What We Now Know to Be True

Dr. Melik: This morning for breakfast he requested something called "wheat germ, organic honey, and tiger's milk."
Dr. Aragon: Oh, yes. Those are the charmed substances that some years ago were thought to contain life-preserving properties.
Dr. Melik: You mean there was no deep fat? No steak or cream pies or... hot fudge?
Dr. Aragon: Those were thought to be unhealthy, precisely the opposite of what we now know to be true.

Dr. Melik: Incredible.

—Sleeper

So you've got this great idea for a science fiction story. There's just one problem: an element of the story is blatantly contradicted by a piece of actual science, and you don't want it to look like you Did Not Do the Research.

But wait! Science Marches On, right? Science is always evolving, and sometimes what we thought was certain turns out to be incomplete or incorrect. So in a story involving people from the future, ahead-of-their-time scientists, or Sufficiently Advanced Aliens, one way of getting around a scientific inaccuracy is to mention the current theory... and then have one of the characters dismiss it as an outdated misconception.

This serves as a quick Lampshade Hanging which acknowledges the departure from the facts, and allows you to get on with the story. This kind of dialogue can also be used when the science itself is in a state of flux at the time of writing—the characters discuss the competing theories, and whichever one "was proven accurate" is the one taken as accurate in the story, whatever happens later in Real Life.

This trope can also be Played for Laughs, especially when the difference from real-world science is ludicrous: "People in the twenty-first century used to think that? They must have been really stupid!"

Compare Outgrown Such Silly Superstitions.

Examples of What We Now Know to Be True include:

Film

Played for Laughs in Woody Allen's Sleeper, as the quote at the top of this article would suggest.
- And ironically, modern research does suggest that steak (protein) is healthier than wheat germ (complex carbs.)
- Also he's urged to smoke and when he refuses "It's tobacco. It's one of the healthiest things for you."
The Manchurian Candidate mentions "that old wives' tale" that hypnotized people can't be forced to do things that are against their natures.
In the cheesy Queen of Outer Space movie, the four astronauts find themselves accidentally on an earthlike planet; examining its exact gravity level, they determine that they must be on Venus. The junior astronaut says, "What about all those lectures we got about Venus having an unbreathable atmosphere and a horribly high temperature?" The doctor says, "Yes, I formulated most of those theories myself. It seems I was wrong."

Literature

In Journey to the Center of the Earth, Axel expresses concern that the adventuring party will encounter great heat and pressure in the interior of the Earth, which will probably kill them. Professor Lidenbrock argues that the heat will not be great, and they will be able to acclimate to the pressure. He's right.
- In fact, this was a popular theory in the days of Jules Verne: that the only thing that happened as you get closer to the center of the earth is that pressure continued to increase, until you would eventually get to a point where the pressure was so great that the air itself was forced into solid form, representing the core. It was based on this theory that he wrote the story.
In Lucky Starr and the Oceans of Venus (written in 1954, before astronomers had a clear idea of what the surface of Venus was like), Lucky mentions that "until the late 1900s astronomers thought Venus had no water. When ships began to land, mankind found that wasn't so."
In a Discworld book, Vetinari comments how centuries ago they thought the Disc was round, but now it's a scientific fact it's a disc on the back of four elephants standing on a giant turtle.
The advanced aliens in the Uplift universe have nothing but contempt for the Earth concept of the continuum, and thus for any science not based on discrete mathematics. This may be justified, since even some contemporary Earthlings regard the continuum as a useful shortcut that we can forget about once we have sufficient computing power.
Atlas Shrugged: Galt's engine is called out as working on a new principle and proving several laws of physics to be false.
In one of the Animorphs books, the alien Ax is looking through the other Animorphs' text books and comments, "That's not how gravity works at all."
Many, many, many science fiction stories that have some form of Faster Than Light Travel will include some reference to (Scientist) who discovered the theory which superseded Relativity, and thus allowed faster than light travel.
Oddly enough, this sort of reasoning is sometimes used in actual science textbooks (usually when the writer themselves Did Not Do the Research and is just repeating the popular view). A good example is in biology where What We Now Know to Be True is that Pasteur "disproved" the theory of spontaneous generation. Actually, he didn't. Not conclusively anyway, and he hid some of his results according to the article.
Done in Call Me Joe, where Jupiter turns out to have a solid surface.

Live-Action TV

The Tollans, an advanced human civilization in Stargate SG-1, have studied quantum physics... "among other misconceptions of elementary science".
- Interestingly, this little revelation does nothing to show that quantum physics is wrong in the subsequent episodes and shows. Rodney McKay in Stargate Atlantis states that absolute clairvoyance is impossible, according to quantum physics. Apparently, he never met the Tollan. And he's supposed to be one of the smartest men on Earth.
  - What's worse, quantum mechanics have shown to be demonstrably true through practical applications in many, many episodes (pick any one that happens in a parallel universe, the first of which is all the way back in season 1 of SG-1, only a few episodes after the episode with the quote). Evidently either Narim was pulling a prank on Carter, or the Tollans have done a big mistake in dismissing the theory.
  - Or, more simply, quantum mechanics is incomplete in the same way that Newtonian physics is and fails to account for enormous divergences from its established system of logic.
Doctor Who, "Shada":

The Doctor: What? Do you understand Einstein?
Parsons: Yes.
The Doctor: What? And quantum theory?
Parsons: Yes.
The Doctor: What? And Planck?
Parsons: Yes.
The Doctor: What? And Newton?
Parsons: Yes.
The Doctor: What? And Schoenberg?
Parsons: Of course.
The Doctor: You've got a lot to unlearn.

Blake's 7 pulls a two-for-one example in the pilot episode, when the cast discover that their newly acquired spacecraft goes really, really fast:

Blake: You mean we crossed the antimatter interface? That's impossible.
Avon: That's what they said about the light barrier.

In an episode of the Outer Limits revival, some visitors from the future arrive and meet some present-day scientists. When the one of present-day researchers mentions time-dilation to a visitor she's chatting with, he winces a bit, although he doesn't correct her assumptions because he can't afford to change history by telling her where her ideas are wrong.

Web Comics

Played for Laughs in this Saturday Morning Breakfast Cereal strip.
Sailor Sun: "DNA is completely fictional."

Western Animation

Often played for laughs on Futurama:
- In "Mars University", Professor Farnsworth produces a hyperintelligent monkey:

Fry: Is he genetically engineered?
Professor: Oh please, that's preposterous science-fiction mumbo-jumbo. Guenther's intelligence actually lies in his electronium hat, which harnesses the power of sunspots to produce cognitive radiation.

- In "A Big Piece of Garbage", Mayor Poopenmayer refers to secondhand smoke and global warming as old, debunked hoaxes. Despite this a later episode was about how global warming was affecting the Earth when their temporary solution finally stopped working.
  - Although it's apparently still true that the Internet is just for looking at porn.