Relativity - Oh dear, here we go again!

[sol invictus]

Relativity does however contain a "let's pretend" part*.

I don't agree. It's not a question of "let's pretend" - it's "let's assume". So long as the assumption is useful (i.e. the theory based on it makes useful predictions and doesn't conflict with experiment) we retain it. The minute that fails, we drop it.

But there is neither need nor room for pretending anything.

 

[wackyvorlon]

I have to wonder, am I the only person for whom the twins paradox makes complete sense?

 

[Dorfl]

I have to wonder, am I the only person for whom the twins paradox makes complete sense?

I think I understand it. I mean, if you draw the world lines it seems kind of obvious what's happening.

 

[Dancing David]

Ynot, you are attacking a straw position.

there are many factots in the theory of 'relativity'.

the largest one (I think) is the invariant speed of light. It will be measured to be c to all observers.

Now I just can't seem to parse what you are saying here:

A thing isn’t stationary relative to itself as a thing can’t be relative to itself. A thing IS itself. A thing is always constantly moving relative to the previous positions of itself.

Could you elaborate your thinking behenid this statement.

Motion is always measured in relation to some 'mark or 'frame of reference'.

So I do not understabd your point.

A thing in and of itself is a 'mark' or a 'frame of reference', so it can be viewed as at rest or in motion in refernce to ther 'marks' or 'frames of reference'.

What is your point?

 

[Dancing David]

I have to wonder, am I the only person for whom the twins paradox makes complete sense?

It makes sense to me, as I have read science fiction that involved the concept since I was a wee lad.

My favorite being Tau Zero by P. Anderson (I think)
http://www.amazon.com/Tau-Zero-Poul-Anderson/dp/0425050777

Although the short story A World Out of Time by Niven was very cool as well
http://en.wikipedia.org/wiki/A_World_Out_of_Time

Although the
Last Starship from Earth by Boyd gets into what if you could go faster than C and go back in time
http://www.amazon.com/Last-Starship-Earth-John-Boyd/dp/0140048758

But Time for the Stars by Heinlein was the first that I read and a classic as it involves the twins themselves.
http://en.wikipedia.org/wiki/Time_for_the_Stars

 

[Ziggurat]

the largest one (I think) is the invariant speed of light. It will be measured to be c to all observers.

It's c for all inertial observers in special relativity. We do need to make the distinction explicit, because some people take the Sagnac effect as evidence against relativity, since c is not constant for non-inertial observers.

 

[ynot]

Seems even those that “understand” Relativity aren't quite in agreement.

As I understand it Relativity essentially says that rather than being a single absolute reality the Universe is made up of an infinite number of relative realities that are each absolute realities in their own right. Is this correct?

 

[Dorfl]

As I understand it Relativity essentially says that rather than being a single absolute reality the Universe is made up of an infinite number of relative realities that are each absolute realities in their own right. Is this correct?

I am not sure what you mean by "relative absolute realities". Could you please clarify?

 

[Myriad]

Seems even those that “understand” Relativity aren't quite in agreement.

As I understand it Relativity essentially says that rather than being a single absolute reality the Universe is made up of an infinite number of relative realities that are each absolute realities in their own right. Is this correct?

No.

There is an infinite number of different reference frames from which any events can be observed and evaluated, but these are not different realities, any more than the infinite number of different possible camera angles for photographs of the Brooklyn Bridge are actually an infinite number of different bridges.

Respectfully,
Myriad

 

[ynot]

I am not sure what you mean by "relative absolute realities". Could you please clarify?

I can try but I can’t guarantee it will clarify - Take the “twins” scenario. To begin with the twins share the same relative absolute reality and both age at the same rate. One twin then “travels” and experiences a different relative absolute reality than the “stationary” twin and ages more slowly. When the twins get back together they share the same relative absolute reality again but not the same age because the “travelling” twin experienced a period of a different relative absolute reality where time passed relatively slower.

ETA - relative absolute reality = inertial frame

 

[ynot]

No.

There is an infinite number of different reference frames from which any events can be observed and evaluated, but these are not different realities, any more than the infinite number of different possible camera angles for photographs of the Brooklyn Bridge are actually an infinite number of different bridges.

Respectfully,
Myriad

Angles of perception in the same “relative absolute reality“ (inertial frame) is not the same thing as Relativity claiming that time passes at relatively different rates in different “relative absolute realities” (inertial frames).

