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Time is a dimension, but not like space

(bigthink.com)
171 points belter | 1 comments | 17 Oct 24 15:29 UTC | HN request time: 0.205s | source
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nyc111 ◴[20 Oct 24 04:27 UTC] No.41892855[source]▶
"This is the underlying reason why, when you move at speeds that approach the speed of light, you start to experience phenomena such as time dilation and length contraction:"

This is not even possible in pulp science fiction. In order to be able to move with the speed of light you need to transform yourself into a photon. Only a photon can move with the speed of light. Saying "close to the speed of light" changes nothing. You need to be light to move with the speed close to the speed of light. Macroscopic objects cannot move with speeds approaching light speed.

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nyc111 ◴[20 Oct 24 08:09 UTC] No.41893781[source]▶
I guess you guys found a way to accelerate human body to the speed of light without disintegrating. Why don't you prove your technique first with G-forces?
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itishappy ◴[20 Oct 24 16:40 UTC] No.41896584[source]▶
Why don't you? Here's a calculator:

https://gregsspacecalculations.blogspot.com/p/blog-page.html

1G of acceleration (which I'd hope you agree is survivable by humans) over an extended time period can easily reach relativistic speeds.

    1 day   .0028c
    1 week  .02c
    1 month .086c
    1 year  .77c
    2 years .97c
    3 years .996c
    4 years .9995c
    5 years .9999c
The thing stopping us from doing this today is economics, not physics. Current rockets have about enough fuel for minutes of acceleration, and fuel requirements increase exponentially due to the tyranny of the rocket equation. If you skip the need for fuel (laser propulsion?) and find some way to decelerate (laser cooling propulsion???), then interstellar travel to pretty much anywhere becomes entirely reasonable within human lifespans.

https://en.wikipedia.org/wiki/File:Roundtriptimes.png

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shiroiushi ◴[21 Oct 24 08:27 UTC] No.41901905[source]▶
I think you're handwaving away the other issues with physics that make near-lightspeed travel effectively impossible for humans. How exactly do you propose sustaining 1g acceleration for 5 years, for instance? You can't just "skip the need for fuel". Lasers aren't perfectly collimated and spread out over distance. Even an Epstein drive from The Expanse will eventually run out of fuel. The other big problem is: how exactly do you deal with collisions with space debris? Even at the speeds we currently travel, micrometeorites are a problem, but at 0.9999c, even stray hydrogen atoms (which deep space is full of) are going to destroy your ship.

Honestly, Star Trek way back in the 1960s was pretty brilliant at getting around many of these technical problems by inventing "warp drive".

Even if we somehow magically solved our economic problems overnight, that isn't going to make relativistic speeds feasible for humans anytime soon, if ever.

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1. itishappy ◴[21 Oct 24 14:04 UTC] No.41904295[source]▶
I'm definitely handwaving away the difficulty, but I did explicitly speak to these concerns.

We really can skip the need for fuel, for example. Sails (with or without lasers) are a technology we have proven in the field. Lasers do lose collimation over distance, but you can reach relativistic speeds before then (I'd argue that .02c from 1wk of 1G is relativistic). That won't get you to the center of the galaxy (or solve the deceleration issue), but there are proposals being reviewed today to use lasers to send probes for a flyby of Proxima Centauri.

https://www.nasa.gov/general/swarming-proxima-centauri/

https://en.wikipedia.org/wiki/Breakthrough_Starshot

But we don't need science fiction tech for this to work, we just need impractical amounts of fuel. Starship only has enough fuel to last 10m? Just send 50k starships and you can burn for a year. Tyranny of the rocket equation requires additional fuel to push all that fuel? Just send another billion Starships or whatever. Going too fast and now the interstellar medium hits like high-energy cosmic rays? Just send more shielding and fuel. This assumes we can build and fuel billions of Starships, which is certainly infeasible, but I'm calling this an economics issue as we have these technologies today.

If we want to get really sci-fi, I'd point you towards stellar engines. The thought process here is that the Earth already provides radiation shielding, and the Sun already burns fuel to provide massive amounts of energy, so we might as well just make use of what we got! Add mirrors to concentrate the Sun's light in one direction, and our entire solar system becomes an interstellar spaceship. It might take millions or even billions of years, but the Sun has enough fuel to accelerate the whole system to about .27c.

https://en.wikipedia.org/wiki/Stellar_engine