Is the Pen on My Desk a Geodesic and Is My Room an Inertial Frame?

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Discussion Overview

The discussion revolves around whether a pen on a desk can be considered to describe a geodesic and whether a room can be classified as an inertial frame. The scope includes conceptual exploration of geodesics in general relativity and the characteristics of inertial frames in the context of special relativity.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that the pen does not describe a geodesic because it is not in free fall and believes the room is a good approximation of an inertial frame.
  • Another participant counters that if the desk were absent, the pen would describe a geodesic for a brief period, implying that the presence of the desk affects the situation.
  • A third participant proposes that the room could be viewed as an approximation of a frame undergoing constant 1G acceleration, relating it to concepts in special relativity.
  • A later reply reiterates that an object describes a geodesic only when it is in free fall, acknowledging the previous contributions.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which the pen describes a geodesic and the nature of the room as an inertial frame, indicating that multiple competing views remain without a consensus.

Contextual Notes

The discussion highlights assumptions about free fall and inertial frames, as well as the implications of external forces like the desk on the pen's motion. There are unresolved nuances regarding the definitions of geodesics and inertial frames in different contexts.

wpoely
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Hi,

I was wondering: I'm sitting at my desk and on my desk lies a pen. Does the pen describe a geodesic? And is the room I'm sitting in an inertial frame?

I think the pen doesn't describe a geodesic because it's not in free fall and i think my room is a good approximation of an inertial frame for things that happen in my room.

Am i right? Thanks!
 
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No. If the desk wasn't there, then for a few seconds the pen would describe a geodesic. Similarly, your room is no better inertial frame than an elevator.
 
Your room would be a good approximation for the frame of a room undergoing constant 1G acceleration through space in special relativity.
 
So, in practice, only when an object is in free fall, we know it describes a geodesic.

Thanks for the answers!
 

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