The latest, most accurate data is depicted here:
The older, less accurate data is shown in red. The more accurate data are shown in blue, plus the data point in black.
Note that the error bars of blue and black data points all straddle the line denoting the change in the Fine Structure Constant, alpha, being equal to zero.
The Fine Structure constant, alpha, includes terms representing the speed of light and the charge of an electron. Ergo, if the speed of light has changed during the history of the Universe, it should manifest itself as a change in alpha, as observed at various redshift distances corresponding to earlier eras in the history of the Universe.
This data, published in December 2005, is compatible with there having been no change at all in alpha, and hence the speed of light, over cosmological time scales.
This has been a great thread and I will hate to see it pass.
For us uninitiated buffs it has been challenging, informative, confusing and enlightening. It makes me wonder a bit what my life would have been like had I followed my EE degree with graduate studies in physics instead of business. I expect though with my limited insight I made the right financial decision after all. Having said that, and appropriately admitted my lack of insight (but amazement nevertheless) into the realm of quantum physics, I am puzzled by a constant that is expressed in space dimension and time but must have preceeded both (and both of which are variables?) since it seems here at least that space and time were both "created" (or determined) immediately post the BANG.
Anyway it seems that there is some debate on the "constancy" of the Fine Structure Constant so I'll reserve judgement I guess. Clearly I'm not equiped to debate only inquire and it will not change the taste of my chocolate pie. In that I take no small comfort. FSC is also an enigma to me since it must have emerged after "c" as it seems to depend on the electron which was unavailable at T-0... would seem to make is a questionable yardstick for "c"..oh well there is much I'm not equipped to understand..Thanks to all for an enlightening thread.
BTW, I asked the question about "c" in the first place because I wondered what rules would be turned on their heads if for example "c" was infinite at T-0 and 0 at T-max. (approached the asymtotes). It would have helped me rationalize how all matter could expand from a marble to fill the universe uniformly in 10^-35 secs..(and where "t=c" near the origin). I also understand it would help bridge the gap between Einstein and Bohr but I'm not sure why. My wife tells me I should worry about the gas bill. I will do that right after the chocolate pie. Thanks guys.
Oh. longshadow, can you give me a ref for the chart on FSC? I'd like to read that piece of work. (hoping its a web link since my scientific subscriptions are as sparse as the local library on these topics) Damn this is fun!