What is an example of a theory that everyone can understand?
In what context? Are you talking about scientific theories? In that case, there are many that everyone can understand at some level, not necessarily mathematically or technically, but enough to have a feel of.
For example, there’s the Big Bang Theory, which at its very simplest level is summed up by Wikipedia thusly:
I can think of several others, but it might help to know what you’re trying to get at before getting into more detail.
Most scientific theories can probably be understood by most people if only they put sufficient time and effort into it.
Whether it’s a theory as such, or not, it’s pretty easy to understand and accept the old proverb:
If a man is hungry, he will eat.
Gravity is a theory. We actually have no idea what it is but we have modeled it mathematically so can predict it.
Gravity itself is not a theory; it is an empirical observation about a physical phenomena. Now, we have “theories” about the behavior of gravity which can be–and have been–so thoroughly tested that they are considered nearly unassailable without remarkable evidence to the contrary. This makes the Newtonian, and later general relativistic models “laws”–that is, we have a model that predicts the behavior of gravitation that works as high a degree of precision as is possible to measure in every observed state (though the predictions of general relativity fall apart on very tiny scales at which fundamental particle interactions dominate). General relativity provides a very accurate model of how the presence of mass-energy distorts the plenum of space-time, and space-time causes mass-energy to move; however, it doesn’t explain what “space-time” is, other than describing it as a matrix upon which a momentum-energy tensor acts, which is like describing a movie in terms of light reflecting off of a reflective screen.
Natural selection is a theory that is so readily accessible and simplistic in its fundamentals and demonstrable in both models and practice that the only way to deny it is to concoct gymnastic arguments involving unseen supernatural beings manipulating biological processes from behind a large velvet curtain, or pick over the semantics of the language used to describe the phenomena (i.e. microevolution versus macroevolution). Even a cursory reading the popular science literature on the topic of evolution and natural selection reveals that despite all arguments advanced, they boil down to the same basic core set of fundamental principles based upon competitive preference and the conveyance of information from protein to protein via a transcription process that is used every day in forensic science, research pharmacology, and basic molecular biological.
Stranger
Do you mean everyone, like small children, or everyone, like high school educated non-mentally retarded adults?
Are you expecting them to understand it intuitively, or are we allowed to explain it to them and allow them to gain understanding by that?
Germ Theory is pretty simple, and even kids accept that germs cause illness (although they tend to accept it because they believe adults who tell them so). According to Koch’s Postulates, if we can find a microorganism in all of a group of sick individuals but not well ones, and we can extract that microorganism, grow it and then inject it into another not-sick individual who then gets the same illness, then we know the organism causes the illness.
Until we can actually *observe *germs causing illness (which we can’t), Germ Theory remains a theory. It’s not a Law, like gravity, but it’s a logical conclusion which has been borne out by repeated testing and provides us with a way to make predictions about who will get a particular illness and who won’t.
Gravity is too a theory, or, at any rate, it is a theoretical notion. The relevant empirical observation is merely that things tend to fall down (except for things, like fire, that don’t). The theory that this tendency is due to an invisible force pulling things toward the Earth did not occur to anyone throughout thousands of years of human history until Isaac Newton articulated it, and gave the name “gravity” to this force. (Before Newton, the word “gravity” had just meant something like “heaviness”.) Indeed, I would submit that this conceptual innovation of Newton’s was much deeper and more significant contribution to our understanding of the world than was the mathematical description he also gave of the quantitative operation of the gravity that he had invented.
Gravity today only looks like a plain empirical fact, or the “natural” way of thinking about the phenomena, because just about everyone in our culture learns about the theory of gravity (at a qualitative level, without the mathematical trappings) at a very early age, and becomes so used to thinking about things falling down in terms of a pulling force, that it I becomes hard to imagine that anyone ever thought about it otherwise. In fact, however, they did. The smartest, most educated and most enquiring minds thought about the phenomenon of falling down otherwise (in at least two or three other ways, in fact) over the millennia of recorded human history.
