Can mass be created or destroyed?

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physicsnewbie

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Sorry, I'm just a physics newbie.
 

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  • #2
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Well, the simple answer is matter cannot be created or destroyed.

The more complicated answer is that in some nuclear reactions particles can be converted into energy ( like in a hydrogen bomb). If that happened to your atoms you would said they were destroyed. If you consider the familiar equation E=mc2 it means there is an equivalence between matter and energy.

I'm sure someone else will give us a more complicated answer.:smile:
 
  • #3
FZ+
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mmwave: You mean yes, matter can be created or destroyed, right?

Other examples: matter-antimatter annihilation, pair production by energetic photon...

Correction: mass in the conventional sense can be destroyed, but mass/energy is conserved.
 
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  • #4
LURCH
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As far as we know, mass cannot be created or destroyed, it can only change form. Matter can become energy, and energy can become matter, but always according to e=m2. So, when a matter-antimatter reaction occurs, the mass of the matter (and antimatter) is converted to energy of equal mass, which propogates outward in verious forms (heat, light, a kinetic shockwave, sound waves, etc), and gets spread out thinner and thinner throughout the cosmos, but never looses anything in quantity. If you ever found a way to capture all the energy that was released in the reaction, and condense it back together into matter, you would have the same amount of mass as the original amount of material used.
 
  • #5
jcsd
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Mass means invariant mass and it can be destroyed and created that can be seen in the anihilation of a low energy and high energy electron-poistron pair (equation 1 is an anihilation of a low-energy pair whereas 2 and 3 are high energy pairs).

1) e+e- → γγ

2) e+e- → uû (π°) *

3) e+e- → μ+μ-


*I couldn't find the correct ascii symbols for antiquarks

In these equation the mass on left hand side of the equation totals 1.022 Mev/c2, but on the right hand-side the mass is 1)0 2)1.057 3)2.114, so obviously the mass has changed during these anhilations.

As long as you understand though that invariant mass is essientially 'mass-energy' and can be converted back and forth between other sorts of energy (e.g. K.E.).
 
  • #6
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Originally posted by FZ+
mmwave: You mean yes, matter can be created or destroyed, right?

Other examples: matter-antimatter annihilation, pair production by energetic photon...
No. In our everyday lives it is sufficient to say that matter is not destroyed. Your examples are for physics labs and stars and are really the conversion of energy to matter or matter to energy covered in my second paragraph. I believe the better way to look at it from a physics stand point is that matter is just a form of energy.
 
  • #7
jcsd
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btw can everyone see the character set I've used for the equations in my last post?

Just in case you can't, here's the equations in written form:

1) electron + positron -> two photons

2) electron + positron -> an up quark and an up antiquark (a neutral pion)

3) electron + positron -> a muon and an anti-muon
 
  • #8
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Hi Jcsd,

I could read your first character set so thanks for doing the ascii thing too. EDIT: could NOT read them

Why would they call it invariant mass if it can be converted to energy and disappear? That seems like variation to me. :smile:
 
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  • #9
Hurkyl
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It's invariant under Lorentz transformations; any two (inertial) observers will record the same invariant mass for an object, in contrast with things like speed, kinetic energy, or distance which generally vary between different observers.
 
  • #10
Ivan Seeking
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It seems that this issue of "invariant mass" and "mass" is really just a matter of definition.

What term can we use to address the "source" of inertia and gravity?

...if the term "mass" is now treated as meaning rest mass.

Does the concept of mass beyond this notion fail for some reason, or is this this merely a convention?

Perhaps the concept of mass, beyond rest mass, is thought to be simply unnecessary?
 
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  • #11
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Can mass be created or destroyed?



If it couldn't the bigbang would have never occured. People fail to realize that. They say that nothing existed before the big bang. Well if that's true then WHAT BLEW UP? :-) So either we deny physics its rules or throw bigbang out the window, the communities choice.
 
  • #12
jcsd
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Originally posted by Cyberice
Can mass be created or destroyed?



If it couldn't the bigbang would have never occured. People fail to realize that. They say that nothing existed before the big bang. Well if that's true then WHAT BLEW UP? :-) So either we deny physics its rules or throw bigbang out the window, the communities choice.
No all the matter aound today was there at the time of the bigbang contained within the singularity.
 
  • #13
russ_watters
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Originally posted by Cyberice
Can mass be created or destroyed?
So either we deny physics its rules or throw bigbang out the window, the communities choice.
Option A. It is a fundamental part of the Big Bang theory that the rules of science break down at a point just after the Big Bang. So the normal rules don't apply. The truth is we don't know where the matter came from. But it did come from the Big Bang.
 
  • #14
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Originally posted by FZ+
mmwave: You mean yes, matter can be created or destroyed, right?

Other examples: matter-antimatter annihilation, pair production by energetic photon...
How would you go about creating/destroying mass? What exactly would you do?
 
  • #15
jcsd
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Originally posted by Tail
How would you go about creating/destroying mass? What exactly would you do?
see my previous post. In 1) (invariant) mass is destroyed in 3) it is created
 
  • #16
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But that was not what I was asking, obviously. I'd like to know just how one can create or destroy matter.
 
  • #17
jcsd
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Originally posted by Tail
But that was not what I was asking, obviously. I'd like to know just how one can create or destroy matter.
Well, no it's not obvious that that wasn't what you were asking as those are a few of the ways of creating and destroying mass (matter).
 
  • #18
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Mass and energy are not things they're properties of a system. If you define your system to include all the products of the interacting particles then the mass and energy remain the same.

