First of all, science doesn't 'prove' anything. Those who like to use this term try to use it in a 'absolutist' way, such as with mathematical proofs, when their actual model is the much weaker standard of 'proof' used in the legal system. The weakness of legal 'proof' is demonstrated by the fact that the legal system usually has a system of appeals, except perhaps in totalitarian states. Those who distort the definition of 'proof' often like to mangle the definitions of scientific 'theory' in much the same way. To avoid diverging too much on this side issue, those interested should read:
- The Scientific Method, part of Jose Wudka's class notes for his Relativity, Space-Time & Cosmology class;
- Truth and Proof in Science @ Relativity Online;
- The Problem of Induction @ Astronomy Notes;
- Hypothesis and Proof in Science @ Argonne National Laboratories.
We learn about the distant cosmos by two primary methods:
1) photons which arrive from distant objects.
2) high-energy particles (cosmic rays) which arrive from distant objects
For both of these methods, the information we measure includes their flux (number of particles per second per unit area), their energy (wavelength or frequency), direction and sometimes polarization.
Our ability to interpret what is going on 'out there' depends on one basic assumption: that it is physically consistent.
One characteristic of this physical consistency is our ability to predict some characteristic(s) of the system's behavior based on physical principles that can be expressed in mathematical form. That this mathematical process works as well as it does has been the subject of ongoing philosophical debates, such as described in “The Unreasonable Effectiveness of Mathematics in the Natural Sciences”.
How do we test this physical consistency? The primary method is that the objects we observe behave the way we predict. For example, we can predict the locations of planets in the solar system with excellent precision, decades in advance. This capability is used in everything from eclipse prediction to interplanetary probes.
Occasionally, we encounter situations where our predictions appear to break down. To maintain physical consistency, there are three possibilities scientists generally consider:
a) some approximation(s) used in the mathematical calculation are outside their range of validity and introducing larger errors in the calculation. Solutions to these problems may require increased computational resources which may or may not be available;
b) there is some additional known physics, not included in the original calculations, that should be included;
c) the most exciting possibility of all - new physics is being detected.
The history of science is loaded with examples of 'great problems' where the solutions were found through this method. Sometimes, finding these solutions takes a few years, but the process has been known to take decades. Notice that 'supernatural intervention' is not on the list. To illustrate this process, I will focus on two historical examples:
Initial measurements of solar neutrinos were one-third the expected fluxes based on nuclear reactions required to produce the observed luminosity of the Sun. Some creationists tried to claim that this was evidence that the Sun was not powered by fusion and could therefore not be billions of years old (see Evidence for a Young Sun, by Keith Davies). It would take over three decades, but real scientists would continue perusing the 'naturalistic' solutions, examining possibilities (a), (b), and (c). A number of refinements were made pursuing possiblities (a) and (b) but they did not improve the agreement in a significant way. Eventually, theories and experiments began to favor option (c), culminating in some experiments to actually test the hypothesis of neutrino oscillations, where the neutrinos oscillate between different 'flavors' when traveling through matter. Eventually experiments detected the mu- and tau- neutrinos from the Sun, which were created by oscillations of the electron-neutrinos created in solar fusion reactions. This was achieved by the Sudbury Neutrino Observatory. An Earth-based experiment measured neutrino oscillations more directly by passing neutrinos through the Earth to a detector (K2K Long-baseline Neutrino Oscillation Experiment Official Homepage). Also check out the Ultimate Neutrino Page.
The Theory of Gravity
Newtonian gravity was a great success in predicting orbits of solar system objects and even discovering the planet Neptune based on deviations from the predicted orbits. However, the orbital deviations of the planet Mercury proved harder to explain as many searches for a perturbing planet met with failure. The solution would eventually be found by Albert Einstein in 1915, during the development of his General Theory of Relativity. General Relativity was tested through a number of astronomical observations before it was possible to test in Earth-based laboratories. Today, general relativistic effects must be included when computing the signal propagation times in the Global Positioning System. Also check out Relativity in the Global Positioning System by Neil Ashby which illustrates the details of how this is done.
I have described a number of similar astronomical discoveries in my paper, “The Cosmos in Your Pocket. How Cosmological Science Became Earth Technology. I”, available at the Cornell Preprint server.
Also important in scientific testing is the question of reproducibility, . We cannot 'reproduce' astronomical observations in the laboratory sense. However, there are other ways to solve the reproducibility question, such as:
- We test by observing other similar objects, as in the case of supernovae and gamma-ray bursts;
- We can make more detailed observations of same object, perhaps at new wavelengths, with higher angular and temporal resolutions, accumulate longer baseline datasets, or examine other observable properties such as polarization of the photons;
- If the idea involves new atomic processes or particles, we can try to reproduce or detect them in controlled Earth-based experiments (i.e. Laboratory Astrophysics).
All knowledge is accumulated indirectly, even when conducted in laboratory equipment. The constituents of atoms have never been seen, only inferred from many experiments and observations. We construct mathematical models of these particles that can reliably reproduce measurements, both past and future.
I can't prove that we aren't all brains in a vat, providing biochemical energy for some supercomplex machine, and our 'reality' is just a very sophisticated VR program, such as in the movie, The Matrix.
There is no 'proof' of the theory of gravity. There is no 'proof' of quantum mechanics, nuclear physics, atomic physics, or any other science. There is only an overwhelming amount of physical evidence that it works. While they work today, tomorrow, we may have new experiments that hint at something beyond our 'standard models' of these phenomena.
Yet we build microelectronic circuits, nuclear reactors, and launch satellites into space and to other planets, using these 'unproven theories'. These same 'unproven theories', taken together, give us the great age (over 13 billion years) of the Universe. In spite of creationists' denials, these 'unproven theories' have made modern technologies possible.
So to those who wish to argue with me that astronomy is 'unproven' as a science, I insist that you provide me with PROOF, not just evidence, of the reality of electrons, protons, and neutrons. To make things more interesting, perhaps I should insist on PROOF that these subatomic particles are not, say, magical pixies that just happen to behave in ways we observe but which could change their behavior at any time. If you can't prove this, why are you using any microelectronics technology?
I'll close with an applicable quote:
Moreover, “fact“ does not mean “absolute certainty.“ The final proofs of logic and mathematics flow deductively from stated premises and achieve certainty only because they are not about the empirical world. Evolutionists make no claim for perpetual truth, though creationists often do (and then attack us for a style of argument that they themselves favor). In science, “fact“ can only mean “confirmed to such a degree that it would be perverse to withhold provisional assent.“ I suppose that apples might start to rise tomorrow, but the possibility does not merit equal time in physics classrooms. -- S.J. Gould, “Evolution as Fact and Theory”