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[Off-topic] Requests author discusses MentalHealthError exception

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  [Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-02-27 20:37 +1100
    Re: [Off-topic] Requests author discusses MentalHealthError exception Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-02-27 09:50 +0000
    Re: [Off-topic] Requests author discusses MentalHealthError exception Ethan Furman <ethan@stoneleaf.us> - 2016-02-27 14:06 -0800
    Re: [Off-topic] Requests author discusses MentalHealthError exception Jason Friedman <jsf80238@gmail.com> - 2016-02-27 17:00 -0700
    Re: [Off-topic] Requests author discusses MentalHealthError exception Larry Martell <larry.martell@gmail.com> - 2016-02-29 11:21 -0500
    Re: [Off-topic] Requests author discusses MentalHealthError exception Ian Kelly <ian.g.kelly@gmail.com> - 2016-02-29 09:47 -0700
    Re: [Off-topic] Requests author discusses MentalHealthError exception Ben Finney <ben+python@benfinney.id.au> - 2016-03-01 03:56 +1100
      Re: [Off-topic] Requests author discusses MentalHealthError exception Rustom Mody <rustompmody@gmail.com> - 2016-02-29 09:08 -0800
        Re: [Off-topic] Requests author discusses MentalHealthError exception Ben Finney <ben+python@benfinney.id.au> - 2016-03-01 04:33 +1100
          Re: [Off-topic] Requests author discusses MentalHealthError exception Rustom Mody <rustompmody@gmail.com> - 2016-02-29 09:54 -0800
        Re: [Off-topic] Requests author discusses MentalHealthError exception Larry Martell <larry.martell@gmail.com> - 2016-02-29 17:40 -0500
        Re: [Off-topic] Requests author discusses MentalHealthError exception Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-02-29 23:29 +0000
        Re: [Off-topic] Requests author discusses MentalHealthError exception Joel Goldstick <joel.goldstick@gmail.com> - 2016-02-29 18:33 -0500
        Re: [Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-03-02 04:05 +1100
          Re: [Off-topic] Requests author discusses MentalHealthError exception Rustom Mody <rustompmody@gmail.com> - 2016-03-02 09:02 -0800
            Re: [Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-03-03 13:27 +1100
              Re: [Off-topic] Requests author discusses MentalHealthError exception Chris Angelico <rosuav@gmail.com> - 2016-03-03 13:35 +1100
                Re: [Off-topic] Requests author discusses MentalHealthError exception alister <alister.ware@ntlworld.com> - 2016-03-03 17:21 +0000
                  Re: [Off-topic] Requests author discusses MentalHealthError exception Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-03 11:03 -0700
                    Re: [Off-topic] Requests author discusses MentalHealthError exception alister <alister.ware@ntlworld.com> - 2016-03-03 20:20 +0000
                      Re: [Off-topic] Requests author discusses MentalHealthError exception Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-03 13:33 -0700
                      Re: [Off-topic] Requests author discusses MentalHealthError exception William Ray Wing <wrw@mac.com> - 2016-03-03 18:02 -0500
                        Re: [Off-topic] Requests author discusses MentalHealthError exception alister <alister.ware@ntlworld.com> - 2016-03-04 14:05 +0000
                      [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Steven D'Aprano <steve@pearwood.info> - 2016-03-04 11:04 +1100
                        Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-03-04 10:19 +0000
                          Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Marko Rauhamaa <marko@pacujo.net> - 2016-03-04 12:38 +0200
                            Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Dan Sommers <dan@tombstonezero.net> - 2016-03-04 13:10 +0000
                            Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-03-04 17:35 +0000
                              Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] André Roberge <andre.roberge@gmail.com> - 2016-03-04 11:12 -0800
                              Re: [Still off-top] Physics [was Requests author discusses   MentalHealthError exception] Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-03-05 15:51 +1300
                                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Chris Angelico <rosuav@gmail.com> - 2016-03-05 14:13 +1100
                                  Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Marko Rauhamaa <marko@pacujo.net> - 2016-03-05 10:31 +0200
                                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2016-03-05 13:11 +0000
                                  Photon mass (was: [Still off-top] Physics) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-05 16:38 +0100
                                Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception] Gene Heskett <gheskett@wdtv.com> - 2016-03-05 10:15 -0500
                                  Photon mass (was: [Still off-top] Physics) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-05 16:46 +0100
                                    Re: Photon mass (was: [Still off-top] Physics) Gene Heskett <gheskett@wdtv.com> - 2016-03-05 12:36 -0500
                                    Re: Photon mass (was: [Still off-top] Physics) Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-03-06 12:16 -0500
                                    Re: Photon mass (was: [Still off-top] Physics) Larry Martell <larry.martell@gmail.com> - 2016-03-06 09:21 -0500
                          Re: [Still off-topic] Physics Steven D'Aprano <steve@pearwood.info> - 2016-03-06 16:36 +1100
                      Re: [Off-topic] Requests author discusses MentalHealthError   exception Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-03-04 19:34 +1300
                        Re: [Off-topic] Requests author discusses MentalHealthError   exception Marko Rauhamaa <marko@pacujo.net> - 2016-03-04 08:52 +0200
              Re: [Off-topic] Requests author discusses MentalHealthError exception Rustom Mody <rustompmody@gmail.com> - 2016-03-02 19:57 -0800
                Re: [Off-topic] Requests author discusses MentalHealthError exception Ian Kelly <ian.g.kelly@gmail.com> - 2016-03-02 23:44 -0700
                Re: [Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-03-04 02:50 +1100
                Re: [Off-topic] Requests author discusses MentalHealthError exception Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-03 16:21 +0000
        Re: [Off-topic] Requests author discusses MentalHealthError exception Anders Wegge Keller <wegge@wegge.dk> - 2016-03-03 08:23 +0100
      Re: [Off-topic] Requests author discusses MentalHealthError exception Paul Rubin <no.email@nospam.invalid> - 2016-02-29 16:35 -0800
        Re: [Off-topic] Requests author discusses MentalHealthError exception Ethan Furman <ethan@stoneleaf.us> - 2016-02-29 16:54 -0800
    Re: [Off-topic] Requests author discusses MentalHealthError exception Larry Martell <larry.martell@gmail.com> - 2016-02-29 17:36 -0500
    Re: [Off-topic] Requests author discusses MentalHealthError exception Larry Martell <larry.martell@gmail.com> - 2016-02-29 17:38 -0500
      Re: [Off-topic] Requests author discusses MentalHealthError exception Steven D'Aprano <steve@pearwood.info> - 2016-03-01 23:13 +1100
        Re: [Off-topic] Requests author discusses MentalHealthError exception "Sven R. Kunze" <srkunze@mail.de> - 2016-03-01 17:49 +0100
    Re: [Off-topic] Requests author discusses MentalHealthError exception "Mario R. Osorio" <nimbiotics@gmail.com> - 2016-02-29 20:11 -0800
    Re: Photon mass (was: [Still off-top] Physics) Gene Heskett <gheskett@wdtv.com> - 2016-03-06 16:46 -0500
    Re: Photon mass (was: [Still off-top] Physics) Larry Martell <larry.martell@gmail.com> - 2016-03-06 17:51 -0500

