Can you play left-handed in an orchestra?
Left-playing orchestra members did and do exist – even in professional symphony orchestras.
Since the old prejudice that left-handed orchestral playing is not possible primarily affects the string section, we will concentrate on them for now.
1. prejudice: "Left-handed players need too much space."
Wrong. Left-handed players need just as much space as right-handed players. Only possibly on the other side. This can be taken into account when setting up, so that there are usually no problems when right- and left-hand players play together (even when sharing a music stand).
For cellos, Walter Mengler 2010 states a space requirement "a few centimeters" higher because of the horizontal bowing. For violins, violas and double basses, this point does not apply due to the more vertical bow movement or the short bow. 
Our interviewed orchestra cellists confirm those "extra centimeters" and explain that an orchestra needs to first check how everyone is coping with the space in a narrow room or pit anyway – regardless of which hand they are bowing with.
Ludwig Quandt, (right-handed) principal cellist of the Berlin Philharmonic, explains in our interview: " Getting in the way of your fellow players with the bow happens anyway. I must have hit someone with the frog in the scroll at least a dozen times."
-> Whether in school orchestras, amateur orchestras or professional orchestras: Wherever left-hand playing is attempted, solutions are found.
2. prejudice: "It looks messy when not all bows move to the same direction and it confuses the colleagues."
Walter Mengler also got this right to the point:
"An audience quickly gets used to the slightly different look, just as the enjoyment of a Strauss score is not marred by the fact that the violins are often split six ways and repeatedly bow against each other. Mahler's Adagietto from the 5th Symphony loses none of its emotion, either, as the cellists play two different parts on each stand, almost permanently bowing against each other to do so."
From the experience of left-handed orchestral musicians, whom we have interviewed on the subject, it also turns out that the audience reacts with curiosity and delight rather than rejection and irritation - if they notice the other direction of playing in the midst of a large orchestra at all.
The orchestra colleagues also quickly get used to it, as our interviews unanimously reveal. After all, the joint playing is more a question of energy than of absolute bowing direction: "An up bow just feels completely different from a down bow in terms of energy. So, when I play, I feel in harmony with all the string players, regardless of left or right," reports cellist Laila Kirchner, who plays both right- and left-handed.
And last but not least: Considering how it is supposed to disturb an allegedly homogeneous appearance, it takes an astonishingly long time to spot the left-handed playing person in orchestra photos or videos.
3. prejudice: "Orchestras don't take in lefties." – or: The hen and the egg
Many music instructors claim this as the reason why they do not let a student play left-handed, even if they realize the child would probably find it easier to do so. They do not want to spoil the student's potential future as a professional musician right from the start.
In our opinion, this is a thinking error in several respects:
Firstly, playing left-handed in any ensemble is not a problem (see above) and also occurs in professional orchestras (see below).
Secondly, the fact that left-handed orchestra members have only appeared in homeopathic doses so far is not due to the fact that applications by left-handed players are rejected by the orchestras straight away. Rather, the orchestras are hardly ever confronted with left-handed applications at the moment, precisely because so few children and young people learn to play their instrument left-handed – out of concern on the part of the teachers that they would not be allowed to play in an orchestra that way... We are going around in circles.
Thirdly, an overwhelming proportion of children who start music lessons will not think about making a career out of it later on anyway. And of the very small number who do, only a tiny fraction will actually try out for an orchestra position at some point. There are so many other possibilities to make a living with music... And from the tiny part that comes to the audition (from the very small part that wants to make music professionally) not everyone gets an orchestra position anyway – no matter if they play right- or left-handed.
It therefore makes absolutely no sense to make the playing direction of a beginner child dependent solely on presumed "prerequisites" for a hypothetical orchestra position. Rather, our goal should be to develop a solid technique, expressive tonal possibilities and a healthy posture in order to spark the joy of making music in the long term.
Some left-handed people do not experience problems on the conventional right-handed instrument. They feel comfortable with it and sometimes play professionally at a very high level. But for many others it is a handicap not to be able to produce and shape the sound with their strong hand. 
Many children cannot cope with playing against their left-handedness: They don't progress, feel uncomfortable at the instrument and give up in frustration after a more or less short time. This can always have other reasons too, of course, but a bow in their "right" hand can work wonders... ;)
To sacrifice the music-making joy of these left-handed children (who often take the bow in their left hand on their own initiative) to a false prejudice is absolutely unnecessary.
We should move towards letting children make music according to their lateral disposition – for more joy in playing, musical success, health and well-being for all involved.
As a result, there will be more left-handed applications for orchestra positions in the future. But who actually says that they do not have the same chances as right-handed applicants?
Ludwig Quandt, principal cellist of the Berlin Philharmonic, is already certain: "Our orchestra hires according to quality only. If a left-handed player comes in, plays left-handed and sweeps all the others off the court, then he or she will come into the orchestra and a solution will be found. We have no statutes that exclude left-handed players."
List of left-handed playing musicians in professional orchestras
Orchestra in Münster, later Krefeld and Marburg  (D): Richard Barth, violinist and concertmaster from around 1867
Radion Sinfoniaorkesteri (Finnish Radio Symphony Orchestra): Paavo Berglund, violinist (1st) from 1949 to 1958 
Buffalo Philharmonic Orchestra (US): Rivka Mandelkern, violinist (1st) from around 1954 to after 1980
Südfunk Symphony Orchestra (today: SWR Symphony Orchestra) (D): violist[?] around 1970
Orchestra Heidelberg (D): Jürgen Kussmaul, principal violist
Gürzenich Orchestra Cologne (D): Jürgen Kussmaul, principal violist
Municipal (today: Philharmonic) Orchestra Bremerhaven (D): Dieter Görnandt, solo violist
DR SymfoniOrkestret (Danish National Symphony Orchestra): Nils Sylvest, cellist from 1980
The City of Birmingham Symphony Orchestra (UK): Margaret Artus, violist from 1984 to before 1998 
Loh Orchestra Sondershausen (D): Hans-Ludwig Becker, solo cellist from 1991 to 1998
Bad Reichenhall Philharmonic (Germany): Franz Slaboch, violinist (2nd) since 1985
Opera Ballet Vlaanderen (Belgium): Hans-Ludwig Becker, second solo cellist since 1998
Orquesta Sinfónica de Salta (Argentina): Gerardo Solórzano, violinist since about 2002
Les Siècles (France): Martial Gauthier, leader of the second violins since 2005
Niagara Symphony Orchestra (Canada): Filip Stasiak, double bass player
Orquesta Sinfónica Nacional (Mexico): Abner Jairo Ortiz García, cellist since 2019
 Walter Mengler: Musizieren mit links (= Making music with the left). Mainz 2010.
 This is explained in detail in the relevant literature (German) and described in numerous interviews and blog posts.
 according to Wikipedia
 Many thanks to Richard Bratby for the details!