 

[Dorfl]

I can try but I can’t guarantee it will clarify - Take the “twins” scenario. To begin with the twins share the same relative absolute reality and both age at the same rate. One twin then “travels” and experiences a different relative absolute reality than the “stationary” twin and ages more slowly. When the twins get back together they share the same relative absolute reality again but not the same age because the “travelling” twin experienced a period of a different relative absolute reality where time passed relatively slower.

I might understand, but it seems like a very confusing and non-standard terminology to use. Since the term "relative absolute" is an oxymoron, would it not be clearer to simply say "relative"? It seems that the term—as you use it—has a meaning which is closer to the meaning of the word "relative" than any other term, if we use the standard meanings of words.

Either way, I do not see why you are talking about the twins as "experiencing different realities". They are taking different routes travelling through space-time, which leads to them passing over different distances through space and time. Calling this having different realities seems like saying that a person walking from Madrid to Tunis and another flying have different realities, because they traverse different distances and take different times getting there.

I'm not sure how intelligible any of what I just said was, though. It is past bedtime, here.

 

[ynot]

I might understand, but it seems like a very confusing and non-standard terminology to use. Since the term "relative absolute" is an oxymoron, would it not be clearer to simply say "relative"? It seems that the term—as you use it—has a meaning which is closer to the meaning of the word "relative" than any other term, if we use the standard meanings of words.

Either way, I do not see why you are talking about the twins as "experiencing different realities". They are taking different routes travelling through space-time, which leads to them passing over different distances through space and time. Calling this having different realities seems like saying that a person walking from Madrid to Tunis and another flying have different realities, because they traverse different distances and take different times getting there.

I'm not sure how intelligible any of what I just said was, though. It is past bedtime, here.

According to Relativity the twins experience different realities of time.

 

[Ziggurat]

According to Relativity the twins experience different realities of time.

They experience different proper times. This term has a specific meaning, and it is exactly equivalent to saying that people who take different paths to the same location will have traveled different distances. "Realities of time" is a meaningless phrase.

 

[BillyJoe]

ynot,

You need to drop your term "relative absolute reality". It makes no sense to anyone else here. In fact, "relative" is the opposite of "absolute" in this context. In short, relativity is the idea that there are no absolutes. To say that spacetime is absolute is to say there is some point from which everything else has to be measured. On the other hand, relativity gives equal standing to all points in spacetime. No point is spacetime is favoured above any other point.

As for the "reality" part, everyone can agree on the mathematics at every point in spacetime, so it's all part of the same reality. To say A moves towards B in B's frame of reference, is the same as saying that B moves towards A in A's frame of reference. It describes the same reality from different points of view - just like the photographs shot from different angles describes the same bridge.

BillyJoe

 

[Ziggurat]

ynot,

You need to drop your term "relative absolute reality". It makes no sense to anyone else here. In fact, "relative" is the opposite of "absolute" in this context.

This is completely correct.

In short, relativity is the idea that there are no absolutes.

Actually, no. Velocity is purely relative, but I think it's important, especially in this context, to recognize that there are absolutes in relativity. Such things are usually referred to as "invariant". Proper time is invariant. Proper length is invariant. The most meaningful definition of mass is invariant. We can treat these things as absolutes. They are not relative to anything, and all observers will agree on them.

 

[ynot]

You seem to think that "X is not stationary in an absolute sense" means the same thing as "X is moving in an absolute sense". Those two statements are very different.

If it’s not an either/or choice what is the third alternative?

 

[ynot]

I agree that “relative absolute” is a nonsense/oxymoron. I guess I used the term to highlight that Relativity (as I understand it) also seems to be a nonsense/oxymoron.

I also guess that I often use made-up phrases to replace the conventional ones in an attempt to express the same thing differently so the thing might be considered from a fresh perspective. From a sceptical perspective Relativity seems to use a lot of terms that are “user friendly”. I don’t think this is any form of conscious conspiracy but perhaps there is an ongoing subconscious confirmation bias. It’s most likely however that I simply don’t fully understand the language and how it’s correctly applied to reality.

 

[ynot]

ynot,

As for the "reality" part, everyone can agree on the mathematics at every point in spacetime, so it's all part of the same reality. To say A moves towards B in B's frame of reference, is the same as saying that B moves towards A in A's frame of reference. It describes the same reality from different points of view - just like the photographs shot from different angles describes the same bridge.

BillyJoe

So why don’t the twins time dilate relative to each other at the same rate?

 

[Ziggurat]

So why don’t the twins time dilate relative to each other at the same rate?

They do, as long as they are both inertial. But the traveling twin isn't always inertial.