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#103988

On Thu, Mar 3, 2016 at 1:20 PM, alister <alister.ware@ntlworld.com> wrote:
> On Thu, 03 Mar 2016 11:03:55 -0700, Ian Kelly wrote:
>
>> On Thu, Mar 3, 2016 at 10:21 AM, alister <alister.ware@ntlworld.com>
>> wrote:
>>> On Thu, 03 Mar 2016 13:35:12 +1100, Chris Angelico wrote:
>>>> 1) No physical object can have negative mass.
>>>> 2) I am a part of the universe and have positive mass.
>>>> 3) I am not Kenneth.
>>>> 4) The sum of my mass and Kenneth's mass must exceed Kenneth's mass
>>>> alone.
>>>>
>>>> Unless someone wants to dispute 1 or 2, we can be logically certain.
>>>>
>>>> ChrisA
>>>
>>> Anti Matter?
>>
>> Antimatter has positive mass.
>
> Are you sure?
>  mix 1 atom of hydrogen + 1 of anti hydrogen & you end up with 0 mass (+
> LOTTS of energy)
>
> To be honest it is all over my head

Ah, I thought you were challenging 1) or 2), not 4). Anyway, we can
sum the mass of matter and antimatter without annihilating them.

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#104004

> On Mar 3, 2016, at 3:20 PM, alister <alister.ware@ntlworld.com> wrote:
> 
> On Thu, 03 Mar 2016 11:03:55 -0700, Ian Kelly wrote:
> 
>> On Thu, Mar 3, 2016 at 10:21 AM, alister <alister.ware@ntlworld.com>
>> wrote:
>>> On Thu, 03 Mar 2016 13:35:12 +1100, Chris Angelico wrote:
>>>> 1) No physical object can have negative mass.
>>>> 2) I am a part of the universe and have positive mass.
>>>> 3) I am not Kenneth.
>>>> 4) The sum of my mass and Kenneth's mass must exceed Kenneth's mass
>>>> alone.
>>>> 
>>>> Unless someone wants to dispute 1 or 2, we can be logically certain.
>>>> 
>>>> ChrisA
>>> 
>>> Anti Matter?
>> 
>> Antimatter has positive mass.
> 
> Are you sure?

The ALPHA experiment at CERN is attempting a direct measurement of the mass of anti-hydrogen by trapping atoms of the stuff in a penning trap at high vacuum. The answer isn’t definitive yet as the error bars are huge and extend past zero, but are centered on the positive side.

-Bill


> mix 1 atom of hydrogen + 1 of anti hydrogen & you end up with 0 mass (+ 
> LOTTS of energy)
> 
> To be honest it is all over my head
> 
> 
> 
> -- 
> I used to be Snow White, but I drifted.
> 		-- Mae West
> -- 
> https://mail.python.org/mailman/listinfo/python-list

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#104039

On Thu, 03 Mar 2016 18:02:04 -0500, William Ray Wing wrote:

>> On Mar 3, 2016, at 3:20 PM, alister <alister.ware@ntlworld.com> wrote:
>> 
>> On Thu, 03 Mar 2016 11:03:55 -0700, Ian Kelly wrote:
>> 
>>> On Thu, Mar 3, 2016 at 10:21 AM, alister <alister.ware@ntlworld.com>
>>> wrote:
>>>> On Thu, 03 Mar 2016 13:35:12 +1100, Chris Angelico wrote:
>>>>> 1) No physical object can have negative mass.
>>>>> 2) I am a part of the universe and have positive mass.
>>>>> 3) I am not Kenneth.
>>>>> 4) The sum of my mass and Kenneth's mass must exceed Kenneth's mass
>>>>> alone.
>>>>> 
>>>>> Unless someone wants to dispute 1 or 2, we can be logically certain.
>>>>> 
>>>>> ChrisA
>>>> 
>>>> Anti Matter?
>>> 
>>> Antimatter has positive mass.
>> 
>> Are you sure?
> 
> The ALPHA experiment at CERN is attempting a direct measurement of the
> mass of anti-hydrogen by trapping atoms of the stuff in a penning trap
> at high vacuum. The answer isn’t definitive yet as the error bars are
> huge and extend past zero, but are centered on the positive side.
> 
> -Bill
> 
> 
>> mix 1 atom of hydrogen + 1 of anti hydrogen & you end up with 0 mass (+
>> LOTTS of energy)
>> 
>> To be honest it is all over my head
>> 
>> 
>> 
>> --
>> I used to be Snow White, but I drifted.
>> 		-- Mae West
>> --
>> https://mail.python.org/mailman/listinfo/python-list



yes I have found some article that seem to agree with that.

