# Is there a word for this?



## cinderblock (Oct 13, 2015)

We have a word for shadow, but do we have a word for the "shadow" of a speed blur?

For example if you were traveling really fast, you might see replicas of yourself behind you.


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## Riptide (Oct 13, 2015)

Are you looking for afterimage?


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## LeeC (Oct 13, 2015)

To my understanding, there's no specific evocative word for speed blur (more commonly called motion blur). 

To allude to such in writing one might say "streaked by/along," "blinding speed," "he saw only the blurred afterimage" [with a nod to Riptide], "the rapid movement was indistinct," "faster than the eye could distinctly capture," or whatever is appropriate to the action depicted. 

A better way to approach your quandary would be to post an extract containing the action, to see if your trial wording is evocative to others, and if not what suggestions they might have.


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## Cran (Oct 13, 2015)

cinderblock said:


> We have a word for shadow, but do we have a word for the "shadow" of a speed blur?
> 
> For example if you were traveling really fast, you might see replicas of yourself behind you.


Well, no. It's a popular misconception, and you would see some really weird versions of things, but not your own time shadows because you have already distorted and destroyed those photons by your motion through spacetime. At relativistic speeds, the spacetime in your slipstream is devoid of photons until the photons that were behind you at your breach point (the point in spacetime when you reached or exceeded the speed of light) catch up with you. To look back, it's as though you were never there.

OK. So, using your hyperlight speed, you dash from point A to point B. Then, before the residual photons have time to catch you at point B, you teleport instantly to point C, which as far from points A and B as they are from each other (ie, you are at the apex of an equilateral triangle), and you look. 

Comic books, movies, and similar imaginations tell us that you see yourself moving across your line of sight, perhaps stretched and blurred as the photons which bounced off the dashing you reach the observing you almost all at once. Relativity tells us that, at best, you will see a tiny burst of light and the afterimage will be a line, because from the observer's point of view, the dashing you will have collapsed to a pinpoint. As you approach the speed of light, an observer will see that the dimension along the line of motion gets smaller and smaller. This effect is independent of the Lorentz-Fitzgerald Contraction, which is an optical effect in which an observer will see both the side and the back of the object in motion.

For the dashing you, moving from A to B, you will see the spacetime ahead of you begin to twist - this is called the Penrose-Terrell rotation, which is like the L-F contraction but for the moving observer. The result is often likened to scenes from Escher.

But, that was not your question. The terminology of imagined light effects or optical illusions is not really established. Those already suggested - speed or motion blur, afterimage (although that also relates to retinal effects), time shadows - are as good as any that might be applied.


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## ppsage (Oct 13, 2015)

Back when I used to see stuff like that, we called it strobing. "I'm really strobing, man. I can still see that chick on the bike."


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## cinderblock (Oct 14, 2015)

ppsage said:


> Back when I used to see stuff like that, we called it strobing. "I'm really strobing, man. I can still see that chick on the bike."



Do you mind giving me an example of when you used this? Sounds really poetic. Like, do you use this when you're reminiscing something? 



Cran said:


> Well, no. It's a popular misconception, and you would see some really weird versions of things, but not your own time shadows because you have already distorted and destroyed those photons by your motion through spacetime. At relativistic speeds, the spacetime in your slipstream is devoid of photons until the photons that were behind you at your breach point (the point in spacetime when you reached or exceeded the speed of light) catch up with you. To look back, it's as though you were never there.
> 
> OK. So, using your hyperlight speed, you dash from point A to point B. Then, before the residual photons have time to catch you at point B, you teleport instantly to point C, which as far from points A and B as they are from each other (ie, you are at the apex of an equilateral triangle), and you look.
> 
> ...



Wow, I'm not sure I understood everything you said, but I really appreciate that breakdown. 

Fortunately, the mention of the "time shadow" or whatever I end up using, is more of a figure of speech, independent of scientific accuracy. 

But I just learned something new. So you're saying no matter how fast you travel in a circle, you'll never catch up to yourself, or see your back? 

Is this set in stone? Or is it theory? 

