A basic definition list.
is a piece of observed empirical data. This is subject to falsification, so the best data is of course that which can be verified. Generally, scientists tend to offer the benefit of the doubt to people who gather a piece of bad data, because the more sensitive the instrument, the greater the opportunity for errors, and they can come from weird places.
A scientific law
is, to put a banal description, a pattern observed in all available data that is, at worst, a good rule of thumb (This is an edit: MHaji
posted a better description below). Whereas a legal law is declared to get people to stop doing something, a scientific law is pointed out when they are adhered to.
Laws are, as a rule, rather simple and elegant. Someone mentions "The law of conservation of mass-energy", and further states the definition - mass and energy may be converted between each other, but never created or destroyed. They also get converted into pithy phrases a lot, like "You can't win, you can't break even, you can't leave the game" for thermodynamics.
Elegance does not always equate to having an easy time comprehending why. The speed of light is the same for all observers, everywhere, no matter how 'fast' they are moving. Worse, the number seems to be arbitrary (or more appropriately, the fine structure constant seems to be).
Laws are at the end of the day descriptions. They are not explanations.
A scientific hypothesis
is a testable
explanation for an observed phenomenon. The need for testing is key - if it can't be tested, it can't make predictions, and if it can't make predictions, it doesn't actually give us any additional tools to understand the world with. You can claim that God made the Universe in situ last Thursday. Your assertion cannot be disproven. However, your assertion has no predictive value, therefore we cannot draw conclusions based on it.
This distinction is important - you can't prove a scientific hypothesis or theory, only disprove it. This means that its value is entirely dependent on what it can teach.
A scientific theory
is a collection of one or more hypothesis that explain
a portion of our Universe. To be considered a part of 'scientific consensus', it needs to
1) Explain all previous data
2) Do so in the most concise manner possible
3) Make predictions about future observations that would be surprising without the enlightenment provided by the theory.
4) It should be conservative - staying within its realm and not making wild assertions."To explain all nature is too difficult a task for any one man or even for any one age. `Tis much better to do a little with certainty, and leave the rest for others hat come after you, than to explain all things."
- Isaac Newton
The Theory of Evolution says nothing of how life actually began, and an astute observer will note that Darwin wrote The Origin of Species
, not The Origin of Life
. He knew nothing of DNA, even though the most basic definition of evolution we now have requires its presence to even be understood - the change in allele frequency over time. That his theory has stood that test of time is a testament to his conservatism - he did not wildly speculate on how life began, just that life on Earth must have had a common origin.
Yet, despite that, it is still a bold claim. If it is wrong, then somewhere, somewhen, we certainly should have found a creature - a bacterium - somewhere in the world - with decidedly non-normal DNA. It makes a statement about what we should find when we look inside any and every cell native to our Earth, and should we find one single cell that is different, its presence will demand explanation.
Even when exceptions are found, just because a new theory replaces an older set of laws does not mean they fall out of use. We still teach that the Earth is round, even though we have a far superior understanding of the Earth's shape. When you calculate how long it is going to take you to drive home, you don't bother with relativistic modifiers.
Likewise, if Relativity and Quantum Mechanics break down under some ludicrous level of energy density, this does not mean we will stop using Relativity and QM in processor design. We might - I certainly don't know what form a unified theory would take - but it isn't given that it will be simpler.
On the other end of the spectrum, theories can sometimes have their processes observed from start to finish. You can take a microscope and watch germ cells invade a host, you can take a bacteria sample and direct their evolution. Germ theory and evolution remain theories, but these observations are facts, which means that any competing theory must also encompass the parts of the old theory that have been so directly observed. This can be a rather tall order if someone's sole goal is to just toss it on its head.
Something that I find a lot of people who object to 'science' misunderstand is that the sole, overriding goal of science is the discovery of Truth.
The scientific method, at its core, is about making observations, attempting to form hypothesis that make predictions, testing them appropriately, and repeat, until all of Truth is known.
And as Newton said, this is a task that is beyond the capacity of any one person. What we are learning today is the result of centuries of tests performed by our predecessors, and millions of people with the same simple goal.
There are two main points I want to express, here.
1) Yes, it really is that simple. Most of the difficulty people have in understanding things is coming to the realization that they can actually understand.
2) You are not going to understand everything. At the end of the day, you have to trust someone at some point in your life. You have to trust a lot of people in modern society. Making sure that trust is merited and failing to do so has consequences far beyond the realm of science.
Thank you for reading.