it appears that anti-matter only has -v2 charges
something new & interesting learned today

-- 
"Wish not to seem, but to be, the best."
-- Aeschylus

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#104005 — [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

On Fri, 4 Mar 2016 07:20 am, alister wrote:

> On Thu, 03 Mar 2016 11:03:55 -0700, Ian Kelly wrote:

>> Antimatter has positive mass.
> 
> Are you sure?
>  mix 1 atom of hydrogen + 1 of anti hydrogen & you end up with 0 mass (+
> LOTTS of energy)
> 
> To be honest it is all over my head

It's good to be honest :-)


Yes, anti-matter has positive mass. There was still some tiny lingering
doubt up until (by memory) 20 years ago, at which time physicists actually
managed to make sufficient anti-matter that they could assemble it into
slow-moving atoms and observe the effect of gravity on it, and sure enough,
anti-matter falls due to gravity the same as regular matter.

(There wasn't really any serious doubt about this, since you can pull and
push anti-matter with electric and magnetic fields and it behaves exactly
the same way as regular matter. But if gravity had turned out to be
different, it would have been a truly paradigm-changing discovery.)

As far as the reaction of matter and anti-matter, we've known for about a
century that mass and energy are related and freely convertible from one to
the other. That's the famous equation by Einstein: E = m*c**2. Even tiny
amounts of energy (say, the light and heat released from a burning match)
involve a correspondingly tiny reduction in mass.


-- 
Steven

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#104021 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

On 4 March 2016 at 00:04, Steven D'Aprano <steve@pearwood.info> wrote:
> On Fri, 4 Mar 2016 07:20 am, alister wrote:
>
>> On Thu, 03 Mar 2016 11:03:55 -0700, Ian Kelly wrote:
>
>>> Antimatter has positive mass.
>>
>> Are you sure?
>>  mix 1 atom of hydrogen + 1 of anti hydrogen & you end up with 0 mass (+
>> LOTTS of energy)

This is incorrect. Mass and energy are both conserved. In a
particle/antiparticle annihilation new particles are created. See
here:
https://en.wikipedia.org/wiki/Annihilation

The mass is carried by the new particles. The new particles may have a
total *rest mass* which differs from the total rest mass of the
previous particles. However the total mass is the rest mass plus the
mass associated with the "kinetic energy" of the particles.

> As far as the reaction of matter and anti-matter, we've known for about a
> century that mass and energy are related and freely convertible from one to
> the other. That's the famous equation by Einstein: E = m*c**2. Even tiny
> amounts of energy (say, the light and heat released from a burning match)
> involve a correspondingly tiny reduction in mass.

This is also incorrect and suffers from the same misinterpretation as
above. Mass and energy are not interchangeable in the sense that you
can exchange one for the other with e=mc^2 giving the exchange rate.
Rather mass and energy are *the same thing*. Although they are
different concepts defined in different ways and having different
dimensions and units they are inseparable: e=mc^2 gives us the
proportion in which the two appear together.

--
Oscar

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#104023 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

Oscar Benjamin <oscar.j.benjamin@gmail.com>:

> The mass is carried by the new particles. The new particles may have a
> total *rest mass* which differs from the total rest mass of the
> previous particles. However the total mass is the rest mass plus the
> mass associated with the "kinetic energy" of the particles.
>
> [...]
>
> Mass and energy are not interchangeable in the sense that you can
> exchange one for the other with e=mc^2 giving the exchange rate.
> Rather mass and energy are *the same thing*. Although they are
> different concepts defined in different ways and having different
> dimensions and units they are inseparable: e=mc^2 gives us the
> proportion in which the two appear together.

A physicist mentioned to me that the word "mass" has replaced the term
"rest mass" in modern Physics lingo. That's why you say a photon is
"massless" even though every observable photon has a relativistic mass.
It's all in the terminology.

As for the existence of a negative mass, it is interesting to note that
the (rest) mass of an alpha particle is less than the sum of the (rest)
masses of its constituents. About 1% of the mass is "missing."


Marko

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#104034 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

On Fri, 04 Mar 2016 12:38:28 +0200, Marko Rauhamaa wrote:

> As for the existence of a negative mass, it is interesting to note
> that the (rest) mass of an alpha particle is less than the sum of the
> (rest) masses of its constituents. About 1% of the mass is "missing."

https://en.wikipedia.org/wiki/Binding_energy

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#104044 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

On 4 March 2016 at 10:38, Marko Rauhamaa <marko@pacujo.net> wrote:
> Oscar Benjamin <oscar.j.benjamin@gmail.com>:
>
>> The mass is carried by the new particles. The new particles may have a
>> total *rest mass* which differs from the total rest mass of the
>> previous particles. However the total mass is the rest mass plus the
>> mass associated with the "kinetic energy" of the particles.
>>
>> [...]
>>
>> Mass and energy are not interchangeable in the sense that you can
>> exchange one for the other with e=mc^2 giving the exchange rate.
>> Rather mass and energy are *the same thing*. Although they are
>> different concepts defined in different ways and having different
>> dimensions and units they are inseparable: e=mc^2 gives us the
>> proportion in which the two appear together.
>
> A physicist mentioned to me that the word "mass" has replaced the term
> "rest mass" in modern Physics lingo.

It depends on the context. Rest mass or similar can still be used
where you want to stress the difference (as I was doing).

> That's why you say a photon is
> "massless" even though every observable photon has a relativistic mass.
> It's all in the terminology.