'Cause last I heard, there's been some kind of shakeup that may require rewriting law of physics. I think I heard about it on Radio Lab, where they came up with this new technology that could move an object without pushing it, or something like that. It was called N motion or something. 

By the time they figure out time traveling and teleportation, the whole book on physics will have been rewritten multiple times over. And I believe time traveling/teleportation is an inevitability. It's just a matter of when. There isn't anything that's impossible. Technology never plateaus. 



LeeC said:


> To my understanding, there's no specific evocative word for speed blur (more commonly called motion blur).
> 
> To allude to such in writing one might say "streaked by/along," "blinding speed," "he saw only the blurred afterimage" [with a nod to Riptide], "the rapid movement was indistinct," "faster than the eye could distinctly capture," or whatever is appropriate to the action depicted.
> 
> A better way to approach your quandary would be to post an extract containing the action, to see if your trial wording is evocative to others, and if not what suggestions they might have.



Thanks, I would've certainly posted the line, but it's used in the middle of a long, dramatic scene in the story. Without context, it would be hard to understand, and from my experience posting here, one-liners have gotten bashed because people read it without context and say they don't understand. And yet if I post the whole scene, it'll be too long. Hmm. I'll try writing the whole thing out and testing it to some people later.


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## Cran (Oct 14, 2015)

cinderblock said:


> Wow, I'm not sure I understood everything you said, but I really appreciate that breakdown.
> 
> Fortunately, the mention of the "time shadow" or whatever I end up using, is more of a figure of speech, independent of scientific accuracy.


Fortunately, fiction and popular concepts don't have to conform to the science of the day. We are used to motion blur and time shadows and leaps into hyperspace.




> But I just learned something new. So you're saying no matter how fast you travel in a circle, you'll never catch up to yourself, or see your back?


No, only if you look back along the path you've traveled. If you take a circular track, then you can encounter the photons you haven't absorbed or destroyed, so that, yes, you can see your back up to the point when you become a point (ie, when you breach the light barrier). After that, you would see the photonic boom (the flash of light; it's like a sonic boom but in light instead of sound).

From here, any theory or test we can do now ends, what you as a C+ observer would see of the C+ object in a generally twisted environment is pure speculation.



> Is this set in stone? Or is it theory?


Nothing is set in stone (other than fossils), but the theory (and don't underestimate what scientific theory means) is supported by particle physics experiments (because particles are the only things we can accelerate to anywhere near C). 




> 'Cause last I heard, there's been some kind of shakeup that may require rewriting law of physics. I think I heard about it on Radio Lab, where they came up with this new technology that could move an object without pushing it, or something like that. It was called N motion or something.


Not rewriting laws, but challenging and perhaps rewriting theories; yes, these things happen. Sometimes, it turns out to be observer error; sometimes, it adds a new wrinkle to quantum physics as it is known on the day. 

The latest I am aware of is the estimate of quantum entanglement speeds (which is a Schrodinger-type experiment with photons instead of cats); recently determined at ten thousand times the speed of light. 

N motion? That's usually applied to classical physics - N is the symbol for newtons (the energy or force needed to accelerate one kilogram by one metre per second per second). N motion is usually described as a vector (ie, a force which has magnitude and direction). Mathematically, n is a simple variable, usually a number. If there is a new definition for N, I am not aware of it. 




> By the time they figure out time traveling and teleportation, the whole book on physics will have been rewritten multiple times over.


Why? Both are already allowed in current physics theory. Time travel does not overturn Einstein's theories of relativity - it's a consequence that's been discussed for nearly a century. Teleportation is a theoretical consequence of quantum entanglement; that's why they are doing the experiments and measurements now.


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## JustRob (Oct 14, 2015)

Blinkin' 'eck Cran! 

There's a line in my novel (Strangely there often is, as you may have noticed, but that's beyond the comprehension of current scientific thinking about quantum entanglement.) which reads "if you suggested searching for a solution in string theory I’d start wondering why you’re a policeman." Given the authority with which you write I'm starting to wonder what the people in Goomalling get up to there. Is there something we should know?

