# What do ants see?

After watching some ants in my garden today, and then looking at this very illuminating demonstration, I got to wondering, about what they would see. Not specifically ants (I understand their eyesight is quite poor), but similarly small, or even smaller creatures.

I guess I'm asking more about the nature of light and how photons are reflected off very small surfaces. Would a very small creature, like say, an ant, with vision, be able to see something as small as a single e. coli bacterium? or a virus? Would their world 'look' the same as ours or does the viewers relative size have a bearing on the quality of their perception?

And additionally beyond the realm of reality, if I could shrink myself down to the size of a bacterium, could I see atoms?

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 One of the unfortunate laws of nature is that to see more detail you inevitably need bigger and more complex optics. – Martin Beckett Jul 23 '12 at 20:28

Ants only have low-resolution eyes, aside from three ocelli - simple eyes - that only detect an overall light level and polarization, see

http://en.wikipedia.org/wiki/Ant#Morphology

Their ability to see details - small objects and their features - is much worse than for vertebrates like us. To suggest that animals - especially as primitive animals as ants - could see bacteria is preposterous.

The wavelength of visible light is about half a micron - which is also the size of many bacteria. So you can't see anything inside bacteria with the visible light, not even with cutting-edge technology. To see more detailed objects, you have to switch to X-rays or electrons and create better microscopes.

It's even more unrealistic to propose that one - or even an ant - could see an atom (which is 10,000 times smaller than a bacterium) through visible light.

You can't just scale things up and down. The world is not invariant under scale transformations, we say. Different length scales see different kinds of physical phenomena and different physical objects. The atom of a given kind has always the same size and you can't scale it up. Moreover, you didn't even do the scaling properly because you didn't scale the wavelength of the light. Also, vision with detailed resolution requires some "large enough circuits" to deal with the information etc.

By the way, this holds even for accelerators. The LHC is our best "microscope" that can see distances shorter than $10^{-19}$ meters - but to do so, it requires tunnels with the best magnets that are 27 kilometers long. Objects as small as ants can't see with this good resolution, and even if they could, they couldn't deal with the huge amount of information that their eyes would be giving to them.

Large enough animals - e.g. mammals - see the world much like we do. There are well-known differences between the colors that different mammals are sensitive to. Dogs are, for instance, partly color-blind, relatively to what we can do.

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The asker specifically stated in the question that the vision of ants was just a metaphor, and his question was about the nature of light. It is not "ludicrous" to propose the question, as you felt the need to state more than once. It is ludicrous to berate newcomers to this forum for asking questions, as you did to me just a moment ago (link follows), and to this asker just now. – Olhovsky May 9 '11 at 7:16
Dear Olhovsky, you're not right - or what's the right way of saying that you're wrong without berating you. ;-) The idea that one can see bacteria or atoms is ludicrous mainly and exactly because it contradicts the basic nature of light, namely that it is made of waves. One may use any metaphors but at the very end, physics has a content that is not a metaphor. In my country which is not at the cutting edge, the fact that the light is made of waves is being taught at basic schools so I reserve the right to say that people unfamiliar with this very point lack some basic education. – Luboš Motl May 9 '11 at 9:35
And if the issue is about newcomers, let me say that I find the recent flood of low-quality questions frustrating, indeed. The purpose of this server is not to attract a maximum number of random "newcomers" who write arbitrary sequences of words with at least one question mark. Just a few months ago, this was supposed - and nearly was in practice - a genuine server to ask and answer questions about physics by people who actually know some physics. - And thanks, Robert, by the way. – Luboš Motl May 9 '11 at 9:36
@Luboš, I agree the quality of Questions has decreased, but I think people who actually know some Physics are not asking Questions, for whatever reasons. When newcomers arrive, they immediately find examples of Questions that seem to them more stupid than their Question, so why not ask it? The hard Questions are hard to find, and are quite likely not to be Answered. If there were a preponderance of hard Questions, the low-quality Questions might be put off. What newcomers don't see, so they're not put off by them, are the Answers that tell the low-quality Questions that they're stupid. – Peter Morgan May 9 '11 at 12:10
@Sam I am sorry you had to go through this, which could have been avoided if you had read the link you provided more carefully, because it has all the numbers. Do not be discouraged, many of us have been through this with Lubos, if not here, on his blog, when we manage to blow his short fuse. He is a great teacher though. – anna v May 10 '11 at 4:30

The ant world is ordered far more by chemical reception and pheromones than by vision. Ants produce an array of such chemicals which act as signals. They also sense other chemicals in their environment, and as what might be called a “super organism” they have some collective map, a chemical map, of the terrain they inhabit.

Ants have compound eyes, and they are pretty small. For the most part their purpose is to sense sudden changes in light levels. An ant which perceives such then gets a signal that some predator might be present and so getting out of there is in order.

Some species of baceteria have opsin molecules that are photoactive. So the reception of photons can result in changes in molecular pathway activity. The rhodopsin molecule in our eyes or retina has two conformal states for reception and nonreception of a photon. The energy of the photon changes the shape of the molecule and this then acts to initiate a GTP molecular pathway which is amplified ultimately into a neural action potential. Rhodopsin is one form of opsin molecules, which in their general classification overlap with photosynthetic molecules in some bacteria as well. However, the bacilli do not form any sort of image of anything.

In order for a bacillus to “see” an atom they would need to detect gamma rays. Gamma rays are largely outside the EM spectrum available to biological systems. In fact they are lethal.

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 I see you were demoted once again :) . – anna v May 10 '11 at 4:37 I've merged the two instances of your account(s). You can flag for moderator attention when that happens. – dmckee♦ May 10 '11 at 14:12

As far as the function of light goes: Yes you can scale down (to a point). I have worked on an ASIC (Application Specific Integrated Circuit) which used an 8 micron process (Cro-magnon by today's standards). I could not see the detail of these circuits in the finished product (far too small) BUT they were made basically (I am greatly simplifying) with itsy-bitsy photographic images produced by light (beyond the range of visible light). To say it another way: the resolvable detail available from light is far, FAR finer than the un-aided human eye can see.

Biologists claim that eagles can see about 10x sharper detail than a human (and an eagle's eye is noticably smaller than a human eye).

What I don't know, is where the physical size of the eye limits detail. I see no reason why it couldn't scale down... WAY down. But I am not a biologist and (thankfully) not an ant. It would be interesting to find out where the smallest eyeballs end and where other seeing apparati take over.

So, your example of getting down to where you could see bacteria presents an interesting break point: There is theoretically no problem seeing a bacterium (size about 1000 nm) at the lower end of UV (upper end of human-visible) light, wavelength about 400 nm. But detail would obviously be a bit hazy. The bacterium would appear as a blurry blob, and no glasses would help. The theoretical limit for modern optical microscopes to resolve detail is 200 nm (using 550 nm "green" light).

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