we all recognize.

 

[Frame Dragger]

But a depolarization does mean zero voltage (potential difference). So if there is a depolarization, then there is zero voltage. An action potential is a voltage - (50 mV potential difference between the inside and outside of the cell), not a depolarization.



Nah, I thought you're "slandering physics"

When depolarization occurs there are ion pumps in the cell which allow for the voltage to occur, and then flood the cell to bring it back into equilibrium. I should add that depolarization in biology is almost a completely different term than it is in physics. Frankly, other than amusing yourself I'm unclear on the purpose of this inquiry.

 

[Dale]

I think these terms of art trip people up more than teachers and professionals realize.

I agree, but I don't know a solution. The historical terms and concepts are in all of the historical documents which are still in use today. Unfortunately, we can't edit the past in order to clear things up. In the end I think it is required that each person learn the terminology with all of its many vagaries and flaws and understand that it is essentially what you would expect as the result of such a very poorly organized committee.

I would love to be able to issue an executive decree banning the term "relativistic mass" in favor of "total energy" and replacing the term "rest mass" with the term "invariant mass" and one more decree requiring any unqualified use of the term "mass" to refer to the invariant mass.

 

[Frame Dragger]

I agree, but I don't know a solution. The historical terms and concepts are in all of the historical documents which are still in use today. Unfortunately, we can't edit the past in order to clear things up. In the end I think it is required that each person learn the terminology with all of its many vagaries and flaws and understand that it is essentially what you would expect as the result of such a very poorly organized committee.

I would love to be able to issue an executive decree banning the term "relativistic mass" in favor of "total energy" and replacing the term "rest mass" with the term "invariant mass" and one more decree requiring any unqualified use of the term "mass" to refer to the invariant mass.

Agreed on all fronts, but since we (the USA) couldn't even make the switch to metric as a society, I'm guessing that reconciling this language may take a longer period of time than the theories will remain as they are now. Sort of like recession speed increasing past c :)

 

[DaveC426913]

I think these terms of art trip people up more than teachers and professionals realize.

I agree, but I don't know a solution.

I disagree. The solution is to pay attention. The sciences are not a place to go if you're looking or neat packaged ideas that fit into your preconceptions.

A student needs to know what an ampere is to understand how to use it. Or a litmus test. Or a particle at rest.

A student will run into lots of trouble if he hears a word or phrase and starts demanding that he knows what it means, despite people telling him it is not as he expects.

 

[Frame Dragger]

I disagree. The solution is to pay attention. The sciences are not a place to go if you're looking or neat packaged ideas that fit into your preconceptions.

A student needs to know what an ampere is to understand how to use it. Or a litmus test. Or a particle at rest.

A student will run into lots of trouble if he hears a word or phrase and starts demanding that he knows what it means, despite people telling him it is not as he expects.

This is a somewhat hermetic view of science. Everyone who needs to understand concepts in physics to enrich their lives doesn't need these pointless hurdles in their way. Yes, people should pay attention as that is the only practical solution to the problem, however that isn't ideal and it is a pointless waste of energy.

If we're looking to discard preconceptions than using terms such as colour and spin and rest-state, etc... are not going to help people. The concept of colour and rotation and rest are fundamental for all people before physics can EVER enter the equation. That means all people must learn and keep track of these multiple definitions.

It's possible, it's not overly taxing, but it's a pointless and wasteful exercise that COULD be corrected.

 

[DaveC426913]

Everyone who needs to understand concepts in physics to enrich their lives doesn't need these pointless hurdles in their way.

This is the same rationale that led to one US state petitioning to redefine pi as 3.

Let's get rid of hurdles involved in students actually learning the science. Let's put science on laminated placards in large letters to make it easier for them to pass the year.

 

[Frame Dragger]

This is the same rationale that led to one US state petitioning to redefine pi as 3.

Let's get rid of hurdles involved in students actually learning the science. Let's put science on laminated placards in large letters to make it easier for them to pass the year.

There is a VAST difference between codifying language that is archaic, and simplifying the fundamental science for the sake of people who have no business in that field. You're too smart not to know that... having some rhetorical fun are we?

 

[atyy]

Would anyone go so far as to say with 't Hooft "But there is another pedagogical point. I see no reason to shield students against the phenomenon of changes of convention and notation. Such transitions are necessary whenever one switches from one field of research to another. They better get used to it."?

