h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

They can say, "So long and thanks for all the fish," though.

is not the surface of the water reflective from below as it is from above? if it is reflective it would make sense that any underwater creature liable to head for the surface would be aware the image is itself.

Then 3 seconds later go back to make sure. Then 3 seconds later go back to make sure. Then........

Actually, they probably just avoid the surface.

As no-one seems to have pointed this out so far...

Greenland cannot vomit underwater.

RF

I refer the honourable gentleman to post 2,311

I bet you just said that so we'd all go back and see what it said.

"is not the surface of the water reflective from below as it is from above? if it is reflective it would make sense that any underwater creature liable to head for the surface would be aware the image is itself."

Maybe, but the reflection in the surface from above, which would probably be rather like the image from below, isn't very good because the surface isn't very flat, so they'd be aware of a dolphin but I doubt that they'd know it was them.

the entry on reflection at wiki (yeah, i decided to check) has a very good pic of a surface reflection from below. i think any creature continually breaking the surface, as dolphins must in order to breathe, would fairly rapidly work out the image coming towards them is not 'real'. this must surely apply to fish in tanks as well.

it's a further step again for the creature to deduce that the image is 'itself', and i am not convinced we can actually know this for certain, even if the creature is exhibiting an awareness that movement is mirrored.

and we've all seen the old film gags where the guy removes the mirror and copies the guy looking into it.

either way, reflections are available to our cetacian overlords.

there is not a single entry for Xzateer in google

We'll see about that.

I've never seen that screen before. How interesting.

Incidentally, it's because "Xzateer" is not a word. What I think you mean to say is "Xyster", which is a tool for scraping bones. Also a really cool word to use in Scrabble.

very useless : there is site called xyster.com
Not too sure how many hits it had before half of the H2G2 population rushed to have a look...

there is an even less useful site called xyster.net (that is the one I originally meant to mention).

quote
Incidentally, it's because "Xzateer" is not a word. What I think you mean to say is "Xyster"
\quote

i actually just tried to make something that does not yet exist on h2g2 as name and that sounds nice to me... it came out Xzateer... never heard of Xyster though..

I feel the need to clarify some of this water reflection confusion.

You cannot see your self very well in a reflection at a medium boundary (such as water/air or even water/glass in an aquarium).

The reflection seen at the water surface from below is a case of total internal reflection (TIR). This is a phenomenon caused by the difference in the refractive indices of water and air. Light is partially reflected and partially refracted at the surface UNTIL the the angle of incidence reaches the angle that the light will be refracted along the surface. Any shallower angle of incidence will cause all of the light to be reflected. This is what it involved in fiber optics and reflecting prisms.

What you see when looking up while under water is a circle. Anything above the surface can be seen inside the circle but outside of the circle you see reflections of things under water around you. So, while there is some image reflected directly back at the viewer, it is usually obscured by the image of what's beyond the surface.

and assuming there is like... sky around... not much to obscure the reflection now is there?

Nothing but nice bright sky...

Try it.

what? the sky?

nay... i prefer solid ground...

i don't think there is any confusion.

reflections occur underwater.

assuming dolphins break the surface several millions of times in their lives, 'unusual' or not, it will still be a phenomenon they encounter regularly.

there are ample photographic and film depictions of underwater surface reflections. and even jack custard was never wet as often as a dolphin. *s*

To see your own reflection the angle of incidence is 90 degrees. NO TOTAL INTERNAL REFLECTION. You do NOT see your own reflection. I have personally observed this.