# Calling pmb_phy

1. ### Aer

214
I wish to converse with you on your brand of relativistic mass.

Pervect, can you direct me to the thread where pmb_phy convinced you relativistic mass was useful?

2. ### pmb_phy

There is no thread that convinced me of anything. I doubt there is one thread that can/should convince anyone of anything. Being that mallable on one's ideas in physics (science) is never a good idea. I came across this debate (not really much of a debate really) back about 15 years ago. Later in about 1997 some people were swearing by it and claiming everone used it and how rest mass was the only "real" mass yadda yadda yadda. I spent the following 7 years studying the subject to form an opinion. My opion is that if you want to give a meaning to the word "mass" then the term which posseses the inertial, passive gravitational and active gravitational mass then it is what you refer to as "relativistic mass."

If you want the details then read this
http://www.geocities.com/physics_world/mass_paper.pdf

Warning - I poorly proof read that work. It took so long to write that it had a ton of errors in it (few conceptual errors. only one that I'm aware of. just repetition and poor phrasing etc). I haven't gotten time to rerwrite it. Have fun - Warning. Its over 80 pages long.

The error I mention im my paper is when I made the assumption that E = mc^2 in all cases. A counter example is here
http://www.geocities.com/physics_world/sr/inertial_energy_vs_mass.htm

For more on why E != mc^2 in all cases see Rindler's text if you have a copy of it or access to it.

For other stuff see http://www.geocities.com/physics_world/misc/relativistic_mass.htm
http://www.geocities.com/physics_world/misc/mass_articles.htm

As far as anything else I'm pretty talked out of this topic and will simply be refering to that stuff inn the future. I've been rather sick for a while and don't have the strength for much posting.

Pete

Last edited: Jul 28, 2005
3. ### ohwilleke

703
You have our best wishes to get well. Take care.

4. ### pmb_phy

However there is Wheeler's First Moral Principle which states "Never make a calculation until you know the answer[/i]. This implies that you should seek ways of thinking such that you have an idea of what the answer should be and if you get something totally unexpected then you need to rethink or be happy in your surprise. For example; I read a paper which did a rather round about calculation to find an answer for the deflection of a particle. The reason for the answer didn't seem right. However when looked at with gravitomagnetism keeping in mind that the active gravitational mass = relativistic mass, then the reason be comes clear.

If you can get a good idea of an amount without calculation then you've made a good jump in your knowledge and understanding of a subject.

Peter

5. ### Aer

214

Well, we shall create one.

Being completely wrong is never a good idea either.

Tell me, what is your definition of mass? Just mass, no adjectives or anything - I just want to know your definition of mass so we can work from there.

I've seen your paper and do not agree with it. So like I said, lets start with the definition of mass. Give me your definition.

Yeah, let's not refer to long winded discussions on the internet. You should be able to back up any argument on your own without refering to authority or your own work published elsewhere. I mean, we are talking about one basic concept - mass. So, what do you define mass to be - a concise answer is what I am looking for.

6. ### εllipse

195
Objects have proper lengths and clocks measure proper times, but we don't throw out the idea of relative lengths and times. Although a meter stick may still be a meter in your reference frame, if it's moving relative to me, it will have a relative length which is smaller. It's the same with mass. Invariant mass may be the most helpful concept from one viewpoint or relativistic mass may be the most helpful from another.

7. ### Aer

214
The proper length and contracted length are defined through the lorentz transformations. These are meaningful when dealing with "events" that happen in space-time.

To quote Einstein himself:

8. ### EnumaElish

2,483
Aer -- I "hear" doctor Einstein's quote. But on a purely technical note, one can define relativistic mass through a similar transformation: $M = \gamma \times m$, right? The concept may be misapplied, misdirected, improperly used, unbecoming of a physicist, auxiliary at best, etc., but there is a narrow technical sense in which one cannot say that M is ill-defined.

9. ### Aer

214
How wrong you are - it is technically an ill-defined quantity if it is in anyway refered to as "mass". Then we have people like pmb_phy claiming a contained gas's weight is a measure of the rest mass of the particles PLUS the kinetic energy they possess. UMMM - NO! That's wrong, the weight is only a measure of the rest mass of the particles and nothing more.

10. ### EnumaElish

2,483
One wonders, though, why and how could anyone come up with such a grand misconception? I mean, confusing mass and energy?! Thinking they could be the same? At best this is alchemy, if not outright heresy! Even I can understand something's wrong there, although I am no Einstein

Sorry, I couldn't contain myself.

11. ### Aer

214
Well, mass is a form of energy, yes. But mass has nothing to do with kinetic or potential energy.

12. ### learningphysics

4,124
pmb_phy is completely right. This has nothing to do with ill defined quantities.

When you measure your own weight on a scale... the number you get is not the sum of the rest masses of all the particles that make up your body... the number you get is much much higher than that.

The rest mass of a "set of particles" is not the sum of the rest masses of the constituent particles.

13. ### learningphysics

4,124
You really shouldn't insult someone who took the time to respond to your post despite the fact that he was tired of the topic.

Why should he bother? He's not trying to make any argument here... You asked for his input and he gave it to you. Then you turn around and insult him for it.

Last edited: Aug 4, 2005
14. ### Aer

214
learningphysics - based on my previous experience with you, I am going to assume you have no idea what you are talking about.

OK, I don't have to assume from memory anymore, here is a quote by you:

NO! And I am going to assume your misunderstanding stems from reading posts/websites by pmb_phy.

Last edited: Aug 4, 2005
15. ### Aer

214
I merely asked for his definition of mass. He can freely choose to ignore if he wishes.

16. ### JesseM

8,491
Are you sure about that? the last question from this FAQ says that the apparent inertia of a black box filled with a gas will increase as the temperature increases, which I would think would mean the weight would increase as well:
Also, in a post on this thread "Tom Roberts" describes the definition of rest mass for a composite object:
So, this would indicate that the rest mass of a box of gas is defined to be simply the sum of the relativistic masses of all the atoms in it, since this is equal to the total energy (assuming energy in other forms, like the potential energy between the particles that make up the atoms, can be ignored).

Last edited: Aug 4, 2005
17. ### Aer

214
From that same FAQ, that answer is to the following question: "Einstein said that if something could travel at light speed its mass would duplicate".

Einstein said that? No he didn't. That is just something that other people have wrongly interpreted from his equations.

If you wish to read something Einstein actually said:

If you are going to refer to authority, do so correctly next time.

18. ### JesseM

8,491
Yes, but FAQ questions do not represent the point of view of the author, only the answers do. And see the thing about the definition of the rest mass of a composite object I added in an edit.

Last edited: Aug 4, 2005
19. ### Aer

214
Who answered these questions? Was this person qualified? It would seem he is not qualified if he didn't correct the person asking the question as to what Einstein actually said.

20. ### learningphysics

4,124
Well here's another post of mine:

https://www.physicsforums.com/showpost.php?p=688394#post688394

I've posted links to course notes using the same definition of inertial mass.