a Thinking Man's discussion

[swansont]

Measurements... from a frame of reference...

 

Yes, what you measure depends on your frame of reference. And you can tell if you are accelerating or not.

 

 

I'm not sure what you mean by "force". The whole point of the conservation laws is to say that the total measurements of a system persist across any possible interaction, including collisions. It's only supposed to "fail" when an external force is involved. And remember, this was all first implied by Newton, who believed that we live in a universe with an absolute frame of reference.

 

No, not any interaction, internal interactions. You have to define what is internal and external to your system. By choosing ball-1 to be your coordinate system, you have chosen everything else to be external. So a collision is an external force.

 

Yes, an inertial coordinate system... meaning an absolute one. But it still fails relativistically.

 

No, an inertial system is not an absolute one.

[galaxyblur]

But relativity says that one could claim to be accelerating themselves, or that everything else is accelerating and you are static. Every frame is equally valid.

 

So, by your logic, if we chose the Sun as our coordinate system (the solar system, in other words), all of the planets are now external? Maybe you're just repeating what you've heard and learned, but this makes no sense to me. Relatively speaking, there's no such thing as "external" or "internal". That's BS... taken this way, the only internal object is the object itself! How useless!

 

What is meant by inertial frame is a frame that maintains a constant velocity, right? Well that's just once again IGNORING the acceleration, which IS relative, because everything is!

[swansont]

But relativity says that one could claim to be accelerating themselves, or that everything else is accelerating and you are static. Every frame is equally valid.

 

Special Relativity says that inertial frames are equally valid. You can't tell who is moving at a constant velocity, but you can tell who is accelerating. I'm not making this up.

 

So, by your logic, if we chose the Sun as our coordinate system (the solar system, in other words), all of the planets are now external? Maybe you're just repeating what you've heard and learned, but this makes no sense to me. Relatively speaking, there's no such thing as "external" or "internal". That's BS... taken this way, the only internal object is the object itself! How useless!

 

It's not my logic, per se. There's actually a lot of use in being able to define systems (and coordinates) appropriate to the particular problem at hand.

 

If you want to understand some Newtonian dynamic, e.g. the behavior of the sun, defining the system to be the universe or solar system won't help, because then all of the forces are internal, and you have too many unknowns for your conservation of momentum to be of much use.

 

What is meant by inertial frame is a frame that maintains a constant velocity, right? Well that's just once again IGNORING the acceleration, which IS relative, because everything is!

 

No, it isn't.

 

If you're going to expound on relativity, it will be of great use if you would learn some of the fundamentals.

[galaxyblur]

Ok well, my point is (and tell me if you disagree, obviously):

 

-According to the Principle of Relativity, all laws of nature must be valid and nature must behave in the same way in ANY frame of reference.

-Since the Conservation of Momentum fails in Relativity (not even looking at Special or General), it cannot be a law of nature.

 

I'm not even TOUCHING Einsteinian Relativity... you took it there unnecessarily. C.o.Momentum fails long before that. If that law can't hold true in the simplest of examples when applied to Relativity, then its a relic of Newtonian Physics and cannot be used any further.

 

If you can explain how momentum is conserved at any point in time in my example, be my guest. I think we're arguing the same thing. You're saying that momentum is only conserved under a certain set of rules and from certain frames. That's absolutely the case. But if its not ALWAYS true, then its useless in Relativity.

[Cap'n Refsmmat]

That's because you're misinterpreting relativity.

[galaxyblur]

That's because you're misinterpreting relativity.

 

How so?

[Cap'n Refsmmat]

You state "According to the Principle of Relativity, all laws of nature must be valid and nature must behave in the same way in ANY frame of reference," when relativity states they must behave the same way in any inertial reference frame.

[galaxyblur]

You state "According to the Principle of Relativity, all laws of nature must be valid and nature must behave in the same way in ANY frame of reference," when relativity states they must behave the same way in any inertial reference frame.

 

Ok, so do we say inertial frame simply because our laws of nature fail in a non-inertial frame? I think there's something wrong with that. Here's what Wikipedia says, for what its worth:

 

"An inertial frame of reference, or inertial reference frame, is one in which Newton's first and second laws of motion are valid."

 

So by saying:

-The laws of nature only apply to inertial frames of reference.

 

we're basically saying:

-The laws of nature hold true in frames of reference in which the laws of nature can hold true.