I seem to recollect that one of my cameras, which often have features that I don't fully comprehend, had a reverse blur function. The problem was apparently that when used in its normal mode the camera would produce a picture of a speeding car with the speed blur in _front_ of it, something that is depicted as representing FTL travel in sci-fi programmes. The reverse blur function corrected this so that the blur appeared _behind_ the car as one might normally expect. I think it was to do with how the exposure varied during the shot. Tricky stuff anyway, cars apparently going FTL round Brands Hatch race track.


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## Cran (Oct 14, 2015)

JustRob said:


> Blinkin' 'eck Cran!
> 
> There's a line in my novel (Strangely there often is, as you may have noticed, but that's beyond the comprehension of current scientific thinking about quantum entangelement.) which reads "if you suggested searching for a solution in string theory I’d start wondering why you’re a policeman." Given the authority with which you write I'm starting to wonder what the people in Goomalling get up to there. Is there something we should know?


Not so much. Goomalling is a world away from science other than how it applies to farming. My university studies were aimed at planetary geology and geomorphology, although some of my professors were pushing for me to go into science journalism (because my work background was in general journalism).

Real life has put a brake on my studies, but not my interest.



> I seem to recollect that one of my cameras, which often have features that I don't fully comprehend, had a reverse blur function. The problem was apparently that when used in its normal mode the camera would produce a picture of a speeding car with the speed blur in _front_ of it, something that is depicted as representing FTL travel in sci-fi programmes. The reverse blur function corrected this so that the blur appeared _behind_ the car as one might normally expect. I think it was to do with how the exposure varied during the shot. Tricky stuff anyway, cars apparently going FTL round Brands Hatch race track.


The normal blur (the blur in front of the vehicle) also shows up in time exposures of the sky as streaks starting from a point. The point, or relative clarity of the moving object in its initial position represents the beginning of the exposure time (when most of the photonic information is captured). The reverse blur function is an excellent bit of technology that fades in the exposure instead - it effectively alters the relative opening and closing shutter speeds by slowing the shutter opening so that the majority of photonic information is captured towards the end of the exposure.


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## Bloggsworth (Oct 14, 2015)

JustRob said:


> Blinkin' 'eck Cran!
> 
> I seem to recollect that one of my cameras, which often have features that I don't fully comprehend, had a reverse blur function. The problem was apparently that when used in its normal mode the camera would produce a picture of a speeding car with the speed blur in _front_ of it, something that is depicted as representing FTL travel in sci-fi programmes. The reverse blur function corrected this so that the blur appeared _behind_ the car as one might normally expect. I think it was to do with how the exposure varied during the shot. Tricky stuff anyway, cars apparently going FTL round Brands Hatch race track.



This can happen if the camera is panned contrary to the movement of a planar shutter curtain, for which reason, vertical shutters are better for recording motion.

Were one to travel faster than the speed of light, one would be seeing into the past as one would overtake the light which left your point of origin before you departed but, of course, they would only be photons so would be incapable of reorganisation as they would always be receding relative to the viewer. We may be able to view the past, but we could not interfere with it, so no chance of preventing the _Massacre of the Innocents_, or the colonisation of Australasia...


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## JustRob (Oct 15, 2015)

Another mechanism for collecting the majority of the photons at the end of the exposure is the option to fire an electronic flash just before the shutter closes. Normally the flash occurs as soon as the shutter opens and this can cause the forward blur with a long exposure time. In cameras with focal plane shutters this option was known as second blind synchronisation, which did explain what it was but not why one would ever need it. Nowadays cameras are so intelligent that they often only need to know what you want to do and don't need to be told how to do it. I still like to have a camera which allows full manual control for unusual situations though.

I agree about the panning problem. I have spent the odd day trackside trying to get the motion blur on racing cars right. Any decent shots that I got were more by luck than skill. If you track the car's motion too well it appears that it is stationary and the background is moving, which looks particularly weird. I don't suppose that there's a word for that phenomenon either, unless it's "relativity".


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