You are on a speeding train-- high school physics.

[Hampshire]

Seeing that the earth is being flung through the universe at thousands of mph, I pity the poor sap who invents the first time machine and goes back 50 years only to find himself floating in the middle of nowhere.

[Boyo_Jim]

1Maybe not – maybe in the middle of the sun

[cmyk]

@njtt

Is there any actual dictum involved here? The page you link to, despite its title, contains nothing by way of a dictum, and Googling “Galileo’s Dictum” comes up with little more than that page, this thread, and references to other, actual but unrelated, dicta of Galileo.

I will grant you that Galileo was the first to clearly express the relevant insight into the nature of motion, but did he ever express the point in a pithy or aphoristic way that might appropriately be called a dictum? I remain to be convinced.

Y’know, I’ve never really given it much thought. I first read about his relativity principle in some old book when I was in my teens. I have no idea what that book was, but it was your general physics written for the layman sort of book, and the author called it Galileo’s Dictum. I guess that term just always stuck with me. I’ve heard it called his principle of relativity as well, but that’s a mouthful.

[cmyk]

After some more googling, I think I found the source where I first read of it; from this book: Essays on Galileo and the History and Philosophy of Science, Vol 1, by Stillman Drake, Noel M. Swerdlow, and Trevor Harvey Levere.

@Essays on Galileo and the History and Philosophy of Science

Medieval speculations on motion, far from accounting for the actual introduction of the inertial concept, only make it hard to see why the idea did not appear two or three centuries earlier, as a philosophical extension of earlier projectile motions. The idea took form in Galileo’s mind, not among philosophers or society as a whole; and it met with opposition at first from representative philosophers familiar with earlier speculations. Aristotle’s dictum that nothing violent could long persist lay at the basis of that opposition, and the dictum can explain the failure of the inertial concept to appear so long as respect for authority dominated physical thought.

So, in this light, the term 'dictum", may in fact had been applied to his principle by his opponents and dismissed it as a Simplex Dictum: an unproved or dogmatic statement. Since in his day, he was trying to turn over the more authoritative philosophical attitude stuck on Aristotle’s brand of physics.

My WAG anyway.

[Mangetout]

@Hampshire

Seeing that the earth is being flung through the universe at thousands of mph, I pity the poor sap who invents the first time machine and goes back 50 years only to find himself floating in the middle of nowhere.

But how would that work, when there’s no absolute frame of reference?

[Asympotically_fat]

@Mangetout

But how would that work, when there’s no absolute frame of reference?

I think it’s well established that time machines will return you to the same coordinates in the Earth-centred Earth-fixed coordinates[sup]1,2,3[/sup]