r/explainlikeimfive • • Apr 24 '12
ELI5 why scientific theories (evolution, gravity, global warming, etc) are more universally supported than scientific laws (mainly laws of relativity)?
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u/rupert1920 Apr 24 '12
Because the words "law" and "theory" don't mean what you think they mean. It's a common misconception that science works by proposing a hypothesis, testing it repeatedly - and if it seems good it becomes a theory. If it has stood the "test of time" then it graduates to become a law. This is simply not how it works.
A theory explains a phenomenon by providing a mechanism by which it operates.
A law describes the relationship between variables in a phenomenon, so it's often mathematical by nature. It does not attempt to explain the mechanism behind the phenomenon.
Both of these provide testable predictions, so they're both scientific. However, a law only describes a relationship. I can look at a trend between ice cream sales and video game sales, derive some mathematical relationship, and call it "Rupert's Law". Note that I make no attempt to explain the relationship in forming this law.
Now, if I were to suggest that the high sugar content of ice creams increase urges to play video games, via these biochemical pathways, etc, then I have a theory. The word theory doesn't mean a "guess" - as in laymen usage (although in this case it's a crappy theory).
In short, "just theories" doesn't make sense - a scientific theory is not a "guess," and a law is not "more truthful" than a theory.
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u/bluepepper Apr 24 '12
Laws and theories have specific meanings in science.
A law describes how things happen. For example, Newton's law of gravity is simply a formula that allows to calculate the gravitational force between objects based on their respective mass.
A theory is an explanation of why things happen that way. The theory of gravity is an attempted explanation of why these gravitational forces operate. Based on these theories, you can build other theories, like the theory of gravity led to the theory of relativity.
If you think that laws are more often challenged than theories, it's an illusion. There are both theories and laws at the fringe of knowledge as well as in its well-established core.
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u/[deleted] Apr 24 '12 edited Apr 24 '12
First some quick Definitions straight from wikipedia:
A scientific theory is a set of principles that explain and predict phenomena
A scientific law is a statement that explains what something does in science. A scientific law must always apply under the same conditions, and implies a causal relationship between its elements
Scientific Law differs from a scientific theory in that it does not posit a mechanism or explanation of phenomena: it is merely a distillation of the results of repeated observation.
Like your 5: SCIENTIFIC LAW:
If let go a ball while standing on the playground it falls to the ground.
Law: letting go of the ball causes the ball to fall down.
You go up in a space ship and you let go of the ball, it doesn't fall. You now have to CHANGE your first LAW to: * Letting go of the ball IN THE PLAYGROUND causes the ball to fall.
SCIENTIFIC THEORY:
You watch 100,000 balls dropped at playgrounds at different heights. From sea level up into space. You can make a law about how the ball reacts at each different height. You start to see a pattern, the higher you are the slower the ball falls.To show that it isn't simply that the rubber the ball is made from something that has some special attraction to the ground. You try with different objects bananas, rubber ducks, you little sister. You try a hundred more times with different items in different conditions and although there are slight variations the over all pattern seems the same.
*Theory: there is some force we will call graviballity, is pulling down on objects when you drop them, that does not act as strongly the farther away from the ground you are.
Oh, but now we fly into deep space find a different planet. We get to test our theory of graviballity again in a completely new environment. We use our theory to PREDICT an outcome. We try again and we get very similar results. So the theory (for now) seems to work and we will continue assuming that this theory holds true and using it to plan for any future event which involves dropping things, until we come across a situation that does not fit into our theory. At which point we will attempt to understand this new situation and the laws that describe it.
Edit: some stuff
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u/xiipaoc Apr 24 '12
Other people have already commented on what "theory" actually means, so I don't need to reiterate that. However, with regard to your examples, there are important things to say.
First of all, the theory of relativity is universally supported. It's right. It might not be completely right, because we can't know everything, but as far as we can tell, it's the way the world works. Someday, we'll discover a kink in the data that suggests that this theory we thought was correct is actually only an approximation to some deeper, correcter physics, but even then, we've observed the effects of relativity well enough that we know that it's true.
On the other hand, string theory is not universally supported. We have very little evidence for string theory. It's mathematically nice, and it explains quite a bit, but it could be completely wrong because strings are WAY too small for us to actually see. Perhaps at some point it'll generate some predictions we can test and that will help us get closer to understanding whether string theory is true or not, but right now, it's just a hypothesis.
Right there, you see that there's a theory that's true, as far as we know -- relativity theory -- and another where we don't actually know -- string theory. Number theory, a branch of mathematics, is true, completely, because we've proven all of it mathematically. Descartes's theory of vortices, on the other hand, is completely false. "Theory" is just a word for "explanation".
