J.C.MacSwell

Try this thought experiment.[/b']?

No question in my mind that in this thought experiment the clock that went further will be "younger", primarily due to the due to the SR effect. The GR effects could be symmetrical.

I do wonder: What is the "BEST" experimental evidence to support this. All evidence I have seen has a major GR component chomping into any margin of error.

It is impossible to get any results on SR without being exposed to some GR effects. The best we can hope for is to make them symmetrical (with respect to what though, time or distance etc.) or to factor them out based on theory.

It is also impossible to make them perfectly symmetrical or you would be duplicating the same test. No comparison could be made.

Apologies if any of that does not make sense.

You are adding mass in these scenarios' date=' but not rest mass. AFAIK rest mass of an atom assumes ground state. Excitaton at some level includes KE of particles, and as the bouncing rubber balls show, that's becoming absurd by the time you reach macroscopic systems.

 

Mass is a property of matter, but is not a synonym for matter. Matter is something that has mass and takes up space. Severian gave a more technical definition here.

 

Whether mass represents how much matter you have, I think is more to do with semantics. Is it energy or is it number of particles? One needs to define the problem more clearly, and declare which metric one is to use to measure it.

Thank-you. I was surprised that Sevarians particle physics description of matter excluded the gluon.

The point about not adding to the constituents' rest mass is why I would argue that you haven't created any matter. To make an energy argument, you would also have to say that a particle in motion constitutes more matter than a particle at rest.

But doesn't exciting an atom add rest mass to the atom, though (I think, not sure- I see it as kinetic?) not the electron?

By this definition (which I now suspect is wrong but was my original thought) I would have created additional matter.

Using the broadest possible definition if you had a big hollow sphere in outer space, filled with rubber balls bouncing around would their kinetic energy add to the "rest mass" of the big hollow sphere/system? I think it would be equivalent (add to it's inertia etc.) would it not? Obviously a stretch to call "that" additional matter.

What definition are you using? I don't think anyone actually mentioned a definition in this thread.

I was using, "energy of rest mass" as constituting matter, but I now suspect this is incorrect. An excitation of an atom would add to it's rest mass, would it not? Any thoughts?

On the same subject would the heat energy of a body add to it's rest mass? I would say yes (even though it does not add to the rest mass of the constituent atoms) but I would not think of this as matter so I am obviously unsure of where the line is drawn.

I think (now) matter is supposed to have some degree of "permanence" under normal conditions, so this may be too broad a definition that I was using. (even though matter created in some accelerator experiments is far from "somewhat permanent under normal conditions").

I would like to know where the lines are drawn (and more interestingly "why")

What if you had two cats in the box, one male and one female. After, say, 10 minutes a decay device will trigger one of them dead in a way that won't effect the other. (Say it triggers a cyanide capsule to rupture in the stomach).

So you have a live/dead cat and another live/dead cat. Can they interfere with each other?

Assume there is enough food and water in the box/system and half the box was isolated/compartmented so the cats can't get to it because of a trap door than wasn't (quite) big enough.

After a year the trap door is sealed and the isolation/compartment is saved and the remaining half is jettisoned into a black hole.

When the isolation/compartment is opened could it contain any kittens?

What matter exists that didn't exist before?

More energy is bound (somewhat) in the atom. The rest mass of the atom has increased.(?)

Does this not represent an increase in matter? Or am I getting the definition wrong? (I suspect I may be))

If a photon is absorbed by an atom bumping up an electron isn't that an increase of matter.(and therefore creation/transformation of energy into matter)

T

 

So that begs the question then' date=' [i']"What is the real reason why a spaceship can't accelerate to light speed?"[/i] The reason is because of the limitations imposed by relativity's Addition of Velocities formula. Let's say that you, a stationary observer, see the craft going 1000 MPH slower than lightspeed, and then it accelerates. The pilot of the craft might discern that his recent engine thrust boosted his speed by 5000 MPH (confirmed by his observation of something he left behind, eg. a sister ship). But to you, when the speed 5000 is added to the speed (c-1000), the sum does not surpass c. You have to use the velocity addition formula, (u+v)/(1+(uv/c^2)).

So it's Einstein's fault? Nobody blamed Newton when they fell down.

What do you mean. What is a rest[/b'] frame? Please don't say that it's a frame at rest!

Isn't it a non-accelerating frame?

But how can you distinguish them? You can't - every physical observable that both Bob and Bill can measure will give the same result (assuming they are in a box' date=' or a lift or somesuch) so you cannot distinguish which one is in a gravitational field and which one is being 'slowed down'. Therefore there can be no difference in age.

 

[/quote']

 

 

Let's have the twins meet in outer space, Bob at rest and Bill 1/2 light speed with respect to Bob and they synchronize their watches on the "fly by". Both are then blindfolded. Bob "stays put" and feels nothing. Bill gets deflected around a series of gravitational objects without getting captured in their orbits until he again meets Bob again and they again check their watches on the second "fly by". Bill has felt nothing except possibly some slight tidal effects.

 

Would you say their watches still agree?

surely then the conversion of the entire ship into Energy would be required then?

and it would have to be a VERY efficient conversion leaving even the smallest of particle(s) massless' date=' and thus rendering the excersize futile, and Jakari point Valid?[/quote']

 

I think this is basically correct if you mean in order to "get to" light speed.

 

Lightsword was correct, I think, for the local frame of reference. He could still accelerate "normally". From your reference point this "normal" acceleration would seem futile as he would be using an awful lot of energy for a miniscule acceleration. But from his point of view this miniscule acceleration and the energy expended would be business as usual.

 

Remember that he changed his reference frame as he approached light speed so that he would be unaware of any mass (whatever mass is) increase. Having changed his reference frame he is also no closer to the speed of light. So he can happily accelerate away in his local reference frame even though it's perfectly obvious to you that he's just "spinning his wheels"

I agree with pretty much everything that Martin (and JaKiri) said. I only have one clarifying comment:

 

The twin paradox is normally formulated assuming Bob is at rest in a frame with no gravity - so he is feeling no force' date=' while Bill feels the acceleration 'force' when he turns round. If Bob were on Earth the whole time and Bill maintained an acceleration/decelaration of 1g the entire time of his travel, their clocks at the end would show the same time - they would have aged the same amount because one could not tell their frames apart from the forces they feel.[/quote']

 

Is this correct?

 

Bob is in a constant situation. Let's say you doubled the duration of the test (Bob's time) he would be twice as old. Bill would be closer to light speed (Bob's perspective) through the "middle half" of the longer test than in the first and last quarters (the "other half" which is identical to the original test) of the longer test. So for Bill the "middle half" would be of less duration than the "other half" whereas for Bob it would be the same duration.

 

Bob would think the test doubled where Bill would think it increased somewhat but not doubled.

 

Thoughts?