That's just a casual use of terminology. If we want to be precise then
it's pointless to even refer to the "rest mass" of something that is
never at rest. The masslessness of photons comes from an extrapolation
that leads to a divide by infinity: strictly speaking it's just
undefined.

> As for the existence of a negative mass, it is interesting to note that
> the (rest) mass of an alpha particle is less than the sum of the (rest)
> masses of its constituents. About 1% of the mass is "missing."

Since the binding is associated with negative energy it has a negative
contribution to the energy/mass of the particle as a whole. This is
true of any bound state.

Something I don't know is if there's some theoretical reason why the
binding energy could never exceed the sum of the energies of the
constituent particles (resulting in an overall negative mass).

--
Oscar

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#104050 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

This discussion about energy and masses of particles has nothing to do with Python, and I am hoping that it will be dropped.  That being said, I feel compelled to correct what are completely wrong statements.

On Friday, 4 March 2016 13:36:11 UTC-4, Oscar Benjamin  wrote:
> On 4 March 2016 at 10:38, Marko Rauhamaa <marko@pacujo.net> wrote:
> > Oscar Benjamin <oscar.j.benjamin@gmail.com>:
> >
...
> 
> That's just a casual use of terminology. If we want to be precise then
> it's pointless to even refer to the "rest mass" of something that is
> never at rest. The masslessness of photons comes from an extrapolation
> that leads to a divide by infinity: strictly speaking it's just
> undefined.

This is simply wrong.  In Quantum Field Theory, particles can have "bare" mass term included in the Lagrangian and the measured mass either includes the bare mass + quantum corrections OR is a purely dynamically generated term.

In the Standard Model, there is no bare mass term for the photon, nor is there any dynamically generated mass.  In fact, to preserve gauge invariance symmetry, the mass of the photon MUST be identically equal to zero.

(Of course, the Standard Model could be incorrect but all meausurements done so far are completely consistent with a massless photon; see http://pdg.lbl.gov/2015/listings/rpp2015-list-photon.pdf for current experimental limits.)


> 
> > As for the existence of a negative mass, it is interesting to note that
> > the (rest) mass of an alpha particle is less than the sum of the (rest)
> > masses of its constituents. About 1% of the mass is "missing."
> 
> Since the binding is associated with negative energy it has a negative
> contribution to the energy/mass of the particle as a whole. This is
> true of any bound state.
> 
> Something I don't know is if there's some theoretical reason why the
> binding energy could never exceed the sum of the energies of the
> constituent particles (resulting in an overall negative mass).

The (magnitude of the) binding energy is DEFINED as the difference between the (energy equivalent) sums of the individual masses of the consistuents and that of the bound state.

===
Now, could we forget about Physics and go back to discussions related to Python?

André Roberge


> 
> --
> Oscar

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#104075 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

Oscar Benjamin wrote:
> If we want to be precise then
> it's pointless to even refer to the "rest mass" of something that is
> never at rest.

Which just shows that the term "rest mass" is a bit silly.
It came from some confused thinking very early in the
development of relativity. The physicists soon sorted that
out, but unfortunately the textbooks didn't catch up, and
we've ended up with several generations of confused
students as a result. :-(

  The masslessness of photons comes from an extrapolation
> that leads to a divide by infinity: strictly speaking it's just
> undefined.

No, it's not. The total energy of a particle is given by

    E**2 == c**2 * p**2 + m**2 * c**4

where p is the particle's momentum and m is its mass.
For a photon, m == 0. No division by zero involved.

For a massive particle at rest, p == 0 and the above
reduces to the well-known

    E == m * c**2

> Something I don't know is if there's some theoretical reason why the
> binding energy could never exceed the sum of the energies of the
> constituent particles (resulting in an overall negative mass).

Conservation of energy would be one reason. If you
put two particles together and got more energy out than
went in, where did the extra energy come from?

If you find a way to make that trick work, watch out --
the secret cartel of energy companies that's suppressing
all the free-energy inventions will want to disappear
you...

-- 
Greg

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#104077 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

On Sat, Mar 5, 2016 at 1:51 PM, Gregory Ewing
<greg.ewing@canterbury.ac.nz> wrote:
> Conservation of energy would be one reason. If you
> put two particles together and got more energy out than
> went in, where did the extra energy come from?

You borrowed it from the bank, of course. You have to make loan
payments periodically, or they'll foreclose on your particles. If
everyone borrows energy all at once, and then can't make their
payments, the universe crashes in a "heat death".

ChrisA

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#104088 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

Chris Angelico <rosuav@gmail.com>:

> On Sat, Mar 5, 2016 at 1:51 PM, Gregory Ewing
> <greg.ewing@canterbury.ac.nz> wrote:
>> Conservation of energy would be one reason. If you put two particles
>> together and got more energy out than went in, where did the extra
>> energy come from?
>
> You borrowed it from the bank, of course. You have to make loan
> payments periodically, or they'll foreclose on your particles. If
> everyone borrows energy all at once, and then can't make their
> payments, the universe crashes in a "heat death".

Quantum Mechanics works like a corrupt central bank: you have an
unlimited credit line and can borrow energy out of nothing as long as
you repay the loan before the audit.


Marko

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#104095 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

On 5 March 2016 at 02:51, Gregory Ewing <greg.ewing@canterbury.ac.nz> wrote:
>  The masslessness of photons comes from an extrapolation
>>
>> that leads to a divide by infinity: strictly speaking it's just
>> undefined.
>
> No, it's not. The total energy of a particle is given by
>
>    E**2 == c**2 * p**2 + m**2 * c**4
>
> where p is the particle's momentum and m is its mass.
> For a photon, m == 0. No division by zero involved.
>
> For a massive particle at rest, p == 0 and the above
> reduces to the well-known
>
>    E == m * c**2

The distinction I'm drawing is between physical fact and mathematical
convenience. For other particles we can say that the 1st formula above
holds with m taken to be the mass of the particle at rest. We can
extend that formula to the case of photons which are never at rest by
saying that in the case of photons m=0. That's nice and it's
mathematically convenient in the calculations. It's analogous to
extending the natural definition of the factorial function by saying
that 0!=1. We can't prove that 0!=1 but it's useful to define it that
way. It wouldn't be a disaster to simply leave 0! undefined: it would
just make some equations a little more complicated.

