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Comment by ctoth | Hacker News Reader

"Heavier-than-air flying machines are impossible." -- Lord William Thomson Kelvin, British mathematician and physicist, president of the British Royal Society, 1895.

Edit: See https://news.ycombinator.com/item?id=27816225 for a discussion of the paper that launched this whole topic.

Edit 2: The actual paper you want is this one by the author of OP, the first one is referring back to this: https://arxiv.org/abs/2006.07125

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Scientifically speaking, the fact that someone was wrong in the past, doesn't mean someone else is wrong now, even if they use a similar sentence structure.

PS Yes, I am fun at parties, if I ever get invited to one again!

You're technically correct but missing the point. Past hubris is a warning that we are capable of similar hubris.

What we can say is our current model of the universe does not allow for any practical travel beyond the speed of light.

Valid warnings also don't mean anything.

We can also say that our current model of the universe is orders of magnitude more accurate, so it's more likely that we're correct about the speed of light - something which has been experimentally tested and verified by hundreds if not thousands of people - than the opinion of one particular Lord Kelvin regarding the viability of aircraft.

It's just as hubristic to assume that science is as ignorant now as it always has been.

Yes but we do have theories that suggest getting from point A to point B faster than light could be possible. We just have to do some things that appear impractical such as bend spacetime.

If FTL were possible, don’t you think there’d already be evidence of the time travel? First thing I’d do with FTL is travel back to the earliest habitable epoch in the Universe and start building galaxy-sized Dyson spheres.

Can you elaborate please.

Why does FTL produce time travel?

Why go back and build Dyson spheres?

In special relativity, faster-than-light travel or communication is equivalent to time travel.

Yes but that is only if you are traveling through space faster than light. If you simply skip some of the distance with something like an Alcubierre drive there is no time dilation to deal with.

No, it still results in time travel.

> To answer your question: any FTL drive can be used to create closed time-like loops. With these you can travel back in time, but you get stuck in a loop.

https://physics.stackexchange.com/a/247048

Okay, I think there is something I don't understand here. That link references a book I might have to read "Time Travel and Warp Drives".

Thanks!

> simply skip some of the distance

My understanding as a lay person of the physics that allow for things like this, is that they require starting conditions that wouldn't produce a universe anything like what we actually live in, or require energy levels around the output of galaxy superclusters to be focused into planck lengths or such. "Technically not impossible" is different for physicists than to normal people ;-)

But, it doesn't enable time travel. It just makes calculation easier, like «bending» of space-time array.

If you switch from relativity to regular physics with medium instead of pure vacuum (10 years passed since 2012 already, so relativity is busted at this point), then c is the speed of light in medium, so we don't need to bend anything or use negative t to calculate outcomes.

> so relativity is busted at this point

Excuse me?

To answer the second question, so that I can be the bad guys from the end of that Cixin Liu trilogy. Exponential growth is infinite and resources are not, so take any available advantage.

Short answer to the first, because the speed of light is the top speed at which information can propagate in the Universe.

Thank you another book/trilogy to add to the reading list.

I suggest you also add The Wandering Earth by the same author to your list, which is a collection eleven of his short fiction stories. I'd even go as far as say it's better to read it first before the trilogy.

You’re welcome! Incidentally, there’s no FTL in the story.

I don't think a gold standard is a viable pyramid scheme for a multiplanetary species. There's too much of it in space. You need something that is rare even after traveling for hundreds of years. A lot of wars were simply fought over resources. It's even better if your society uses the resource as money. The only thing I can imagine is using habitable planets as currency, this would require your galactic empire to have a dozen planets though because a single planet does not make a currency and the debt trap of borrowing 1 planet at 3% interest would fall apart because colonizing the next planet may take too long to pay off the interest. I.e. you need some planets to lose before you take that loan.

Edit: Great filter hypothesis to explain Fermis paradox. The pyramid scheme needed to enslave the galaxy is also powerful enough to destroy a planet before it develops space faring technology.

Just to point out obvious, you are applying a human logic to an theoretical alien species of theoretically any type of behaviour/value/technological/political angle.

Who knows what they are like and what they value.

Those theories would still result in time travel becoming possible and all the assorted paradoxes that come with it.

Which ignored the obvious and prevalent heavier-than-air flying birds. We have no such examples to point at with FTL travel.

"Inertia is a property of matter" - fundamental unchangeable property of the universe

...so far.

What about perpetual motion machines though? :)

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