is it true?

How fast does a shadow move?

There is shape, height and width information for a start

furious said:

How fast does a shadow move?

and information over space and time

>How fast does a shadow move?

Yeah was thinking more for starters say observing shadows, their correspondence with movement of the body, for example. Now I know this is deriving information from what is around the shadow, and these tend to be not perfect shadows/darkness, but indulge me for a moment.

Wasn’t thinking so much the usual things that come up with this subject.

To kick the subject off, can you exist without the possibility that your body, for example, will cast a shadow given a point source of light some distance away will enable this.

Like, if it is a sunny day late afternoon, and your body courtesy the sun are making a shadow, is it the case that you wouldn’t exist without that shadow?

A crazy indulgence, but maybe fun.

CrazyNeutrino said:

furious said:

How fast does a shadow move?

and information over space and time

if the shadow is moving there will be directional information as well

CrazyNeutrino said:

CrazyNeutrino said:

furious said:

How fast does a shadow move?

and information over space and time

if the shadow is moving there will be directional information as well

the sunlight will also give clues to time and day

there could be reflected information as well

some information regarding a lack of holes might be wrought from its depths

Like, humans and other animals have evolved with the physics of the world casting shadows, I can take my dog and sheep out for the regular evening walks to urinate etc, torch being the only light, and can change the elevation of the torch to make larger(and longer shadows – distorting body shape shadow in fact), and the nimals are not bothered by this.

I am wondering of the physics lesson from this going back through biohistory – the extent it has influenced evolution.

• and can change the elevation of the torch to make larger(and longer shadows – distorting body shape shadow

Just like the elevation of the sun and moon can change and distort shadows as a result?

>Just like the elevation of the sun and moon can change and distort shadows as a result?

That’s the one.

Was also thinking perfect shadows are hardly found in nature, especially if you include IR range. You maybe get perfect shadows(excluding low IR) within hollow things.

Was wondering of the generalizing from the (abstract extreme) example of the ‘no information in a (perfect) shadow’, this doesn’t inform much of the reality of what may be gotten or happened upon from the more typical imperfect examples of shadows that inhabit reality.

define “perfect shadow”.

furious said:

How fast does a shadow move?

As fast as you like. The speed of the movement of a shadow isn’t limited to lightspeed. But that can’t be used to transmit actual information faster than c.

…

transition said:

To kick the subject off, can you exist without the possibility that your body, for example, will cast a shadow given a point source of light some distance away will enable this.

Like, if it is a sunny day late afternoon, and your body courtesy the sun are making a shadow, is it the case that you wouldn’t exist without that shadow?

A crazy indulgence, but maybe fun.

Huh? That sounds like you’re putting the cart before the horse.

Under those conditions, any opaque body will cast a shadow (assuming there’s a suitable surface for the shadow to fall on). So it makes sense to say that your shadow can’t exist without you, but saying that you can’t exist without your shadow seems like a blatant reversal of causality.

>Huh? That sounds like you’re putting the cart before the horse.

yes I am, but consider I mentioned “the possibility”, and what is possible exists before, then after something happens the reality displaces other possibilities or the same thing happening again in the same space(at the same time).

It’s silly on the face of it I know, but just indulge me for a while.

seeing as we’re making shit up that has no basis in physics then i guess anything can happen.

you still haven’t define a perfect shadow.

ChrispenEvan said:

seeing as we’re making shit up that has no basis in physics then i guess anything can happen.

you still haven’t define a perfect shadow.

Who knows what evil lurks in the hearts of men?

The Shadow knows.

>seeing as we’re making shit up that has no basis in physics then i guess anything can happen.

the thoughts and word formulation you strung together and projected above existed as a possibility, in ‘possibility space’ previous to you typing it in the box and posting.

did they?

everything exists in this make believe space but that doesn’t mean it will eventuate or is physically possible. it is lazy thinking.

>did they?

How does anything happen if there isn’t something providing for some chance of it happening.

How does anything happen if there isn’t something providing for some chance of it happening.

plus we’re talking physics not ideas and words.

