Register

Adv. Query

Q&A (4868)

Reviews (203)

Open problems (47)
Meta (439)

Site Statistics

205 submissions , 163 unreviewed
5,082 questions , 2,232 unanswered
5,353 answers , 22,789 comments
1,470 users with positive rep
820 active unimported users
More ...

Does an apple "falling" from a tree move only in the time direction in curved spacetime?

1357 views

Does it appear to a distant observer that the distance between the earth and the apple is decreasing as they move along their geodesics but only in the time direction , and in reality neither the earth or the apple move through space?

Closed as per community consensus as the post is not graduate-level

asked Nov 25, 2018 in Closed Questions by anonymous [ no revision ]
recategorized Nov 27, 2018 by Dilaton

not graduate+ level. Users with 500+ reputation may vote here to close.

PhysicsOverflow is a site for advanced physics. Please ask elementary
question in other online platforms that value such questions.

commented Nov 26, 2018 by Arnold Neumaier (15,787 points) [ revision history ]

I bet you can't answer it correctly..

commented Nov 26, 2018 by anonymous [ no revision ]

Your statement reveals elementary problems in understanding the notions involved. Motion ''in time only'' depends on the coordinate system used, and would imply in this coordinate system that the spatial distance does not change, which is obviously wrong.

commented Nov 27, 2018 by Arnold Neumaier (15,787 points) [ revision history ]

Your comment on this question:

To answer, leave an answer instead. Comments are usually for non-answers.
To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL.
To alert a user, please use the "@" command and remove spaces from the username, example, the user "John Doe" should be pinged as "@JohnDoe", while the user "Johndoe" should be pinged as "@Johndoe". The post author is always automatically pinged (unless you are the post author).
Please consult the FAQ for as to how to format your post.

Live preview (may slow down editor) Preview

Your name to display (optional):

Email me at this address if a comment is added after mine:

Privacy: Your email address will only be used for sending these notifications.

Anti-spam verification:

If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:
p$\hbar$ysi$\varnothing$sOverflow
Then drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds).

Please complete the anti-spam verification

1 Answer

In GR "moving through space" is implied; otherwise the notion of space would be useless. You mistake a "free motion" in space (=along geodesics) for "no motion at all".

answered Nov 27, 2018 by Vladimir Kalitvianski (102 points) [ no revision ]

Your comment on this answer:

To answer, leave an answer instead. Comments are usually for non-answers.
To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL.
To alert a user, please use the "@" command and remove spaces from the username, example, the user "John Doe" should be pinged as "@JohnDoe", while the user "Johndoe" should be pinged as "@Johndoe". The post author is always automatically pinged (unless you are the post author).
Please consult the FAQ for as to how to format your post.

Live preview (may slow down editor) Preview

Your name to display (optional):

Email me at this address if a comment is added after mine:

Privacy: Your email address will only be used for sending these notifications.

Anti-spam verification:

[captcha placeholder]

Please complete the anti-spam verification

user contributions licensed under cc by-sa 3.0 with attribution required

Your rights

...