Why do the soloists go to the concertmaster when the string breaks
Why dont they swap the violin with the second violinist
I think the concertmaster is more important than other members in the violin section
They're the closest, so the change happens most quickly?
The concertmaster is immediately at hand, should be paying attention, and probably is playing a decent violin.
I recall a radio broadcast of Heifetz with the NBC Symphony Orchestra (I think - that or the Bell Telephone Hour) when they reported at the end that a string had broken and he exchanged fiddles with the CM. This had to be at least 70 years ago - unfortunately on radio you don't see this happen.
They have nicer instruments than 2nd chair. I kid.
Well Jeff, you are onto something... Getting paid more than the rest of the minions, chances are that the 2nd best fiddle on stage is concert-master's! There is also a belief that excellent musicians keep looking for extraordinary instruments....
As noted above: (1) proximity and (2) the high likelihood that the concertmaster has the second best violin on stage, after the soloist.
Is the CM required to let the soloist play theirs if they break a string? Why not just have a backup ready to go like pro guitarists do?
You don't have time to change a string unless there's a long tutti.
Violins are much more expensive, especially violins of the quality that professionals are likely to use. A good violin does not leave the violinist's hands when it is out of its case. And strings break rarely enough that, if you put a backup violin on a stand on stage as guitarists do, the risk of damage to the instrument outweighs the small likelihood of needing to use the backup.
Some soloists might have a backup instrument backstage, but there's no time to go grab it except possibly in a break between movements.
Lydia, I have an ancient memory of being a cellist in the orchestra for Mahler 4 (I think it was). During a rehearsal the CM made a fuss because there was no way he was going to tune one of his very good violins up a half-tone for that solo. What happened in the end was that his wife, a music teacher at a local school, borrowed one of the better VSOs from the music department and strung it up with steel strings. It did the job fine.
I recently lent my violin and bow to a middle-school soloist during rehearsals for a concerto that the kid was performing with my community orchestra, after concluding that the projection challenges were primarily an equipment problem rather than primarily a technical issue.