 

[Frame Dragger]

Does this in any way add to the science, or the process of sharing information across multiple disciplnes? If so, I'm aching to hear the ways it does. It's an admirably Calvinist attitude, but in terms of learning and information sharing it is indefensible... which is probably why when I keep making points about efficiency, the riposte is off that topic entirey. Hence, this is the pride and ignorance of academia you so often find in the best people. Ah well.

 

[atyy]

Well, if you object to "colour" because it existed in plain English first, then recall that "mass" was used in Newtonian theory first.

 

[Frame Dragger]

Well, if you object to "colour" because it existed in plain English first, then recall that "mass" was used in Newtonian theory first.

I object to colour because while it's easy to understand both the reasoning and the results, it is a needless use of a fundamental concept. Let's be honest, science tends to let these things be named by their discoverers, or collective whimsy. Again... "Three quarks for muster mark." Cute, but not really useful. Shouldn't scientific language evolve with the times instead of becoming a linguistic ruin?

EDIT: Also, the fact that it existed in "plain english" isn't the issue. The fact that we as a species are sight-primary when it comes to senses, and colour is not just a preconcieved linguistic notion, but a VERY basic one. That may explain the modern etymology, but it doesn't excuse it.

 

[HallsofIvy]

This is the same rationale that led to one US state petitioning to redefine pi as 3.

I feel I have to jump into rebut this calumny! (The state was Indiana, by the way.) Specifically, what happened was that House Bill No 246, Indiana Legislature, 1897 began "A bill for an act introducing a new mathematical truth and offered as a contribution to education to be used only by the state of Indiana free of cost by paying any royalties whatever on the same, provided it is accepted by the official action of the legislature of 1997". Of course, you can't charge royalties for the use of "a new mathematical truth' or any truth! But a legislator offered this bill on behalf of a constitutent and, since it didn't actually commit the state to doing anything, most legislators didn't bother to look at it very closely. The paper included trisection of an angle, duplicating the cube, and squaring the circle! It also noted that his quadrature of the circle has been "published in the American Mathematical Monthly, where it was, in fact, run as an advertisement. It also claimed that the work had been approved by specificly named people at the National Astronomical Observatory, University of Michigan, and Johns Hopkins- all of whom later denied even knowing the person who wrote it. The paper doesn't give a value for pi, although as many as nine different values can be deduced from his various calculations.

This is from Underwood Dudley's book "Mathematical Cranks" where he also gives references to "The legal values of \pi", published in the Mathematical Intelligencer, volume 7 (1985) pages 69- 72, and "Indiana's squared circle" buy Arthur Hallerberg, in the Mathematics Magazine, volume 50 (1977), pages 136 to 140.

Let's get rid of hurdles involved in students actually learning the science. Let's put science on laminated placards in large letters to make it easier for them to pass the year.

 

[DaveC426913]

I feel I have to jump into rebut this calumny! (The state was Indiana, by the way.) Specifically, what happened was that House Bill No 246, Indiana Legislature, 1897 began "A bill for an act introducing a new mathematical truth and offered as a contribution to education to be used only by the state of Indiana free of cost by paying any royalties whatever on the same, provided it is accepted by the official action of the legislature of 1997". Of course, you can't charge royalties for the use of "a new mathematical truth' or any truth! But a legislator offered this bill on behalf of a constitutent and, since it didn't actually commit the state to doing anything, most legislators didn't bother to look at it very closely. The paper included trisection of an angle, duplicating the cube, and squaring the circle! It also noted that his quadrature of the circle has been "published in the American Mathematical Monthly, where it was, in fact, run as an advertisement. It also claimed that the work had been approved by specificly named people at the National Astronomical Observatory, University of Michigan, and Johns Hopkins- all of whom later denied even knowing the person who wrote it. The paper doesn't give a value for pi, although as many as nine different values can be deduced from his various calculations.

This is from Underwood Dudley's book "Mathematical Cranks" where he also gives references to "The legal values of \pi", published in the Mathematical Intelligencer, volume 7 (1985) pages 69- 72, and "Indiana's squared circle" buy Arthur Hallerberg, in the Mathematics Magazine, volume 50 (1977), pages 136 to 140.

Um, can you paraphrase? What is the upshot?