wolram said:
I guess every considered opinion about cosmology is right, as Marcus said, we could send robot probes into deep space but will we ever? we all know political opinion changes several times in our own life time, how could we hope for continued funding of an experiment that would take 10s of years.
My biggest concern is the rubber ruler, we can take thousands of measurements using light
as the ruler ,but will we ever know if light is playing tricks with us until after some deep space probe results?
Cosmology is not useless as many have said, even the spin offs in the science of building the equipment is valuable, how we value any results measurements from the cosmology of today is the question of futility.
One way to get a handle on what the universe looks like far away from us is to look at light that is deflected off of dust elsewhere in the universe. There have been, for instance, some measurements of supernovae from observing them lighting up dust far away from the explosion. There are also measurements of how galaxy clusters interact with the light from the cosmic microwave background (the Sunyaev-Zel'dovich Effect).
Another consideration is to look at the universe in things other than electromagnetic radiation. Observations of high-energy cosmic rays are beginning, with the Auger observatory reporting some interesting results that appear to show that a significant portion of the highest-energy cosmic rays may be coming from relatively nearby quasars. There are also gravitational wave experiments in the works. One day, we may even be able to measure the cosmic neutrino background (the idea here is basically the same as the cosmic microwave background, just with neutrinos, though neutrinos are vastly more difficult to measure, particularly at the low energies required to observe this background).
But even before we go to these other options, there are a multitude of ways to measure the properties of cosmology just with telescopes that observe radiation. We've got the anisotropies in the cosmic microwave background, we've got the polarization of the CMB, we've got supernova observations, we've got galaxy cluster counting experiments, we've got baryon acoustic oscillations, we've got cosmic shear observations, we've got weak and strong gravitational lensing of massive systems, we've got X-ray images of clusters, we've got infrared and sub-millimeter images of extremely distant galaxies, we've got 21cm experiments to detect the epoch of reionization, and I'm sure I'm missing a number of things. The point is, though, that by measuring the exact same theoretical parameters using all of these various analysis techniques, we get independent checks that we're not totally mistaken as to the nature of what's going on.
If there was a fundamental flaw in the big bang theory, for instance, then we wouldn't expect different experiments that measure entirely different observables would agree. And yet they do agree, again and again and again. So we can be pretty darned confident that the overall picture is at least approximately accurate.