# More Puzzling "Physics"



## Ursa major (Nov 7, 2008)

I've been reading some books recently (Ilium, Olypos, Hyperion) where some of the characters are able to move so fast that they seem to blink in and out of existence.

Put to one side whether this is feasible (even though this is SF, not Fantasy like, dare I say it, Heroes), and whether the characters would burn up, etc.

What bothers me is how these characters seem to operate in normal light, both in the sense of how bright things are and in the wavelengths that they can see. It strikes me that brightness is dependent on the number of photons in a given period of time. If your timeframes are reduced by a factor of thousands, why aren't you groping around in the dark? And if your physical processes are speeded up, wouldn't you perceive different wavelengths of light?


*Awaits the scorn of physicists*


----------



## chrispenycate (Nov 7, 2008)

Not scorn, no. If you were moving really fast, there would be colour shift. Mind you, atmospheric friction would be a killer by that sort of speed. But if you were merely existing very fast, there shouldn't be any real problem with luminance levels. The photons are still there, you're just getting them from slightly different directions.

After all, how fast would you have to move to seem to appear from nowhere? A kilometre per second? That's a three hundred thousanth of the speed of light.

By analogy with sound; your neighbour's offspring's moped doesn't make any less noise when it moves twice as fast, it just goes away faster.


----------



## Ursa major (Nov 7, 2008)

I was think more of the eye being like a camera, in this case with a very much faster shutter speed: wouldn't less "exposure" lead to less light captured?

(I'll stop that analogy there, because I'm not much of a camera person.)


----------



## skeptical (Nov 9, 2008)

The appearance of them not being there, and suddenly appearing would be more of a limit on human perception, rather than photon speed.   We simply cannot see anything so fast.

Imagine a bullet flying at more than the speed of sound.   We cannot see it go past, but the speed of light would make vision from that bullet fine.   In fact, high speed jets go just as fast, and the pilots have no problem seeing.


----------



## Ursa major (Nov 9, 2008)

Thank you for your patience, gentlepersons. (I feel I'm stumbling about in the dark, even if no one else is. )


Let me cut to the chase; in _Hyperion_, there is a more detailed description of the effect:



> Then it came to him: besides the thickness of the light and his enhanced perception of energy fields, nothing was moving.


 


> ...but Kassad noticed that now even their acquisition radars - visible to him as concentric purple arcs - were motionless.


 

First, I'm not sure what "thickness" means in this context, but that's a minor quibble. Then there is the fact that Kassad can see the arcs of radar (presumably microwave) at the same time as visible light - which is a clever trick if you can do it, but one might imagine - if one were being generous - that Kassad's perceptions are being mediated in some way.

Finally, the microwave emissions are not moving - which suggests that Kassad is operating at at least the speed of light. One is then left to wonder how Kassad could _see_ EM radiation that appears at rest. What mechanism is being used to transmit the image to the eye? (I feel I'm having a "you can't hear in a vacuum" moment; or, perhaps more to the point, see a laser in a complete vacuum that is not pointing at your eye.)


----------



## chrispenycate (Nov 10, 2008)

If the radar is stationary, then he's moved out of Einstinian physics into something else, probably magic.

The "thickness" of a beam of light would be the time it was emitted, times the speed of light in the particular medium. i.e. in air, a microsecond pulse would be about three hundred metres thick (engineer's approximation) 

To detect microwaves, you'd have to have very big eyes, as they are (relative to visible light) very long wavelength. Or you could use a different sensory organ – it seems likely that moths detect microwaves with their antennae – and translated into visual images as the best way of letting the brain understand it.


----------



## Nik (Nov 10, 2008)

Relativistic doppler shift ??

Um, scary heat-shield issues aside, if incoming radiation is dopplered into visible region, your ordinary eyes should suffice...

This effect is familiar to astronomers, when visible emissisions from scary-distant, rapidly receding ancient quasars etc are dopplered *down* towards --Or *beyond* red-- as (in)famous 'RedShift'...

( I'll carefully side-step protests from 'tired-light' and related factions pending presentation of appropriately extraordinary new evidence... ;- )

Um, the radar scan appears to have stopped ? 
That sounds like time-dilation, the effect, IIRC, that lets cosmic rays' muon cascades travel unexpected distances into atmosphere before decaying. In *their* rest-frame, their clock's ticking as usual. In ours' they're running verrrry slow...

Snag with invoking time-dilation as explanation is, of course, the relativistic speeds required, and the consequent lack of time for character to react before crashing into landscape as an 'Extinction Level Event'...

Note that even in near-planet 'vacuum', there's still enough gas and particle density to really sting a sizeable relativistic object. Hence ST's 'Deflector Array', and lesser crafts' deployment of layered impact-buffers, 'sweeper' dust-clouds etc etc. And, even at ~0.1c, well below real 'Einsteinian' country, the smallest dust grain will strike like a cannon shell, a pebble as a tac-nuke...


----------



## Ursa major (Nov 10, 2008)

chrispenycate said:


> If the radar is stationary, then he's moved out of Einstinian physics into something else, probably magic.


 
That was what I'd assumed, frankly, i.e. this part (at least) of the story was fantasy.


----------



## ManTimeForgot (Dec 23, 2008)

Ursa major said:


> That was what I'd assumed, frankly, i.e. this part (at least) of the story was fantasy.




Don't be too sure about that.  When talking about velocities of the speed of light + using the Lorentz factor for determining time dilation crumbles.  You can't very well take the square root of 0 or a negative number and expect a meaningful answer.  

But... If something were moving FTL (like a tachyon; which coincidentally has negative energy requirements: it moves faster the less energetic it gets) at a truly ludicrous velocity, light waves might appear functionally motionless, and you wouldn't need Time Dilation to explain the effect.

Of course, a _catastrophic_ problem with moving this fast is how to get information to you in time to prevent yourself from being rendered into energy scattered across the universe (much less than vapor since the material of your bodies would _presumably_ be mass-energy converted).

MTF


----------



## Ursa major (Dec 23, 2008)

I'm not going to worry about it: not one of the Dan Simmons books that I've read is worth the effort or the time.


----------

