[Leaning Right]

There is a principle in physics, called the Principle of Self-Consistency. This principle states that if you could go back in time (by whatever method), you would not be able to change anything.

In other words, what has happened cannot be changed.

For example, penicillin was discovered in 1928. You cannot go back in time and discover it in 1015. Every attempt you make to discover it in 1015 must fail.

[Buttons12]

I forget the particulars, but someone noticed the value of penicillin before 1928. Aside from him, there were some folks in North Africa who used a form of it, if I recall, they had it growing on saddles and knew it was useful to help heal wounds.

Anyway...who wants to go back in time? You’re likely to be mistaken for a lunatic or a witch.

[Talisker]

There is a principle in physics, called the Principle of Self-Consistency. This principle states that if you could go back in time (by whatever method), you would not be able to change anything. In other words, what has happened cannot be changed.

That principle's only consistent in a world where people cannot go back in time - by definition. But if someone actually did go back in time, then the reality of that ability would mean a world where time travel was possible. And in that case, only experimentation could resolve whether history could be changed.

[Ellendra]

There is a principle in physics, called the Principle of Self-Consistency. This principle states that if you could go back in time (by whatever method), you would not be able to change anything.

How many times has this principle been tested?

[Buttons12]

Looked it up. In the 1890’s, French physician Ernest Duchesne noticed that penicillium mold inhibited germ growth, but he was ignored.

[Smokin' Joe]

You cannot go back in time and discover it in 1015. Every attempt you make to discover it in 1015 must fail.

Meh. Perhaps not fail, but become another 'lost' art...

For all we know, penicillin has been used many times before, but the knowledge of it failed to survive the ages.

[Joe 6-pack]

"There is a principle in physics, called the Principle of Self-Consistency. This principle states that if you could go back in time (by whatever method), you would not be able to change anything."

Which would itself create a paradox, because a person with an in depth, detailed knowledge of history would distinguish himself as a great seer or prophet of the, 'future'. i.e. imagine showing up at the US War Department on Friday, December 5, 1941. People might not take you seriously that day, but would probably want to talk with you at length the following Monday.