Some of these are probably apocryphal, but making predictions about the limits of technology is really hard:

Space travel is utter bilge.

Computers in the future may...perhaps only weigh 1.5 tons.

- Popular Mechanics, 1949

X-rays are a hoax.

- Lord Kelvin, ca. 1900

I confess that in 1901 I said to my brother Orville that man would not fly for fifty years. Two years later we ourselves made flights. This demonstration of my impotence as a prophet gave me such a shock that ever since I have distrusted myself and avoided all predictions.

To place a man in a multi-stage rocket and project him into the controlling gravitational field of the moon where the passengers can make scientific observations, perhaps land alive, and then return to earth--all that constitutes a wild dream worthy of Jules Verne. I am bold enough to say that such a man-made voyage will never occur regardless of all future advances.

- Lee deForest, inventor of the vacuum tube, 1957

There is not the slightest indication that [nuclear energy] will ever be obtainable. It would mean that the atom would have to be shattered at will.

- Albert Einstein, 1932

That is the biggest fool thing we have ever done. The bomb will never go off, and I speak as an expert in explosives.

Anyone who expects a source of power from the transformation of these atoms is talking moonshine.

- Ernest Rutherford, 1933

The abolishment of pain in surgery is a chimera. It is absurd to go on seeking it... Knife and pain are two words in surgery that must forever be associated in the consciousness of the patient.

- Dr. Alfred Velpeaum, French surgeon, 1839

Bitcoin is definitely going to be trading at $10,000 or more and in wide use by the end of 2014.

- Many otherwise smart people, November of 2013

Superhuman machine intelligence is prima facie ridiculous.

- Many otherwise smart people, 2015

(Most of these from: https://www.lhup.edu/~dsimanek/neverwrk.htm)