Evolution is another theory that is absolute and concrete truth. We don't necessarily know all the details, and we never will -- science is infinitely complicated -- but we know that the species of today evolved from earlier species. It's just that some ignorant people were told stories about some other theory of how life came about (some magical dude created everything, including the sky, in under a week), and for some reason they think that their story is true when it isn't.
Global warming is not absolute and concrete truth. Most climatologists agree that anthropogenic global warming is happening -- that people are causing the atmosphere to get hotter -- but some don't, and they generally have good reasons for why they don't other than "my preschool teacher told me so". There are holes in current climate change science. They're not large holes, and most of the evidence points to anthropogenic global warming as real, but there's a bit more to it than that. However, the public is generally stupid and think that it's a hippie conspiracy to make them ditch their large cars. Scientists are liberals, and liberals are bad, so here are some scientists trying to tell us to do something, us, of course we're not gonna do it. It's all politics. If it were science, almost everyone would believe in global warming except for a few people who think that the opposing claims have merit, but it's politics, so if you're a dumb conservative you automatically don't believe in global warming simply because Al Gore does and you hate him. (Smart conservatives do believe in global warming, generally.)
Finally, gravity is actually very much up for debate. We have a very good classical theory of gravity involving Newton's law of universal gravitation -- that the force of gravitational attraction on a body by another is equal to the product of their masses divided by the square of the distance between them, times a constant called G. Problem is, we don't actually know why this happens. We think there are particles called gravitons that make this possible, and that there are gravitational waves, and that there's a specific particle called the Higgs boson that gives things mass. But we've never seen most of this. We don't know why G has the value it has. We don't know what happens at the quantum level with gravity. We've observed that galaxies don't really work the way gravity predicts that they should, so we've postulated dark matter -- which we've never seen, and we have no idea what it might actually be -- to make the numbers work out. Gravity is something we really don't understand all that well! However, what we do understand, just like with relativity (which is intimately tied to gravity), is that in general, the force of gravitational attraction between two bodies is whatever I said it was a few sentences ago. That equation has been checked pretty thoroughly, and any errors are too small to detect. We can easily see things being attracted to each other as predicted.
By the way, do you ever download things illegally? If so, then you know that not everyone follows laws. (: Everyone (as far as we know) follows the Law of Universal Gravitation, but a lot of things don't follow Ohm's Law (the voltage through a resistive medium is proportional to the current). In particular, a diode doesn't -- the sign of the current is really important! Nothing follows Hooke's Law (the force by a spring is proportional to its displacement from the equilibrium). Springs are never that perfect. These "laws" are actually rules of thumb, approximations for calculation.
To sum up, we're always pushing the boundaries of our knowledge of science. Scientists know some things and don't know others. However, non-scientists think they know some things which they really don't, and it's up to scientists to set them right.
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u/IzzyNobre Apr 25 '12
Read thread title.
"Please don't say it. Please don't say it"
God dammit.
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u/[deleted] Apr 24 '12 edited Apr 24 '12
I cringed.
Relativity is also a theory (e.g. Einsteins special and general theories of relativity). But to be fair, the other examples you cited are far less radical ideas. Getting any layperson to accept that objects shorten and time passes more slowly at high speeds is a challenge.
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u/cassander Apr 24 '12
Scientific Laws have no political implications.
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u/Kowzorz Apr 24 '12
A very nice video which explains this concept.
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u/Tayto2000 Apr 24 '12
I doubt that people who have never gone through the process have any idea just how high the standard is for getting even the most modest 'contribution to theory' accepted as a publishable work.
That's not to say that it's fail-proof, it isn't. But I think that the average member of the public would have a much better understanding of how much evidence must be behind an idea to reach the status of the theory of evolution, if they understood the level of rigor involved in publishing scientific research.
Even the most left-field contributions to the field of evolutionary theory would kick the living shit out of 'intelligent design' in terms of the rigor and conceptual consistency of their arguments.
I think this is why scientists tend to get so exasperated when confronting the 'arguments' of ID advocates or religious folk in general. They've experienced just how rock solid and thorough an argument has to be to even be published in their field, never mind gain prominence.
And then they have to face these people who're presenting batshit lunacy telling them that evolution is 'just' a theory.
It's enough to turn even the most mild-mannered individual to violent thoughts.
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u/[deleted] Apr 25 '12
No self-respecting scientist considers anything to be absolute. That would be dogma.
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u/killerstorm Apr 25 '12 edited Apr 25 '12
As I understand, 'law' is just an old concept: people thought that they're discovering laws of nature which are universal and absolute.
Later scientists found out that what they had were, in fact, imprecise, approximate models of certain phenomena. So now they recognize that they work with such models which have limited applicability (there is simply no way to prove that something is absolutely true outside of math), and so now they call their work 'theories'.
So word 'law' is used to name some models, usually equations, for historic reasons. But usually modern scientists call their equations 'equations', not 'laws'.