Q:

Was Luke, the author of the Gospel and Acts, a slave?

"It is possible that Paul’s “relative” Lucius is Luke, the author of
  the Gospel and the Acts of the Apostles. On his second missionary
  journey, Paul may have gone to Troas (where Luke lived—or at least
  where he joined Paul) because he knew a relative he could stay with
  there (Acts 16:8, 11)." -
  http://www.christianitytoday.com/ch/1995/issue47/4702.html

I know a related question is this: Who was Luke in the Bible? But I find the answer lacking. I recently heard teaching on slavery in the New Testament by Michael Card, and he presented Luke as a slave, and physicians in general as slaves in the time of the New Testament. 

The 'doctors' in ancient Rome were not nearly as highly regarded as
  the doctors in Greece. The profession itself, outside of the legions,
  was considered a low social position, fit for slaves, freedmen and
  non-latin citizens, mainly Greeks. unrv.com

He also taught that slaves in that time were named one of two way, 1) by the master's desired characteristic for the slave (the most common slave name, philokurios - loving of the master, and Philemon - dear one), or 2) by a nickname of the master (i.e. Michael would name his slave Mike).
Paul mentions a relative, Lucius. Lucius would name his slave Luke. As a physician, he would have been given to Paul to care for his ailment, (or thorn?). That would explain why Luke traveled so extensively with Paul. 
Michael Card does have a book on both slavery and Luke, and I will be getting to those, but how come I've never heard this before? Is there substantial evidence pointing to a definitive yes or no?

A:

Michael Card's hypothesis is interesting, and certainly not outside the realm of possibility.  It is quite true that skilled Greeks were enslaved and brought to Italy during times of conquest and revolt, and perhaps even during times of peace between Greece and Rome, such as was the case when Luke was living.  But it seems to me that Card's main argument needs evidence to support it.  He claims that (1) Luke is a hypocorism based on the name Lucius; and (2) slaves were commonly named according to hypocirisms.  Both of these claims are plausible---but plausible isn't good enough.  He needs to give some evidence that this was actually the case.
Unfortunately, even then, the case wouldn't be made.  Card himself understands this, when he writes:  "I admit that this idea is quite a stretch, and my scholarly friends have told me this theory would never wash in the halls of academia."  Then he continues, "let us put forth, not as a fact but as a distinct possibility: Luke might have been a slave" (emphasis original).  And that's fine---I agree, it is a reasonable hypothesis.  But it just doesn't have any good evidence behind it, at present.
Let me also say something about Dick Harfield's answer.  He is correct that Luke-Acts is anonymous, and unlikely to have been written by Luke the companion of Paul---although I disagree that this is relevant to your question.  But he makes a good point that the tradition about Luke being a physician is not well-established, since it comes from an epistle (Colossians) which is likely to be pseudepigraphical.  On the other hand, whether Colossians was written by Paul or not, it is certainly very ancient, and so we have reason to trust it when it affirms Luke as a physician.  And I think Harfield has a decent point about Luke being referred to as among his "fellowlabourers."  It is, as DJClayworth has pointed out, quite plausible that a slave might be referred to as such.  But it seems more likely to me that Paul considered Luke to be closer to his own social standing.

