I'd like to know what you think. You said it's real, but not measurable. To me, that seems inconsistent, so I'm trying to understand what you're thinking. Measuring it is fairly trivial in principle, but the practicalities are something else. If we could have a timer precise to the millisecond moving on a rail at 100km/s, synchronized (by einstein synchronization) with a similar timer on a similar track 1000km away, then it could be done. Not Nobel prize worthy, I'm afraid.