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Water found on a potentially life-friendly alien planet

nationalgeographic.com

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Re: Water found on a potentially life-friendly alien planet

#231

Post by ryacko »

SJSque wrote: post #17
transreal wrote: post #2

With a planet this large, visiting it would be a one way trip due to the "The Tyranny of the Rocket Equation" [0]. I'm looking forward to the day we start finding exo-planets that are closer to Earth in size and which could potentially have space-faring races (and which we could leave if we were ever to visit them). [0] - https://www.nasa.gov/mission_pages/station/expeditions/exped...

There's also the Wait Calculation to consider: https://en.wikipedia.org/wiki/Interstellar_travel#Wait_calcu...

The wait calculation implies that the returns from economic growth will eventually be converted into rocket fuel. A fun equation, but economics doesn’t translate well on time scales where depreciation of capital is 100% and becomes another expense.

Re: Water found on a potentially life-friendly alien planet

#232

Post by outworlder »

usrusr wrote: post #68
kadoban wrote: post #42

Earlier quoted context omitted.

How poor of a shortcut is it? I'm not really clear on what the math would look like. Would it just be better by approximately the ratio of gravity's strength at the surface vs the height of the balloon?

Better than the miniscule gain in potential energy (height x mass x gravity) because you also save a lot of aerodynamic drag not punching through the lower atmosphere at high speed and some "hovering losses" (rise time x mass x gravity, I'm sure there is a better term for that). But still not worthwhile due to the difficulty of floating a full size rocket. If you had a very very high mountain or tower, moving that fu…

> "hovering losses"

Gravity drag

Re: Water found on a potentially life-friendly alien planet

#234

Post by nkoren »

gdubs wrote: post #56
dkural wrote: post #52

Earlier quoted context omitted.

Light does not experience time at light speed - it is stuck in a static moment. So from our stationary perspective, light takes 111 years to come from a 111 light year distance, but from light's perspective it takes an instant.

Every time I think I’m closer to understanding matters of time and space...

Here's a quick analogy to help (loosely adapted from Brian Greene):

You're on a grass field, sitting on one of those riding lawnmower thingies, with a broken throttle. It's moving at a fixed speed of 1mph. You can't ever change its velocity. But you can steer it. If you are going precisely east-west, then it means you're not going north-south. The more you go north-south, the less you'll be going east-west. If you're going precisely north-south, it means you're not going east-west at all. One direction is traded against the other.

Pretty straightforward, right?

So here's the analogy: that grass field is a "dimension" in the same way that "spacetime" is a "dimension". The two "directions" of spacetime aren't "east-west" and "north-south", but "space" and "time". These are inherently traded against each other. The more you're moving through one, the less you're moving through the other.

So what about that constant-velocity rideable lawnmower? That's "c" -- the speed of light. You're always traveling at this velocity. If you are sitting still in space, then you are nonetheless moving through time. Your rate of movement through time is "c". But as soon as you start moving through space, it means you are moving less through time. This is exactly the same tradeoff as moving north-south vs. east-west. If you devote 100% of your "c" to moving in the direction of the "space" axis, then it means you're not moving on the "time" axis at all.

(This is basically all it means for something to be a "dimension": different axes that are traded against one another.)

This analogy can be used to understand quite precisely how movement relates to time dilation. (It also helped me understand e=mc^2. Why is "c" there? What does the speed of light have to do with the embodied energy of matter at rest? Answer: nothing is ever at rest; all static matter is moving through through time at the velocity of "c", and obviously that movement must have kinetic energy.) But it's not a completely perfect analogy. Weirder relativistic effects like length contraction and frame dragging need much weirder analogies.

Re: Water found on a potentially life-friendly alien planet

#235

Post by [deleted] »

solipsism wrote: post #199
saagarjha wrote: post #193

Earlier quoted context omitted.

The point is finding planets aside from our own .