Since the generally accepted physical fact is that photons are never
at rest we are free to define their "rest mass" (use any term you
like) to be anything that is mathematically convenient so we define it
as zero because that fits with your equation above. Turning full
circle we can then use the equation above to say that they are
massless since they would hypothetically be massless in some other
situation even though genuinely massless photons are not thought to
exist in physical reality (unless I'm really out of date on this!).

>> Something I don't know is if there's some theoretical reason why the
>> binding energy could never exceed the sum of the energies of the
>> constituent particles (resulting in an overall negative mass).
>
> Conservation of energy would be one reason. If you
> put two particles together and got more energy out than
> went in, where did the extra energy come from?

That's the point: the energy balance would be satisfied by the
negative energy of the bound particles. The binding energy can be
defined as the energy required to unbind the particles (other
definitions such as André's are also possible). From this definition
we see that the binding energy depends on the binding interaction
(electromagnetic or whatever) that binds the particles together.

The only examples I know of where the binding energy is computed
approximately for e.g. a hydrogen atom predict that the binding energy
is proportional to the (rest) mass of the bound particle(s). If it's
guaranteed that the binding energy always somehow comes out
proportional to the mass of the particles with a coefficient
necessarily smaller than 1/c**2 then you could say that the bound
product could never have negative energy. I just can't see off the top
of my head an argument to suggest that this is impossible.

--
Oscar

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#104100 — Photon mass (was: [Still off-top] Physics)

Oscar Benjamin wrote:

> On 5 March 2016 at 02:51, Gregory Ewing <greg.ewing@canterbury.ac.nz>
> wrote:
>>>  The masslessness of photons comes from an extrapolation
>>> that leads to a divide by infinity: strictly speaking it's just
>>> undefined.
>>
>> No, it's not. The total energy of a particle is given by
>>
>>    E**2 == c**2 * p**2 + m**2 * c**4
>>
>> where p is the particle's momentum and m is its mass.
>> For a photon, m == 0. No division by zero involved.
>>
>> For a massive particle at rest, p == 0 and the above
>> reduces to the well-known
>>
>>    E == m * c**2
> 
> The distinction I'm drawing is between physical fact and mathematical
> convenience.

The physical fact is that as far as we know the photon mass is zero.  That 
is, the upper limit of the photon mass is so close to zero (at the time of 
writing, Adelberger et al. place it at < 10⁻²⁶ eV∕c² ≈ 1.783 × 10⁻⁵⁹ g 
≈ 1.957 × 10⁻³² m_e; see below) that we can assume it to be zero without 
introducing significant error in our *physical* calculations.

<http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html>;
but also <http://pdg.lbl.gov/2015/listings/rpp2015-list-photon.pdf> pp.,
and in general <http://pdg.lbl.gov> → “Summary Tables” → “Gauge and Higgs 
Bosons”.

> […]
> Since the generally accepted physical fact is that photons are never
> at rest

ISTM that this is rather a mathematical fact following from that energy–
momentum relation and the assumption that the photon (γ) mass m_γ is zero.  
It follows rather obviously then that E(m = m_γ = 0, p = 0) = 0.  But 
everything that exists has to have some (non-zero) energy.  So photons, and 
in general any objects, that have no mass *and* no momentum relative to a 
frame of reference cannot exist for an observer at rest relative to that 
frame.

> we are free to define their "rest mass" (use any term you
> like) to be anything that is mathematically convenient so we define it
> as zero because that fits with your equation above.

No.  We know that if our present understanding of physics is a sufficiently 
complete/correct description of reality, m_γ = 0 is a requirement.

Several reasons for that can be given; here are some:

1) If m_γ ≠ 0, the speed of light in vacuum could not be c as, according to 
special relativity, nothing that has mass m ≠ 0 can move at c relative to a 
frame of reference ­­– infinite energy in terms of that frame would be 
required for accelerating it to that speed: The kinetic energy of such a 
body is

  Eₖ = E_rel − E₀

where

  E₀ = E(m ≠ 0, p = 0) = mc²

by the energy–momentum relation (see above), and

  lim E_rel(v) = lim mc²∕√(1 − (v∕c)²) = +∞
  v→c            v→c

–, and photons are the particles of *light*.  So m = m_γ ≠ 0 would have 
profound and measurable implications on the propagation of light, that would 
*at the very least* be inconsistent with our knowledge of optics that 
precedes special relativity.

<https://en.wikipedia.org/wiki/Kinetic_energy#Relativistic_kinetic_energy_of_rigid_bodies>

2) When one looks into

  E² = (p c)² + (m c²)²

further – which is not just an arbitrary equation that happens to fits 
observations very well, but is derived from the norm of the four-momentum –, 
one realizes that if, and only if,

  m_γ = 0,

then also

  E_γ = E(m = m_γ, p) = p c = ℏk c = ℎc/λ = ℎf

(ℏ = ℎ∕2π, k = ||k⃗|| = 2π∕λ — wavenumber, k⃗ — wave vector), which has been 
experimentally confirmed even *before* the postulation of special relativity 
in observations of the photoelectric effect (the kinetic energy imparted by 
light to electrons in a metal’s surface is proportional to its wavelength 
λ/frequency f).  So if m_γ ≠ 0, this would also have profound and measurable 
implications on the energy transported by light of different 
wavelengths/frequencies/colors that would be inconsistent with our knowledge 
of electromagnetic radiation that precedes special relativity.

