system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do we know nothing can go faster than light?

If something were to go ftl wouldn't it be it be invisible? If so, how can we be sure nothing goes ftl?
gpt
No, something being FTL would not be invisible. However, it would only be seen at a location when it arrived, or by a nearby observer after it had passed. At that point, the observer would see two images of the object, the arriving image playing out backwards, and the passing image playing out normally. It would appear quite unusual.

Similarly, something being faster than sound doesn't mean it can't be heard, although you wouldn't hear it till it arrived. You'd then hear the preceding sound 'backwards' as it caught up, and overlapping any following sound if it continued on.