If a nuclear weapon is detonated in a vault the vault weighs the same before and after the detonation.
 
  • #19
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Originally posted by jcsd
Well, no it's not obvious that that wasn't what you were asking as those are a few of the ways of creating and destroying mass (matter).
I don't think so. In order for an act of creation to occur there must be a creator. I'd like to hear about such an act, with emphasis on what the creator would do to create mass.
 
  • #20
pmb
Originally posted by physicsnewbie
Sorry, I'm just a physics newbie.
The anwswer to this question depends on what you mean by "mass." There are two senses in which the term "mass" is used in physics. One is what some people call "relativistic mass" and the other ios what some people call "rest mass." And then it will depend on what you mean by the mass of a system of particles since this is often the case people speak of when they speak of the mass of a system.

In the following I'm assuming that energy is conserved which is almost always the case.


If you mean "relativistic mass" then the answer is that mass is always conserved - i.e. it's a constant. No matter how you count it the mass is conserved.

If you mean "rest mass" and then that too is conserved - *if* you defined the mass of a system of particles as the energy in the rest frame divided by c^2. If you simply add rest masses then no - mass is not conserved. Same with "invariant mass" since they're the same thing. But the system mass will depend on how you define it. Some people call the mass of a system the sum of the rest masses and some do it the other way

With regards to the mass = rest mass definition = Taylor and Wheeler explain all this in their text "Spacetime Physics - 2nd Ed" - the relavent part is online in my web site

See
http://www.geocities.com/physics_world/stp/stp.htm

I have permission to post that from the author.

jeff said that mass means invariant mass and if one defines invariant mass as the magnitude of the total 4-momentum then what jeff claims is not true. And mass is not always defined to mean invariant mass (counter examples from relativity texts are Rindler (2002), Mould (1994), D'Inverno(1992), French (1968), etc). Not even for a large majority of the time. And jeff also implied that invariant mass is not conserved and that's not true either. Since invariant mass is defined as the mass in the rest frame and then in the rest frame its defined as "energy in rest frame"/c^2 so since energy is conserved then so too is mass.

For a worked out example of mass to energy conversion (mass changes form but not value) see

http://www.geocities.com/physics_world/sr/nuclear_energy.htm

For an explantion of what invariant mass is and why it's conserved see

http://www.geocities.com/physics_world/sr/invariant_mass.htm

In the case jeff gave its rather easy to see why invariant mass "of the system" is conserved Since both


Pete
 
  • #21
pmb
Originally posted by mmwave
Well, the simple answer is matter cannot be created or destroyed.

The more complicated answer is that in some nuclear reactions particles can be converted into energy ( like in a hydrogen bomb). If that happened to your atoms you would said they were destroyed. If you consider the familiar equation E=mc2 it means there is an equivalence between matter and energy.

I'm sure someone else will give us a more complicated answer.:smile:
Particles are not converted into energy. What happens in nuclear reations is the the form of the energy changes. The energy is always constant

http://www.geocities.com/physics_world/sr/nuclear_energy.htm

You might have an electron and a positron anihilate resulting in photons being created but that's different. That's a change in the form of matter. One shouldn't think of a photon as being energy but rather a photon has energy - just as an electron and a positron does. The sum of the rest masses changes but the total (relativistic) mass remains constant. Same with the invariant mass of the system.

For example: electron-positron anihilation. Let the energy of each before anihlation be E_i/2 so the total enertgy before anihilation (which is both kinetic energy and rest energy) is E_i. Choose a frame of referance in which the total momentum is zero. Then the 4-momentum of the system is

P = (E/c, p) = (E_i/c, 0)

since energy and momentum are both conserved the 4-momentum after anihilation is

P (E_i/c, 0)

The invariant mass of the system is the magnitude of this 4-vector and has the value proportional to M = E_i/c^2 which is a constant - i.e. it has the same value before the anihilation as it does after.

See

http://www.geocities.com/physics_world/sr/invariant_mass.htm

for details.

Pete
 
  • #22
john shoemaker
"In The Beginning'

Some theory folks write of the probability of disappearance of a particle(without appearance of equivalent energy) The conservation of energy and momentum and a few other things has been observed in experiments( naturally limited in scale) Others write of quarks, the assembly of a few results in a particle.
In short, the question is still open in open minds. There are physicists who feel that it is close minded to only consider that creation happened "In The Beginning".
 
  • #23
john shoemaker
"In The Beginning'

Some theory folks write of the probability of disappearance of a particle(without appearance of equivalent energy) The conservation of energy and momentum and a few other things has been observed in experiments( naturally limited in scale) Others write of quarks, the assembly of a few results in a particle.
In short, the question is still open in open minds. There are physicists who feel that it is close minded to only consider that creation happened "In The Beginning".
 
  • #24
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Originally posted by Cyberice
Can mass be created or destroyed?



If it couldn't the bigbang would have never occured. People fail to realize that. They say that nothing existed before the big bang. Well if that's true then WHAT BLEW UP? :-) So either we deny physics its rules or throw bigbang out the window, the communities choice.
The Big Bang theory does not state that there was nothing before.

There are inflation models that are without begin/end.
 
  • #25
Rog
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Originally posted by Cyberice
Can mass be created or destroyed?


Hmm It depends what you mean by created? From articles I have read in the past it is possible for a particle to pop into exsistence but it has to borrow energy from our system. This is a short lived life and quickly has to pay back the energy it borrowed.

Basically mass in the form of the particle has been created but from the energy already existent in the universe i.e. the total energy within the universe remains the same before and after the existence of the particle.
 

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