User:LBird BASc/sandbox/ATK/Seminar6/Evidence/Evidence in Physics

Evidence in Physics

Experimental Evidence

The historically typical model for supplying evidence for a theory in physics is known as the Scientific Method. Its first use is often credited to Aristotle "because of his refined analysis of logical implications contained in demonstrative discourse".This method essentially consists of an observation or a phenomena physical universe, a hypothesis of what the observer would expect to happen, a method of isolating said phenomena and testing the effects of it and then a rigorous comparison to the original model to determine if this model is supported by the evidence.

Summary of the Scientific Method

1. Formulation of a question in relation to a physical property of the universe: eg. Why do objects fall towards the ground?
2. Based on observation and often the evidence previously collected by other physicists form a hypothesis: eg. From Newton's Laws of Motion the acceleration required to move an object from rest must derive from a force (Newton's second law is Force=mass x acceleration). Perhaps this force comes from a Gravitational pull from the Earth?
3. You need to then form a theory of the logical consequences of the hypothesis. This is often demonstrated mathematically in order to get a quantitive value of how accurately the evidence supports the hypothesis. Eg. If the effects of air resistance and other forces can be negated, then one can work out a value of the exact time an object will take to fall a certain distance.
4. A prediction is then needed to compare to the results of the experiment. Eg. Work out how long the time to fall would be.
5. Testing is then required in the form of an experiment. To do this you need to conduct an experiment in such a way that other real world effects do not impact the results of the experiment, so it is necessary to isolate the individual effect or effects you are testing. Eg. Because the effect of air resistance on a falling object would result in an inaccurate value of the time taken to fall, you could negate the effect by conducting the experiment in a vacuum.
6. Quantitive Analysis is then required to determine if the results from the experiment do in fact support or or disagree with the calculated prediction. It is imperative to calculate the extent of uncertainty of your experiment to see if the results are significantly close to the expected value to suggest with a high degree of probability whether your results are accurate in their conclusions or not. Eg. if you were timing the fall time by hand and were only accurate to the nearest second, it might be possible that even if your results are as expected the uncertainty is significantly high to render your results inconclusive.

To What Extent is the Scientific Method Empiricist? (The rudiments of Philosophy of Science)

This method is an attempt to get as close as is possible to an empirical form of evidence to the theory and get a quantitive value of what degree the hypothesis is supported by the evidence. From the method though it is clear that this method is not totally quantitative due to the qualitative final conclusion. The conclusion of how the raw data relates to the prediction is always influenced by human opinion even if it is only the estimations of uncertainty in an otherwise qualitative method. In the experiment itself, due to the experiments being recorded by somewhat fallible equipment and human senses and judgement not being perfect it is logically impossible to get a perfect set of data. From both of these it is clear that totally empirical forms of evidence do not exist and although this is acknowledged by the use of uncertainties it is nonetheless important. Clearly this is very important when talking about scientific proofs, particularly in the media because there is often misconception in the meaning of scientific evidence.

When the Scientific Method is used successfully, it is also only demonstrating that the hypothesis matches the results in the single set of circumstances measured. When the hypothesis is deemed 'true' it is only through the logic of induction that it can be extended to the entire hypothesis. This means that it seems logically improbable that if it worked in this case, then it would not work in a similar one, but that is subtly different from the Hypothesis being true.

It is also essentially impossible to test a theory in isolation but I will explore a more obvious example of this when talking about Quantum Physics.

Quantum Physics

Without going into much detail there is a simple example from 'modern physics' to show a case where the Scientific Method of finding experimental data to support a hypothesis is totally impossible and physics must resort to a qualitative method of analysis most akin to Philosophy to explain it as determinism breaks down. The Heisenberg Uncertainty Principle states that it is impossible to know the position or the momentum of a particle beyond a certain degree of accuracy.

$\Delta x\Delta p=\hbar /2$

In this equation x denotes the position, p denotes the momentum and $\hbar$ denotes planck's constant (roughly 6.63x10^-34) divided by 2π. It is important to mention that $\hbar$/2 is a positive constant.

What this means for Physics is: in some cases (it is only really observable in results when the size of particles being observed are tiny, for example an electron) determinism totally doesn't work and you can't set an experiment, knowing the starting position and predicting the results. It is totally impossible to isolate certain properties of the particle in an experiment so the typical scientific method doesn't always work in the conventional sense.

There is also a Quantum effect observed in the Double Slit Experiment where particles such as electrons appear to behave like a wave by diffracting and interfering (properties of waves not particles), but when observing which slit the electrons pass through, they behave like particles. It is actually impossible to observe what causes this effect, as observing the experiment changes the result. This, for obvious reasons is difficult to explain using a purely scientific method of analysis, even though there is an essentially irrefutable amount of evidence, showing this effect occurs.