<https://en.wikipedia.org/wiki/Energy%E2%80%93momentum_relation#Norm_of_the_four-momentum>
<https://en.wikipedia.org/wiki/Planck_constant>

Finally,

3) if m_γ ≠ 0, the range of the electromagnetic interaction would not be 
infinite, as because of the uncertainty principle the range r of an 
interaction depends on the mass m of the particle that carries it:

  r(m) ≈ c∆t ≈ ℏ∕2mc.

This would have profound and measurable implications on fundamental 
interactions that would be inconsistent with our experimentally very well 
confirmed (and daily applied) knowledge of quantum mechanics.

<http://hyperphysics.phy-astr.gsu.edu/hbase/forces/exchg.html>


X-Post & F'up2 sci.physics.relativity

-- 
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

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#104098 — Re: [Still off-top] Physics [was Requests author discusses MentalHealthError exception]

On Saturday 05 March 2016 08:11:46 Oscar Benjamin wrote:

> On 5 March 2016 at 02:51, Gregory Ewing <greg.ewing@canterbury.ac.nz> 
wrote:
> >  The masslessness of photons comes from an extrapolation
> >
> >> that leads to a divide by infinity: strictly speaking it's just
> >> undefined.
> >
> > No, it's not. The total energy of a particle is given by
> >
> >    E**2 == c**2 * p**2 + m**2 * c**4
> >
> > where p is the particle's momentum and m is its mass.
> > For a photon, m == 0. No division by zero involved.
> >
> > For a massive particle at rest, p == 0 and the above
> > reduces to the well-known
> >
> >    E == m * c**2
>
> The distinction I'm drawing is between physical fact and mathematical
> convenience. For other particles we can say that the 1st formula above
> holds with m taken to be the mass of the particle at rest. We can
> extend that formula to the case of photons which are never at rest by
> saying that in the case of photons m=0. That's nice and it's
> mathematically convenient in the calculations. It's analogous to
> extending the natural definition of the factorial function by saying
> that 0!=1. We can't prove that 0!=1 but it's useful to define it that
> way. It wouldn't be a disaster to simply leave 0! undefined: it would
> just make some equations a little more complicated.
>
> Since the generally accepted physical fact is that photons are never
> at rest we are free to define their "rest mass" (use any term you
> like) to be anything that is mathematically convenient so we define it
> as zero because that fits with your equation above. Turning full
> circle we can then use the equation above to say that they are
> massless since they would hypothetically be massless in some other
> situation even though genuinely massless photons are not thought to
> exist in physical reality (unless I'm really out of date on this!).
>
> >> Something I don't know is if there's some theoretical reason why
> >> the binding energy could never exceed the sum of the energies of
> >> the constituent particles (resulting in an overall negative mass).
> >
> > Conservation of energy would be one reason. If you
> > put two particles together and got more energy out than
> > went in, where did the extra energy come from?
>
> That's the point: the energy balance would be satisfied by the
> negative energy of the bound particles. The binding energy can be
> defined as the energy required to unbind the particles (other
> definitions such as André's are also possible). From this definition
> we see that the binding energy depends on the binding interaction
> (electromagnetic or whatever) that binds the particles together.
>
> The only examples I know of where the binding energy is computed
> approximately for e.g. a hydrogen atom predict that the binding energy
> is proportional to the (rest) mass of the bound particle(s). If it's
> guaranteed that the binding energy always somehow comes out
> proportional to the mass of the particles with a coefficient
> necessarily smaller than 1/c**2 then you could say that the bound
> product could never have negative energy. I just can't see off the top
> of my head an argument to suggest that this is impossible.
>
> --
> Oscar

I've never heard of a massless photon, and they do exert a push on the 
surface they are reflected from, its even been proposed to use it as a 
space drive.  The push is miniscule indeed at normal illumination levels 
but some have calculated how much laser power it would take to move 
something like a solar sail. Practically, the cost of the energy and the 
size of the laser needed are impractical.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

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#104102 — Photon mass (was: [Still off-top] Physics)

Gene Heskett wrote:

> I've never heard of a massless photon,

That is unfortunate as it should be common knowledge by now.

> and they do exert a push on the surface they are reflected from, […]

Photons exert a force on surfaces because they carry *momentum* or, as it 
had been understood in terminology that is obsolete now, a non-zero 
“*relativistic* mass” (that had been distinguished from “rest mass”).

<https://en.wikipedia.org/wiki/Mass#Mass_in_relativity>
<https://en.wikipedia.org/wiki/Mass_in_special_relativity#Relativistic_mass>

F'up2 sci.physics.relativity

-- 
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

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#104139 — Re: Photon mass (was: [Still off-top] Physics)

On Saturday 05 March 2016 10:46:04 Thomas 'PointedEars' Lahn wrote:

> Gene Heskett wrote:
> > I've never heard of a massless photon,
>
> That is unfortunate as it should be common knowledge by now.
>
> > and they do exert a push on the surface they are reflected from, […]
>
> Photons exert a force on surfaces because they carry *momentum* or, as
> it had been understood in terminology that is obsolete now, a non-zero
> “*relativistic* mass” (that had been distinguished from “rest mass”).
>
To have "momentum" imply's mass in the real, we can measure it world.

However with my lack of education, I have a hard time reconciling that 
they travel at C speed, when the classical math says that anything with 
mass traveling at C speed will have aborbed enough energy in getting to 
C speed, that its mass is then infinite. But its obviously not.

