# I Capturing an instant of time

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1. May 26, 2017

### Physics is awesome

just wondering why no one has made a camera that can truly capture an instant of time. I'm talking about an instant which is defined as an instantaneous moment that has 0 duration. Why do all cameras have shutters that open for a specified amount of time instead of just capturing a true instant of time which has a 0 for actual time that is past. Basically what I'm asking is if an instant of time exists as part of the physical world which has a duration of 0 time why can't we capture this instant on a camera instead of a camera being exposed for a specified amount of milli seconds it should just be an instant which would then never produce a blurry image since it wouldn't matter how fast matter is moving.

2. May 26, 2017

### Staff: Mentor

You won't like this. A silly answer for a silly question. In zero time, zero light will enter the camera, so a picture of an instant is by definition just black. Therefore, all black pictures show zero time.

I suspect that you may have a better question than that, so think about it, rephrase it and try again.

3. May 26, 2017

### DennisN

A trick question for you:
If we had a clock that ticked not each second (nor millisecond, nor microsecond, nor nanosecond etc) but each what you call "instantaneous moment that has 0 duration", then how fast would that clock tick? How many ticks would it do, let's say, each minute?

4. May 26, 2017

### Drakkith

Staff Emeritus
Let's assume we have a brightly lit scene and my camera sensor is taking in, on average, 1,000,000 photons per pixel per second (this is close to a realistic number). So I go ahead and take a picture. Oh no! This is far too many photons for my camera sensor to handle! The entire sensor array is saturated and my image is pure white! What can I do about it?

The easiest thing to do is to simply reduce the exposure time. So I change my camera settings and set my exposure time to 1/10th of a second. Now my camera sensor is picking up 100,000 photons/pixel. Unfortunately, this is still too high and I need to reduce my exposure time again.

Okay, now my exposure time is 1/50th of a second and my camera sensor is detecting on average of 20,000 photons/pixel. Much better! Now I have a good looking image!

Notice that all of my exposures have been of non-zero duration. This is because over a timeframe of zero, my camera's sensor detects zero photons! I actually can't even make my camera record a duration of zero! Even the physical processes that have to happen in order for the camera to start and end its exposure require non-zero duration. It's simply not possible, and even if it were, I would detect zero photons anyways.

5. May 26, 2017

### scottdave

Ha! Just don't open the shutter at all, and as far as you know, it did open for zero time.