Why is relativity so hard to learn?[1]

[BurtJordaan]

Whose clock are you using to say Alice's age when she is back with Bob?

Her own clock, what else? Just recall that Alice progressed less "inertial time" than Bob, or like Dave_O said, she took a "shortcut" through Bob's time. But do not take that too literally - she has covered exactly as much spacetime distance as Bob has, just a bit more space and a bit less time.

[vivian maxine]

Thank you, Bert. And, as to my first question, in the real scientific world, Alice is actually still Bob's age? Forgive me if I seem to be beating a dead horse but I sometimes have gotten a feeling that some are treating "relativity" as "reality". I just want to hear someone say it really is only relative between two observers - Bob and Alice with their respective clocks.

[BurtJordaan]

No, she will actually be younger than her twin Bob after such a trip. This is 'real' relativity, not of the "each thinks the other is aging slower" variety. Alice's acceleration has put her in a different spacetime structure, where she ages less than Bob, between two events that they both share (departure and arrival).

[Dave_Oblad]

Hi All,

Sorry, I removed myself from commenting on this thread as I disagree with the way SR treats Time. Don't get me wrong, SR had accomplished much, but the interpretation of Time has obvious logic issues. But I didn't want to derail a thread intended to teach Relativity, so pretend I'm not here.

In SR discussions it's not unusual to grant Players "Far Sight". The ability to watch each others clocks instantly and without Doppler considerations. As such: If Alice and Bob were Twins and she took off on a long Relativistic Velocity journey and returned eventually to Bob, He would have aged more than Alice. With Far Sight, Bob would no doubt see Alice's clock as Running slower than His. And She would watch His Clock running faster than Hers.

This is the only way that an aging discrepancy can be observed and match the predicted outcome. I accept that all velocities through Space-Time alter the Geometry of Moving Matter such that the closer one comes to Light Speed then the slower they Age (and clocks slow) as a real process in the physical mechanics of Matter-Energy.

This I believe is the real reason Relativity is hard to learn.. it's not logically consistent and a lot of people figure that out fairly easily.

But again, I don't want to derail this thread, so I'll remain silent on the subject of "Time" unless asked by Jorrie to post my issues here.

Best wishes,
Dave :^)

[BurtJordaan]

Hi Dave.

Don't get me wrong, SR had accomplished much, but the interpretation of Time has obvious logic issues.

I do not quite understand what you mean by "interpretation of Time", but SR has no "interpretation of time"; it simply defines it (via the constancy of c and the resulting definition of simultaneity) in a logical way and then use that in a completely consistent manner. To me, it is a mystery why people have such difficulties to understand it.

Suppose you have never read the nonsensical notion of "moving clocks slow down" and just about spacetime structure and the fact that clocks (actually all objects) can have different paths through this structure and hence record different elapsed times between events; would that have made it easier for you to interpret?

In SR discussions it's not unusual to grant Players "Far Sight". The ability to watch each others clocks instantly and without Doppler considerations.

BTW, this "Far Sight" is just a network of clocks synchronized for each inertial frame of reference. Players don't have "far sight", but inertial frames have it through their set of synchronized observers. The space-propertime view that I explained here makes use of this fact, although you may have noticed that I did not talk about simultaneity or time dilation here - just spacetime paths and proper time, the latter as read off clocks at close distance.

IMO, that's where the key to SR/GR lurks, with the other (more esoteric effects) just red herrings...