Comment by asimpletune | Hacker News Reader

Comment by asimpletune | Hacker News Reader

This might be a strange thought, but the idea of the global shutter got me thinking about the promise of a global shutter and the strange implications it could lead to regarding special relativity. I'm not an expert but, as I understand, one aspect of special relativity is that there is no shared now. Like, the idea of simultaneity is different than how we experience it, because two observers can literally witness a different sequence of events and there are no contradictions. (I hope I got that right)

In a traditional shutter, each row of pixels are read one at a time, so there is an inherit arrow of time. However, with a global shutter, each row of pixels is "exposed" simultaneously, theoretically. So what I wonder is what would be the implications of this with respect to special relativity.

For example, if a global shutter camera were used to adjudicate a close race, would it be possible for one row of sensors to witness a contradictory result with another row? Sorry if I'm not explaining this right but I'd be curious to hear what a more knowledgable person's thoughts on the matter are.

There are no implications regarding special relativity. The propagation speeds of the triggering signal are well understood. If for some insane reason it's not considered fast enough to simply ignore delays from one side of the chip to the other (wherever the sync signal comes in), it's straightforward to put in delay lines to ensure everything triggers at the same time to an accuracy that depends on the amount of silicon you want to lay down for those delay lines relative to the capacitors.

Most likely a couple nanoseconds one way or another don't matter (even at timescales of 1/80,000 s) and those ever-so-slight differences are ignored.

I meant in a theoretical sense, like as a thought experiment. If the shutter were an idealized, global shutter, where each row of pixels are exposed instantaneously, what would be the special relativity implications, if any?

Unless the sensor is half over the event horizon of a black hole I'm failing to understand how my answer doesn't short-circuit the thought experiment to ground.

If two global shutter cameras take a scene at the same time, they would have the same image. If they don't, then they wouldn't.

Global shutter cameras are also not new. CCD sensors are global shutter and we used to use CCD sensors for cameras decades ago until we switched over to CMOS for most applications due to their larger size and better dynamic range. I have a global shutter HVX200 from 2005 in my closet.

So the whole point of what I was saying is that special relativity proves that whether two spatially separated events occur at the same time is not absolute and it depends on the observer’s reference frame. My question has nothing to do with engineering and wasn’t intended practically.

The point was to imagine light from some event, reaching two parts of the sensor at the same time, being exposed at the same time (ie the global shutter), and yet asking if those two parts of the sensor could show conflicting versions of that same event, since they are nonetheless separated by space.

There is no problem. The sensor is a rigid assembly where all parts are motionless with respect to each other. Simultaneity is a well-defined concept for the sensor.

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