I once used relativity to explain to a degree'd FCC engineer exactly why 
a UHF transmitter that used klystrons for amnplifiers, alway had a 
backgound audio buzz. At the moment this was taking place, the station  
was crippled as we'd had a circuit breaker failure, single phasing and 
stopping the cooling water pump, which in turn destroyed the klystron 
used as a visual amplifier (one circuit breaker boom as the building 
went dark when the tube filled with steam, byby $120,000 USD), so just 
to stay on the air, I had moved a weak & about used up klystron from the 
aural cabinet to the visual cabinet, and tee connected the aural drive 
into the visual drive.

When the engineer came in the door, one of the first things he had 
noticed when he monitored the station from about 15 miles away the 
previous evening, was that we were a UHF, but didn't have that annoying 
background buzz in the sound.  So I had to explain it.

What we were observing was that by combining the two carrier signals into 
one tube, meant that both signals were being treated equally to the  
phenomenon they had called incidental carrier phase modulation, and its 
created in the amplitude modulated signal because the 4 foot long 
electron beam is traveling at a speed where speed vs mass is beginning 
to make itself measureable. Said simply, the tube amplifies the signal 
by nominally 30db, by introducing an electrical field across the input 
cavities gap that alternately speeds up, or slows down, an electron 
traverseing that gap with a 20 kilovolt induced speed. 4 feet and  3 
more cavities later, those electrons are now bunched up, the ones in 
front slowing to fall into the bunch, and the ones behind being pushed 
to catch up with the bunch. That induces, because the beam is something 
north of 5 amps, a considerable amount of power in the last cavity which 
can be coupled back out and sent to the antenna, typically about 30 kw.

However, because this beam of electrons is traveling fast enough for 
relativity to come into play, the energy applied to speed the beam up 
encounters an electron with higher mass as it accelerates, whereas the 
energy applied to slow it encounters an electron with lower mass, so the 
deceleration is fractionally greater.  IOW, its not perfectly 
symetrical, the net effect being that the average speed of the beam is 
instantaneous power level dependent, the tube being effectively, 
physically longer, with a longer transit time as the power level rises.
This is efffectively a frequency modulation, and an unwanted effect.

Some circuits, once the cause of the phenom was known, were designed to 
predistort this by intruducing an opposing FM and cancel it, but by then 
the heyday of the klysron amplifier was coming to an end because of its 
horrible efficiency, that 30 kw of output came at a cost of a few hairs 
over 100kw in the beam supply, making a UHF transmitter the local power 
companies largest customer by a fairly wide margin. That tramsitter used 
nearly 200 kw for every hour it was on the air, and multi-thousand 
dollar power bills were getting the bean counters attention.

But when both signals, visual and aural, are subjected to the same 
effect, AND the sound detection is based on the FM of the 4.5 megahertz 
difference, it cancels out in the receiver. Later, while still operating 
crippled, I made some aural signal to noise measurements, finding truely 
amazing figures of nearly 80 db with video still applied, where when 
operating with 2 klystrons as intended, it was hard put to make a bit 
over 50 db.  It was such a problem that the FCC allowed us to make those 
measurements with the baseband video cable unplugged when doing a proof 
of performance, required for license renewal every 5 years back in those 
days.

So in that scenario, I have first hand knowledge about relativity despite 
my offical 8th grade education. Photons not having a mass but can exert 
a push isn't something this 81 yo wet ram can quite figure out.  In my 
mind, when the ball bounces, its mass exerts a push on the wall it was 
bounced off of.  For a photon to do that, requires it have a mass, 
however miniscule it might be, possibly just the mass of the light 
energy its carrying.  Can that be quantified to a known value, probably 
color dependent?
> <https://en.wikipedia.org/wiki/Mass#Mass_in_relativity>
> <https://en.wikipedia.org/wiki/Mass_in_special_relativity#Relativistic
>_mass>
>
> F'up2 sci.physics.relativity
>
> --
> PointedEars
>
> Twitter: @PointedEars2
> Please do not cc me. / Bitte keine Kopien per E-Mail.


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

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#104159 — Re: Photon mass (was: [Still off-top] Physics)

On Sat, 5 Mar 2016 12:36:14 -0500, Gene Heskett <gheskett@wdtv.com>
declaimed the following:

>however miniscule it might be, possibly just the mass of the light 
>energy its carrying.  Can that be quantified to a known value, probably 
>color dependent?

	Color implies frequency/wavelength... Higher frequencies => higher
energies

https://en.wikipedia.org/wiki/Photon_energy
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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#104173 — Re: Photon mass (was: [Still off-top] Physics)

