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What is the Difference Between a Theory and a Hypothesis?

By R. Kayne
Updated May 21, 2024
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A hypothesis attempts to answer questions by putting forth a plausible explanation that has yet to be rigorously tested. A theory, on the other hand, has already undergone extensive testing by various scientists and is generally accepted as being an accurate explanation of an observation. This doesn’t mean the theory is correct; only that current testing has not yet been able to disprove it, and the evidence as it is understood, appears to support it.

A theory will often start out as a hypothesis -- an educated guess to explain observable phenomenon. The scientist will attempt to poke holes in his or her hypothesis. If it survives the applied methodologies of science, it begins to take on the significance of a theory to the scientist. The next step is to present the findings to the scientific community for further, independent testing. The more a hypothesis is tested and holds up, the better accepted it becomes as a theory.

The theory of evolution, for example, is supported by a plethora of scientific evidence in the form of cosmological, geophysical and archaeological research data, to name just a few relevant fields. Scientists have not only traced the evolution of species through skeletal records, but the earth itself, our solar system, the stars and galaxies can be “dated” through various scientific methods. This evidence appears to track the universe back about 13.7 billion years to a “Big Bang” event.

While there appears to be no end to the evidence supporting the theory of evolution, it is still only a theory. Theories, no matter how well accepted, are always subject to change as new knowledge comes to light. Einstein’s Theory of Relativity, for example, explained the world on a massive scale, but broke down when it came to the world of the infinitesimally small. This famous theory was augmented more recently by superstringsM-theory, which very nicely united the four known forces in the universe in one elegant mathematical equation. M-theory exotically predicts we live in a world of ten dimensions, plus one for time, for a total of 11 dimensions. While many aspects of M-theory make it difficult to test, the mathematical perfection of this theory has lent it strength in scientific circles.

A current hypothesis of great importance is that of dark energy. Scientists can calculate how much mass is present in the universe, yet physical matter – matter made from atoms – makes up only four percent of the total. Dark matter is believed to make up another twenty percent, leaving about seventy-six percent unaccounted for. Enter the hypothetically summoned dark energy to fill the gap. There are a few competing candidates for dark energy with research underway. However, one of the problems is difficulty in detecting it. So even while its interaction with gravity on a massive scale is sufficient to cause the universe to rapidly expand outwards, in the lab detecting it is a bit like checking for a light breeze using a weathervane full of gigantic holes. Nevertheless, as scientists untangle the mystery of the missing mass, the answer will one day rise from mere hypothesis to generally accepted theory.

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Discussion Comments
By anon347404 — On Sep 06, 2013

Hypotheses can never become theories. They are separate things. There is no hierarchy.

By anon287626 — On Aug 26, 2012

To anon65339 and anon91831: You're both obviously logical, scientifically minded, free-thinking people.

However, whoever wrote this article is obviously not.

I would imagine that s/he is probably just another Darwinist member of the 'scientific' community, pushing the official belief-system.

By anon254321 — On Mar 12, 2012

I do not agree with this article.

A theory means a model. Evolution has nothing to do with the big bang or with Abiogenesis.

This is the kind of confusion I would expect from a creationist.

By anon117205 — On Oct 09, 2010

There are two parts to evolution. There is the fact of evolution, namely that there occurs heritable changes in the gene pool of a population over time. This is irrefutable and can be simply demonstrated. To deny this part of evolution would be like asserting that the earth is flat.

The second portion is what most people think of as the theory of evolution. The theory is based on the fact of evolution and attempts to explain the relative importance of different mechanisms of evolution such as mutations, genetic drift, migration and natural selection. Hope this helps.

By anon100627 — On Jul 30, 2010

If a hypothesis and theory are different, then why are they considered synonyms in dictionaries?

Also: This site is the first I came across, where it says Dark Energy is a hypothesis, where the science channel, sometimes discovery channel, and their websites all say it's a theory?

By anon91831 — On Jun 24, 2010

There is no cosmological evidence for the theory of evolution.

The theory of evolution is about the origin of species, not about the formation of the universe.

By anon91615 — On Jun 22, 2010

All theories are based upon other theories. At the core of all science there must always be some assumptions.

For string theory it rests on basic theories of quantum mechanics and theories about the functioning of gravity.

For evolution there's a basis in chemical theories and physical theories.

All theories are constantly open to modification and even outright dismissal. As an example, it wasn't until at least the 1980s that horizontal gene transfer began to be part of the theory of evolution.

By anon80190 — On Apr 26, 2010

string theory is really, a hypothesis. evolutionary theory, however, is not. there is a plethora of molecular evidence for evolution that is not merely fossil record.

fossil record is cute, but protein and mitochondrial DNA sequences don't lie. A good example is the "mitochondrial distance". You can compute this distance between any two eukaryotic species.

between you and say, your cousin, or a monkey or a naked mole-rat. And they show precisely what you would expect.

For example, george burns was related more closely to the naked mole-rat and george bush was more closely related to the monkey than my cousin. etcetera

By anon65339 — On Feb 12, 2010

The problem with the "theory" of evolution is that all the evidences are based on assumptions--it cannot be tested. There is a huge difference between observable science and historical science since the former is repeatable while the latter can not.

"Scientists have not only traced the evolution of species through skeletal records..." is historical science since there is nothing to tie that one set of skeletons is related to another.

"...the stars and galaxies can be 'dated' through various scientific methods." Even this author uses "dated" in quotes, reinforcing that this is not observable science and an assumption.

"This evidence appears to track the universe back about 13.7 billion years to a 'Big Bang' event." Even though the stars and galaxies can be shown to move at a certain rate, it is still an assumption that that rate has been constant. What we observe today tells us only that this is how they are moving today, and nothing about how they did move.

Really, it should be call the "Hypothesis of Evolution".

By anon39249 — On Jul 31, 2009

The others who commented are under the misconception that "testing" only refers to physical experiment. If a theory is expressable mathematically, it is tesatable in the sense of mathematical proofs (consider it a mental test of a hypothesis). If the hypothesis survives numerous, rigorous mathematical "tests", it is a theory where each test is very real, supporting evidence of its accuracy.

By anon36858 — On Jul 15, 2009

I agree. In fact, any version of string "theory", due to the inability to test, perhaps is merely a conjecture.

By anon33960 — On Jun 15, 2009

It seems the stated difference between a hypothesis and a theory is then contradicted by calling string theory (M or otherwise) a "theory." Since at present it is impossible to test, mathematical elegance aside, is it not simply a hypothesis?

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