Sometimes N=2 is extremely different from N=1. Specifically when we have N=1 and we suspect that it might be unique, or extremely rare to the point that you wouldn't expect to find instances. Sometimes N=2 is not that different from N=1 though. Specifically when you don't think the situation is necessarily that rare, you just don't have a big population to choose from. That's the situation here. Astronomers expect to…

[deleted]

Re: Water found on a potentially life-friendly alien planet

#236

Post by Stratoscope »

mr_toad wrote: post #203
caf wrote: post #192

Earlier quoted context omitted.

I am amused by the idea of a "small giant".

Neptune is ‘only’ 57 times the volume of Earth, whereas Jupiter is 1321 times the volume of Earth. The size range of ice/gas giants is bigger than the gap between Earth and the smallest ice giants.

Does it make sense to compare both Neptune and Jupiter to the Earth? I would think the relative numbers for each pair are a more useful comparison.

If Neptune is 57 times the volume of Earth and Jupiter is 1321 times the volume of Earth, then Jupiter is 23 times the volume of Neptune.

So the relative difference between Neptune and Jupiter is less than half the relative difference between Earth and Neptune.

As another illustration, let's take a different trio of objects: a golf ball, the Moon, and the Earth.

Using very round numbers, it is safe to say that the volume of the Moon is about one zillion golf balls.

The Earth is about 50 times the volume of the Moon, so the Earth is 50 zillion golf balls.

Clearly, the difference between 50 zillion and 1 zillion is much greater than the difference between 1 zillion and just 1 golf ball, by a factor of nearly 50.

Or is it? If you ask anyone on the street, they won't have to calculate anything, they will tell you that the Earth and Moon are much more similar in size than the Moon and a golf ball. That's because they are using relative sizes, not absolute.

Re: Water found on a potentially life-friendly alien planet

#238

Post by vermilingua »

narrator wrote: post #230
tunesmith wrote: post #204

I got into the Wait Calculation[1] a few weeks back and made a Jupyter notebook out of it. At our current max speed (692,000 km/hr, stated max speed of Parker Space Probe), it would take about 173,000 years to get to that planet. We could instead choose to Wait and grow our tech. By picking a constant annual growth rate and then doing some calculus to find the minimum, we can calculate the shortest possible time it w…

Progress in physics was much faster in the early 20th century when it wasn't so fascinated with deep space. Yes, you needed to observe eclipses to verify relativity, but that was a tool, not the end in itself. Cosmology involves distances that are so great that it seems like it's pouring a whole bunch of smart people's efforts down the drain in an ultimately futile waste of brain power that will never amount to anyth…

> when we get faster than light travel

FTL requires numerous things to be true about our universe, that all signs say are not.

Re: Water found on a potentially life-friendly alien planet

#239

Post by Swizec »

jackvalentine wrote: post #225
Swizec wrote: post #218

Earlier quoted context omitted.

Where can you invest that would still recognize those funds as yours after 222 years?

You'd have to form some kind of trust, the "Swizec is in space for 200 years trust" to handle your investments for you with a constitution that lays out how long it is expected for you to be gone. You might come back to discover that after several generations without oversight your trust has invested in bombing children and enriching the fund managers. I dunno.

You still get in trouble I think. Have any political regimes been stable enough in the past 222 yaers for the trust to survive?

All of Europe has gone through multiple revolutions, USA was only 30 years old back then so you wouldn’t have considered it ... that leaves what, the UK? Any parts of Asia that survived since 1797?

Re: Water found on a potentially life-friendly alien planet

#240

Post by glup »

vermilingua wrote: post #238
narrator wrote: post #230

Earlier quoted context omitted.

Progress in physics was much faster in the early 20th century when it wasn't so fascinated with deep space. Yes, you needed to observe eclipses to verify relativity, but that was a tool, not the end in itself. Cosmology involves distances that are so great that it seems like it's pouring a whole bunch of smart people's efforts down the drain in an ultimately futile waste of brain power that will never amount to anyth…

> when we get faster than light travel FTL requires numerous things to be true about our universe, that all signs say are not.

...crushing all my dreams of being a starship captain, thanks.
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