On Sat, Mar 5, 2016 at 12:36 PM, Gene Heskett <gheskett@wdtv.com> wrote:
> On Saturday 05 March 2016 10:46:04 Thomas 'PointedEars' Lahn wrote:
>
>> Gene Heskett wrote:
>> > I've never heard of a massless photon,
>>
>> That is unfortunate as it should be common knowledge by now.
>>
>> > and they do exert a push on the surface they are reflected from, […]
>>
>> Photons exert a force on surfaces because they carry *momentum* or, as
>> it had been understood in terminology that is obsolete now, a non-zero
>> “*relativistic* mass” (that had been distinguished from “rest mass”).
>>
> To have "momentum" imply's mass in the real, we can measure it world.
>
> However with my lack of education, I have a hard time reconciling that
> they travel at C speed, when the classical math says that anything with
> mass traveling at C speed will have aborbed enough energy in getting to
> C speed, that its mass is then infinite. But its obviously not.
>
> I once used relativity to explain to a degree'd FCC engineer exactly why
> a UHF transmitter that used klystrons for amnplifiers, alway had a
> backgound audio buzz. At the moment this was taking place, the station
> was crippled as we'd had a circuit breaker failure, single phasing and
> stopping the cooling water pump, which in turn destroyed the klystron
> used as a visual amplifier (one circuit breaker boom as the building
> went dark when the tube filled with steam, byby $120,000 USD), so just
> to stay on the air, I had moved a weak & about used up klystron from the
> aural cabinet to the visual cabinet, and tee connected the aural drive
> into the visual drive.
>
> When the engineer came in the door, one of the first things he had
> noticed when he monitored the station from about 15 miles away the
> previous evening, was that we were a UHF, but didn't have that annoying
> background buzz in the sound.  So I had to explain it.
>
> What we were observing was that by combining the two carrier signals into
> one tube, meant that both signals were being treated equally to the
> phenomenon they had called incidental carrier phase modulation, and its
> created in the amplitude modulated signal because the 4 foot long
> electron beam is traveling at a speed where speed vs mass is beginning
> to make itself measureable. Said simply, the tube amplifies the signal
> by nominally 30db, by introducing an electrical field across the input
> cavities gap that alternately speeds up, or slows down, an electron
> traverseing that gap with a 20 kilovolt induced speed. 4 feet and  3
> more cavities later, those electrons are now bunched up, the ones in
> front slowing to fall into the bunch, and the ones behind being pushed
> to catch up with the bunch. That induces, because the beam is something
> north of 5 amps, a considerable amount of power in the last cavity which
> can be coupled back out and sent to the antenna, typically about 30 kw.
>
> However, because this beam of electrons is traveling fast enough for
> relativity to come into play, the energy applied to speed the beam up
> encounters an electron with higher mass as it accelerates, whereas the
> energy applied to slow it encounters an electron with lower mass, so the
> deceleration is fractionally greater.  IOW, its not perfectly
> symetrical, the net effect being that the average speed of the beam is
> instantaneous power level dependent, the tube being effectively,
> physically longer, with a longer transit time as the power level rises.
> This is efffectively a frequency modulation, and an unwanted effect.
>
> Some circuits, once the cause of the phenom was known, were designed to
> predistort this by intruducing an opposing FM and cancel it, but by then
> the heyday of the klysron amplifier was coming to an end because of its
> horrible efficiency, that 30 kw of output came at a cost of a few hairs
> over 100kw in the beam supply, making a UHF transmitter the local power
> companies largest customer by a fairly wide margin. That tramsitter used
> nearly 200 kw for every hour it was on the air, and multi-thousand
> dollar power bills were getting the bean counters attention.
>
> But when both signals, visual and aural, are subjected to the same
> effect, AND the sound detection is based on the FM of the 4.5 megahertz
> difference, it cancels out in the receiver. Later, while still operating
> crippled, I made some aural signal to noise measurements, finding truely
> amazing figures of nearly 80 db with video still applied, where when
> operating with 2 klystrons as intended, it was hard put to make a bit
> over 50 db.  It was such a problem that the FCC allowed us to make those
> measurements with the baseband video cable unplugged when doing a proof
> of performance, required for license renewal every 5 years back in those
> days.
>
> So in that scenario, I have first hand knowledge about relativity despite
> my offical 8th grade education.

Gene, your massive and varied experiences trump my formal education any day.

>Photons not having a mass but can exert
> a push isn't something this 81 yo wet ram can quite figure out.  In my
> mind, when the ball bounces, its mass exerts a push on the wall it was
> bounced off of.  For a photon to do that, requires it have a mass,
> however miniscule it might be, possibly just the mass of the light
> energy its carrying.  Can that be quantified to a known value, probably
> color dependent?

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#104119 — Re: [Still off-topic] Physics

On Fri, 4 Mar 2016 09:19 pm, Oscar Benjamin wrote:

>> As far as the reaction of matter and anti-matter, we've known for about a
>> century that mass and energy are related and freely convertible from one
>> to the other. That's the famous equation by Einstein: E = m*c**2. Even
>> tiny amounts of energy (say, the light and heat released from a burning
>> match) involve a correspondingly tiny reduction in mass.
> 
> This is also incorrect and suffers from the same misinterpretation as
> above. Mass and energy are not interchangeable in the sense that you
> can exchange one for the other with e=mc^2 giving the exchange rate.

Hmmm. Well, it's actually a bit more complicated than that. It depends by
what you mean by "converting" mass to energy. We can give at least one
sense in which it is true that mass is converted to energy, and likewise at
least one in which is it not true.

For example, we might say that even if mass-energy equivalence means that
mass and energy are in fact the same sort of thing, we can nevertheless
convert from one to another in the same way that one can convert from
kinetic energy to potential energy, or heat energy to rotational energy.

The Stanford Encyclopedia of Philosophy has a good discussion of the various
interpretations of mass-energy equivalence:

http://plato.stanford.edu/entries/equivME/


And of course, regardless of whether or not mass "really is" converted to
energy or not, using the language of conversion is the standard way to talk
about it:

https://www.physicsforums.com/threads/energy-mass-conversion.177827/

Unfortunately, mass is one of those concepts that seems easy to define, but
actually is anything but!

http://www.physics-online.ru/MessageFiles/6642/EJP-Roche-05.pdf


> Rather mass and energy are *the same thing*. Although they are
> different concepts defined in different ways and having different
> dimensions and units they are inseparable: e=mc^2 gives us the
> proportion in which the two appear together.

So apart from being different concepts defined in different ways with
different dimensions and different units, they're exactly the same?

Right-o.


Wikipedia says:

"... mass–energy equivalence is a concept formulated by Albert Einstein that
explains the relationship between mass and energy. It states every mass has
an energy equivalent and vice versa ..."

https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence

but beware because the Wikipedia article "appears to contradict itself".

Mass-energy equivalence is a simple formula, an important formula, and well
understood in practice. But what it actually "means" in theory is anyone's
guess. And so, on the principle that an analogy that is utterly wrong in a
technical sense but understandable is better than a complicated and complex
explanation that is utterly incomprehensible, I'm going to stick to talking
about mass/energy conversions :-)



-- 
Steven

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