I would suggest, then, that the theory of gravity (in its more fundamental, qualitative aspect) is indeed a theory that “anyone” can, and, indeed, generally does, understand.
Nah. Terry Pratchett said it more simply: “In the beginning there was nothing, which exploded.”
There’s Boyo Jim’s Theory of Hotness:
I have elevated it to “theory” level because if people are exposed to images of women I consider hot, they can reliably predict which other women I perceive to be hot.
I don’t understand it.
I mean, I know it’s the reason we don’t fly off the ground, but I don’t begin to grok why or how it works or what it is (if it’s even an “it”).
Theories don’t explain the “why” about anything. Some theories, but not all, explain the “how”. Many theories just explain the “what”, as in “what will happen in particular circumstances under specified conditions”.
A hypothesis is a statement that makes a testable prediction.
A theory is a hypothesis that has been well-tested.
Forming hypotheses, and testing them isn’t just how we conduct science, it’s how we conduct our day-to-day lives.
For example, say you’re sitting at home and you hear the garage door open. You form the hypothesis that your girlfriend has returned from the grocery store. You glance out the window and see the back end of her car as it disappears into the garage. Now you have experimental confirmation that your hypothesis was correct. It’s promoted to the status of a theory. You don’t have absolute proof that your “girlfriend is home” theory is correct, but you do have some pretty strong evidence to support it.
Then you hear her voice in the garage. Then you hear the door open. Then she walks in the living room and says “hi”. Each new data point increases your confidence in your “girlfriend is home” theory. The testable predictions of your original hypothesis are being repeatedly confirmed.
And yet, you never reach the point where you can be absolutely certain that your girlfriend is home. Maybe she was secretly replaced by an exact duplicate at the store as part of some diabolical plot. Maybe she has an identical twin and they’re playing an elaborate prank on you. Maybe you’re asleep and you’ve only dreamed that she came home. And so on. The more you observe your girlfriend after she returns from the store, the more certain you become that your “girlfriend is home” theory is correct, but there’s always a tiny lingering possibility that you’re mistaken.
That’s exactly how theories in science work. The only difference is that scientists are more rigorous in how they go about testing predictions.
Some of the basic mathematical principles should meet the OP’s request.
For example, commutative theory of addition: that 2 + 4 has the same answer as 4 + 2. Just about everybody past 3rd grade can understand that.
That is not a theory in the scientific sense, or even a theory in any sense that I can immediately think of. I have never heard of described as a ‘theory’ of addition, but rather as a property of addition.
The word “theory” is used in mathematics in a slightly different way from how it is used in the empirical sciences. E.g., number theory, group theory, graph theory, game theory, probability theory, set theory, category theory, model theory, …
I suspect some of the basic “laws” would suffice. The most basic, and readily grasped are the conservation laws.
For instance a simple one that is taught to young children is conservation of volume. (Jars of different shapes with the same volume and pouring water from one to another.)
Once you get conservation of volume is isn’t hard to start on mass, momentum, angular momentum. Conservation of energy is another step, although the concept of energy requires a reasonable amount of legwork to get straight.
Indeed the conservation laws underpin so much, and are in principle so simple, that I would really hope any ordinary person can grasp at least the classical versions.
This is entirely wrong, and entirely not your fault. Schools should stop using those words unless and until they can use them correctly.
A theory is an explanation that allows us to make predictions. A law is a mathematical equation that allows us to describe and predict a situation in numerical terms. That’s it. Every other explanation is wrong.
Theories do not become laws any more than novels grow up to become epic poetry. It doesn’t work that way except in grade school ‘science’ class, where very little science is actually taught.
Conservation of volume? Never heard of that one.
Conservation of volume of a liquid. OK, not a proper physical law, but clearly a derived idea. Liquid occupies the same volume irrespective of the shape of the vessel. That is a good theory that most people would cope with. Indeed psychologists use it as a marker in cognition development.