 

Do a Google search for "inertial frame of reference" and you'll get similar explanations all over the place. The other type of explanation out there regurgitates "constant velocity". Well, shouldn't a fundamental law hold true all the time? If not, then we need another way to explain it in the "exceptional" cases, and thus, we need an idea that can bridge the two together.

[Sayonara]

Well, shouldn't a fundamental law hold true all the time?

Not in the sense you mean, no.

[galaxyblur]

Not in the sense you mean, no.

 

Please explain how a law of nature doesn't always have to be true. Not much of a law, now is it? Hardly "fundamental".

[Sayonara]

Well, things that it doesn't describe aren't required to behave in any particular way by that law (bearing in mind that a "law" is a specific description for something we observe to be consistently true).

 

So if a law pertains to inertial reference frames, it doesn't necessarily follow that it should have anything to say about any other kind of reference frames. Just like it has nothing to say about filofaxes, ice cream, or bungee jumps.

[galaxyblur]

Well, things that it doesn't describe aren't required to behave in any particular way by that law (bearing in mind that a "law" is a specific description for something we observe to be consistently true).

 

So if a law pertains to inertial reference frames, it doesn't necessarily follow that it should have anything to say about any other kind of reference frames. Just like it has nothing to say about filofaxes, ice cream, or bungee jumps.

 

I agree with you 100%. Which is why there has to be some deeper explanation. When you take Relativity in its truest sense (non-inertial, inertial, whatever), here's what gets thrown out the window:

-Conservation of Momentum

-Things "aquiring" and "transferring" energy, therefore...

-Conservation of Energy.

-You know what? Let's throw out this "Energy" thing all together. Fictitious.

 

Can you think of a case when energy cannot also be referred to as the relative velocity between two fields?

[Sayonara]

Gravitational potential energy.

[galaxyblur]

Gravitational potential energy.

 

If you do away with Energy, there needn't be any Potential or Kinetic. And isn't a velocity of zero still a velocity?

 

Potential Energy is completely unnecessary. Kind of like when they used to think Electricity was a fluid.

[Sayonara]

If you do away with Energy, there needn't be any Potential or Kinetic.

Backwards justification.

 

And isn't a velocity of zero still a velocity?

No. Velocity is a vector quantity - it has a directional component.

 

Potential Energy is completely unnecessary. Kind of like when they used to think Electricity was a fluid.

You know, if you have to break and discard the current framework to make whatever ideas you have workable, then you also need to replace all of its functions.

[swansont]

Are you really this ignorant of physics or are you being deliberately obtuse? From your use of the words, you don't know what a law is in science, in addition to your misunderstanding of relativity.

 

Many physicist and engineers find the concepts of energy and momentum, and their conservation under the appropriate conditions, to be useful. That you choose not to find them useful in no way dimishes it for the rest of us.

[galaxyblur]

No. Velocity is a vector quantity - it has a directional component.

 

Yes, and the velocity in any direction is therefore zero.

 

You know, if you have to break and discard the current framework to make whatever ideas you have workable, then you also need to replace all of its functions.

 

I understand that it would be a huge task to replace our current framework of energy. And I'm not saying that I'm even capable of doing so. But shouldn't we be moving forward, if we find that our current understanding does not account for all events in the universe? What physicist would tell you that we are 100% right about everything? Not one. It all has to change sooner or later.

[Sayonara]

Yes, and the velocity in any direction is therefore zero.

Velocity is defined as the rate of change of displacement, so by definition you can only have a non-zero velocity. The phrase "zero velocity" simply means that the item being observed has no velocity attributed to it, not that it has a velocity with the value zero.

 

In other words, "zero velocity" is a semantic construct, not a physical one.

 

 

I understand that it would be a huge task to replace our current framework of energy. And I'm not saying that I'm even capable of doing so. But shouldn't we be moving forward, if we find that our current understanding does not account for all events in the universe? What physicist would tell you that we are 100% right about everything? Not one. It all has to change sooner or later.

You don't have to be 100% right about everything in order to avoid randomly throwing out perfectly adequate bits of physics without replacing them.

 

If you have compelling reason to get rid of energy as a defunct concept, then explain it. Don't try to be mysterious or do the slow reveal - they work well in suspense movies and strip clubs but they are highly aggravating on science forums.

[galaxyblur]

Are you really this ignorant of physics or are you being deliberately obtuse? From your use of the words, you don't know what a law is in science, in addition to your misunderstanding of relativity.

