Good point. It makes me wonder if carbon dating anomalies have ever been found in the technology's history.I wonder what carbon dating would do with a "future" coin? Perhaps it could be done to find out how old the coin really is. Has anyone actually studied it?
What carbon dating essentially tells you is “how long has passed since the organic material in this object died, in its own frame of reference?”.
Of the Carbon that exists on Earth, approximately 1 in a trillion nuclei are an isotope called “Carbon-14”. C14 is radioactive - with a halflife of about 6000 years.
Whilst living things are alive, they constantly refresh the materials in their cells - so the C14 content inside is the same as the levels outside.
However - when the organism dies, this uptake stops - and the amount of Carbon-14 begins to decrease.
By comparing the measured levels of C-14 in an object, and extrapolating backwards using the halflife, you can then get a good estimate of how long has passed since the object stopped refreshing its carbon content.
We also couple this with historic data about the levels of C14, which makes it more accurate etc.
Obviously, nothing in this process allows us to tell if an object came back from the future.
Assuming C14 levels stay relatively constant, how could this method be used to tell the difference between a lump of wood which died in 1500, and a lump of wood which died in 2500, and was sent back to 2016 in the year 3000?
Both lumps have not been updating their carbon content for 500 years - so radioisotope dating wouldn't be able to tell the difference.
We might be able to tell if something funky was going on - if we do something to really screw up the C14 content of the planet, and we found organic material with 4000% of the natural levels of C14, then something weird will be noticed - but I doubt “time travel” will be everyone's first guess.
So: no. You cannot use radioisotope dating to determine if something is from the future. You can only use it to determine the length of time since something died - as measured by a local observer.