A space travelers mass

[asprung]

The tree may look higher but it is not higher.We seem to be talking about how things look to diffrent observers not how they are. There would be a contradiction between a flat spaceman and one that has not become flat.

[Cap'n Refsmmat]

The tree analogy doesn't really work because the tree has an easily measurable height.

 

There may be a contradiction in what you see, but how do you verify which observer is correct?

[Klaynos]

The tree may look higher but it is not higher.We seem to be talking about how things look to diffrent observers not how they are. There would be a contradiction between a flat spaceman and one that has not become flat.

 

Consider 2 spacemen A and B.

 

They are moving relative to each other at a constant velocity v close to c.

 

B looks in a mirror and sees himself fine, and looks at A and sees him 'flat'.

 

Also:

 

A looks in a mirror and sees himself fine, and looks at B and sees him 'flat'.

 

Now consider a third space traveller C that is travelling relative to B at velocity u so that u and v are both in the same direction. He would see both A and B to be elongated and they would see him to be elongated.

 

None of them are wrong.

[asprung]

They would not be wrong as to how they see him, but they would be as to how he is in his own frame which should be controlling. Thats how he starts out and without actual phisical distortion thats how he should remain.

[iNow]

They would not be wrong as to how they see him, but they would be as to how he is in his own frame which should be controlling. Thats how he starts out and without actual phisical distortion thats how he should remain.

 

But this implies that his own frame is somehow more relevant than theirs.

It's not.

No frame of reference is special, and your comment only works if his frame of reference is arbitrarily made special or absolute.

 

There are no absolute or privileged frames of reference.

[asprung]

Thats the way he starts and thats the way he should end up unless altered.

[iNow]

Thats the way he starts and thats the way he should end up unless altered.

 

And he does. What makes you think he would not "end up" the same as when he started (leaving out, for the moment, any aging effects)?

[asprung]

Thats the whole point. He hasnt changed but only appears to from other time frames.

[Cap'n Refsmmat]

But we have no way of determining which frame, while he's moving, is the "right" one.

[iNow]

Thats the whole point. He hasnt changed but only appears to from other time frames.

 

So, you and I are standing face to face, in front of each other.

 

Someone near us says, "Both of you, point north."

 

I point to the left.

You point to the right.

 

Which one of us is "right?" The question doesn't make sense, since we both are. It's just that, to me, north is on the left, and to you, north is on the right.

 

It's pretty much the same way with time and length. Our "reference frames" are different, but neither one of us is more correct than the other.

 

 

NOTE: This is just an anology, as the concept of "north" implies absolute frame. It was used only to assist in the visual. As has been repeatedly stated, there are no absolute frames.

[thedarkshade]

The tree analogy doesn't really work because the tree has an easily measurable height.

Ok ok I agree, but I couldn't think of anything simpler, and I did put "rough" before analogy.

[swansont]

Thats the whole point. He hasnt changed but only appears to from other time frames.

 

Changed is perhaps the wrong word. What is seen/measured is different in different frames. My motion doesn't alter an object, but what I see is different in different frames, and I have no way of saying that one frame is the "right frame" and that's the "real appearance" of the object.

 

So with a meter stick, I can't say that it is "really" one meter long because I can't tell if I'm moving or at rest. It's only a meter long in a particular frame of reference — the length is not an inherent property of the stick. In one frame it's 1.00 meter, in another frame it's 0.99 meters, and in yet another, it's 0.90 meters. Nothing physical has happened to the stick, but I can't say how long the stick is, only how long it is in a particular frame of reference.

[asprung]

Does it follow that nothing physical has happend to the spaceman. He only has different appearences from different frames of reference. A physical change would be an event the occurence of which could only be viewed "now" by all [though there may be a disagreement as to its time] and I could not see how he could physical change and not change in the same "now"