I lose track of how many times I've heard an argument against something in physics because "we can't see it". I've even heard an engineering professor once argued with a student about electrons by asking the student "Have you seen an electron?". This issue came out again in light of the recent news flurry about the apparent discovery of the Higgs, and some moron somewhere continues to belittle high energy physics, and physics in general, about imagining such particles that we "can't see".
Of course, there are several ways to attack such stupid (yes, STUPID) arguments. The first is the question on what we mean by "seeing". Often, most people simply meant seeing something with the human eyes. But what exactly does that mean? If these people were to think carefully, it means a series of events that must occur: (i) visible light from some source hits an object; (ii) light from that object travels to our eyes (iii) our eyes then transmit electrical impulses to our brain (iv) we detect that object visually. That, my friends, is what is meant by seeing with our own eyes.
Next, by the above description, it is clear that our eyes can only see electromagnetic radiation, and not only that, it can only see it within the visible spectrum, which isn't very much. Thus, if something either does not emit EM radiation, or if the radiation is outside of the visible spectrum, we can't see it! Let's go back to our friend the electron. It is a charge particle. Our eye cannot "see" it even if it hits our eyeball! But can we still see it? Sure we can! Enter a cloud chamber! When an electron, especially high energy ones, moves through a cloud chamber, it ionizes some of the air/gas/water vapor molecules. This creates a nucleation site for water vapor condensation, leaving a cloud trail in the chamber. There, you have seen an electron. One could also argue that our eyes are not the only "detector" around. We can also use our other senses. We can't see wind, but we can hear and feel the moving air. We can't see heat/IR, but we can certainly feel it on our skin. Our eyes is only ONE of the "detector" that came with our bodies.
And speaking of the human eyes as detectors, anyone who has done anything with detection instruments can tell you that the eyes is a very bad detector in many cases. Sure, it has a very high spatial resolution, but man, it sucks everywhere else. For example, look at this figure that shows the sensitivity of the human eye over a range of frequency and also its response sensitivity.
Compare to other devices, the human eye has 2 very clear shortcomings: (i) the range of wavelength it is responsive to is extremely small; and (ii) its sensitivity (i.e. quantum efficiency, or QE) is quite low. It has a peak QE of ~1% at around 550 nm. What this means is that out of 100 photons that come in, it can detect, on average, only 1. Compare the range and QE of Vidicon and CCD and our eye is a very poor light detector! And this is what some people are using as the sole criteria of what's real and what isn't? Is this rational?
As with many things that a lot of people spew without thinking, the debunking of such things often are quite simple IF one has a little bit of knowledge, and the the ability to analyze the situation. Analyze what it means by "seeing", and then analyze the "detector" that is being use as the criteria. And apply such techniques to the pile of manure that one often hears in the media from politicians, etc., assuming you have such patience.