Will get to the proposition of the perfect shadow later, I’m thinking it would only exist at 0deg Kelvin.

>plus we’re talking physics not ideas and words.

Just indulge things a bit. Be a little less dry, hard-nosed materialist for a moment.

i don’t work that way. i could say to you to not be so wishy washy when trying to talk science. as i said before if we don’t “stick to the rules” we wont get anywhere. even gerdanken experiments obey rules.

Until you tell us what you mean by the term “perfect shadow”, it’s a bit hard for us to proceed.

In one sense, all real shadows are perfect, compared to shadows that 3D rendering software generates. But I suspect that’s not what you’re getting at.

I suppose you could define a perfect shadow as one created by a totally opaque object illuminated by a single distant point-like light source in a vacuum. But even then, the edges of the shadow will be slightly blurry, due to diffraction effects. And somewhat surprisingly, there can be light in the middle of the region that you’d expect to be totally shadowed.

From Arago spot

In optics, an Arago spot, Fresnel bright spot, or Poisson spot is a bright point that appears at the center of a circular object’s shadow due to Fresnel diffraction. This spot played an important role in the discovery of the wave nature of light (see history section below) and is a common way to demonstrate that light behaves as a wave for example in undergraduate physics laboratory exercises. The basic experimental setup is shown in the figure on the right below.

Arago spot experiment. A point source illuminates a circular object, casting a shadow on a screen. At the shadow’s center a bright spot appears due to diffraction, contradicting the prediction of geometric optics

[…]

The images show simulated Arago spots in the shadow of a disc of varying diameter (4 mm, 2 mm, 1 mm – left to right) at a distance of 1 m from the disc. The point source has a wavelength of 633 nm (e.g. He-Ne Laser) and is located 1 m from the disc. The image width corresponds to 16 mm.

i was just reading about diffraction at the edges.

is there any connection between the above, without the arago spot, and an airy disk?

ChrispenEvan said:

is there any connection between the above, without the arago spot, and an airy disk?

Sure, since the rings in both cases are due to diffraction.

>i don’t work that way. i could say to you to not be so wishy washy when trying to talk science. as i said before if we don’t “stick to the rules” we wont get anywhere.

In that case give us a couple of paragraphs regards the physics lesson gotten from shadows, like what you’ve learned from your own since born (and those of other things in your external environment), and what of that were made possible courtesy what your ancestors passed on to you, I mean fairly clearly that’s the sort of territory I was considering.

The proposition regards something not being able to exist without a shadow (in the context given), though silly is true, it’s not entirely silly though as a shadow is a real thing, a feature of the physical world. Partly rhetorical for sure, but more thought experiment. It’s to do with the significance or importance that might be attributed a shadow, or more to the point the significance that might be attributed the reality of ‘shadowing’ potential.

Perhaps a question that gets to the heart of the matter would be – do shadows form faster than you move? Or at the same rate that you move?

How does a real shadow compare with the perception of a shadow, or the concept of a shadow?

a shadow would form with a lag governed by the speed of light and the distance from object to shadow location.

>a shadow would form with a lag governed by the speed of light and the distance from object to shadow location.

+ time back to receiver (eyes)+ processing (regards perception). In the case of a shadow it might be the absence of input within a given area contrasted with that illuminated around it. But add an array of ‘templates’ for processing/rendering that exist before processing for whatever example start.

So i’m in the territory of ‘anticipating a shadow’, and generally when walking around looking ahead with the sun anything other than directly above when the sun is behind you you see your shadow not yourself. When someone walks up behind you and the sun is behind you you see their shadow before you see them. They are preceded (into view) by their shadow.

Of the details that we might attribute an entity/object status to shadows, what’s a good starting point do you think?

A perhaps funny question – can you own your own shadow? Or, to unbias the language, can you own the shadow cast by your body.

that shadow
not and real
is to know
nothing appeal
no woes
none deals
is as goes
as looks’ feel
unsuppose
no speel
things arose
water like keel
darkness most
shadows’ real