 

Many physicist and engineers find the concepts of energy and momentum, and their conservation under the appropriate conditions, to be useful. That you choose not to find them useful in no way dimishes it for the rest of us.

 

Hey, it may be useful, and we may build theory upon theory. But I don't see what's so sacreligious about trying to think of things from a different angle. I stated, first thing, that this was somewhat in the realm of philosophy as well. Yes, I know what a law is, but my point was that our laws are not the true nature of things. Maybe that's an obvious point to make, but physics has built a house of cards that will not stand long.

 

You claim I misunderstand relativity, but I believe its been misunderstood and misused in modern theory. Just my two cents.

 

Yet still, no one has explained to me why an accelerating frame is considered "invalid" other than that "it breaks stuff". By that logic, our view from the Earth is an invalid one, and perhaps from the sun, the galaxy, who knows.

[Cap'n Refsmmat]

Our view from Earth is not invalid, it's just not equal to all other reference frames because it's accelerating.

[galaxyblur]

If you have compelling reason to get rid of energy as a defunct concept, then explain it. Don't try to be mysterious or do the slow reveal - they work well in suspense movies and strip clubs but they are highly aggravating on science forums.

 

Haha

 

I'm not intentionally being mysterious or any of that. I do not have an answer. All I was curious to know was, do you agree that this is possible, yet inexplicable within our current understanding?

[Sayonara]

Sorry I have forgotten what the "this" in the question was.

[galaxyblur]

Our view from Earth is not invalid, it's just not equal to all other reference frames because it's accelerating.

 

That's my whole point. The measurements we would take are not equal in all frames... such as, momentum.

[someguy]

your question is interesting. I agree that this is somewhat fundamental and i can't believe that einstein couldn't answer you appropriately i'm not sure if i really found the best explanation let me know what you guys think. but i know for certain that if you qualify the universe as infinite mass, for the sake of argument, i do not require an infinite amount of energy to move even though from my reference frame an infinite amount of mass is moved.... I think the answer may be like this.

 

If you look at the twin paradox, you could say that the spaceship was stationary and therefore when you arrive back on earth the people on earth should have aged much less than you since it was the earth that was moving in relation to you in the spaceship if we chose the spaceship as the reference frame and changed nothing else.

 

as your velocity increases your mass increases, energy is all that of which the world is made of, by adding velocity to an object your are changing the object. this independent of any frame of reference. when you add energy to a pool ball the pool ball is different. that's why the twin paradox can work because independently from any frame of reference the spaceship is moving closer to the speed of light, the spaceship acquired the extra energy used to propel itself faster through time, not the planet earth. in your pool ball experiment the 5 ball never changed state. it never acquired any extra energy. the cue ball transferred energy from itself to the 1 ball. this is a fact independent of any frame of reference. so nothing is really contradicted though it seems like it is. therefore you are confused because you can say that the energy of one ball caused two balls to move. but only one ball is ever moving and you can know this because if we assume that all the balls were of equal mass, when moving at equal speeds, then one ball in this case will always be more massive than the other two, and that's the one moving, regardless of your frame of reference. so then i think that your problem may be a Newtonian problem, that is in fact fixed by relativity, rather than a problem with relativity.

[galaxyblur]

You bring up some very valid points. I've often thought about the "moving the universe" problem and I'm glad you brought it up.

 

Back to energy, can we say that the amount of energy something has is relative? Of course it is, because velocity is relative. You cannot be independent of any frame of reference... you are always observing from one.

 

Let's imagine it is 1904, before Einstein's paper was published. How could you explain a solution to the problem? Special Relativity should not enter into this equation at all, because we are dealing with low-velocity, low-energy, low-mass objects. In fact, gravity's effect is negligible as well. By Einsteinian thought, you acquire energy, and therefore mass, moving in your car (at least from the road's perspective), but the mass gained is minuscule....

 

(this gives me an interesting thought: going back to attaining light-speed in a rocket, from your perspective, you never gain any energy and therefore mass. So why the explanation that light-speed is unattainable? That's for another time I suppose.)

 

Anyway, you are still looking at this from an absolute perspective. And all of this actually is beginning to feel even less intuitive than SR or GR or time dilation, which is quite a feat! I'm stumped for tonight perhaps.

 

Sorry I have forgotten what the "this" in the question was.

 

"this" being the 5-ball moving upon collision with the cue ball (from the 1-ball's perspective)

 

just read a couple of the stickies in this forum. Forgive me if I've committed a few atrocities. Won't happen again