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4 hours ago, Eric S said:

 I think that's BS since Newton himself said that all parts of the 'Earth are attracted to each other.

So do i :-) If i get it right Newton actually did away with the elder concept of entities (identities ?) and put masses and quantities instead, thus principally enabling calculation of forces like the one that pull a planet into a sphere.

But that is just an interpretation,  i have not read his work myself.

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3 hours ago, Eric S said:

Right, the particles affect the other particles, he's saying that the entire mass of the planet has no effect on any part of the planet according to Newtonian gravitation as described in Principia.  Another reason that I think this is BS is that one of the masses Newton used in his experiment was grain (or was it rice?), and at that point, any "identity" would have to be strictly conceptual.  I can see what's wrong with that logic and I really doubt Newton wouldn't have seen it, but while I've read Principia, I haven't actually studied it in depth, so it's possible I missed something.

 

Depend on how you look at it, for the moon it don't matter if earth was an singularity of the same mass. 
Gravity in KSP is in fact from an singularity in the center of an shell who is the planet surface. 
(note that gravity in real world is not uniform, Moon has in fact significant differences because asteroid masses who makes low orbits unstable)

Gravity in senter of the earth is zero, as you move toward the surface it grows. 
Say you grind up earth and evened out the materials in an one million km diameter sphere the gains in center would not feel any gravitational pull the particles outward would and the sphere would collapse into an planet again. 
 

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16 hours ago, Eric S said:

Right, the particles affect the other particles, he's saying that the entire mass of the planet has no effect on any part of the planet according to Newtonian gravitation as described in Principia.

My Latin's rusty, so this is based more on the general knowledge available at the time and the state of early Calculus than on actual reading of the Principa text. But Newton had all the machinery to realize that a spherically symmetrical body has the exact same gravitational pull as a point mass. Once you have a hypothesis that force of gravity drops as inverse square of the distance for any component masses, deriving the fact that planets will have force between them proportional to total mass and inverse square distance between their centers is relatively straight forward. Which then confirms the inverse square hypothesis via Kepler's Laws. Showing that Elliptical orbits satisfy both is a bit more work, and I believe initial proof is due to Hooke.

Anyways, where I was going with this is that it's very likely that Newton would have pointed out that spherical bodies behave as point masses. That's not the same as saying that objects have no self-interaction via gravity. Just that we can ignore it while talking about motion of planets and other celestial bodies. But it could possibly be misread to imply it.

As for actually showing that a shape of a planet should be roughly a sphere, the simplest argument is via potential energy. A more rigorous proof involves a bit of Calculus of Variation. So I don't know if a good way to prove it was available to Newton, but it's a pretty intuitive notion that things trying to clump together as close as possible might make a sphere.

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20 hours ago, Eric S said:

I think someone is pulling my leg in a discussion on physics, and just wanted to get another opinion, if anyone cares to check my understanding.

I've read Newton's Principia, and while I don't doubt that we've refined things since then, even disregarding relativity and QM. However, someone's insisting that according to Principia, a forming planet couldn't pull itself into a sphere because Newton's concepts at that time didn't allow a mass to affect itself.  He claimed something about Newtonian mass having the concept of identity.  I think that's BS since Newton himself said that all parts of the 'Earth are attracted to each other.

Any two particles floating in space will attract each other, so ignoring all forces, any collection of particles will eventually form into something that's roughly spherical.

Maybe what your friend is talking about has something to do with the shell theorem?

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Several with two different keys for dit and dah, when searching "convert morse code key press". Example https://github.com/willwade/MorseWriter

But it would be a nice little exercise to read the timing of a single key press and release and translate it to dit and dah. Depends on OS of course ....

Edited by Green Baron
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Reading timing is harder, because it varies with your input rate, especially for inexperienced operator. But I'm almost certain I've seen software that does it.

There's also minor complication in variation of input styles, like fast double dit for dah. But this can be a toggle flag. Not something that needs to auto-detect.

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True. Programming wise it is trivial (using xcb which is the only basic event handling api i know).

One would have to parametrize the durations and the beginner has to type in a disciplined manner (not KSP style, eh ?).

Or let him type something and deduct the timing from medians of his strokes. Including variations for time of day, relative humidity, sleepiness of eyes and spectroscopic analysis of the gases in the user's exhaled air.

A field for playing, for sure :-)

 

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9 hours ago, Green Baron said:

True. Programming wise it is trivial (using xcb which is the only basic event handling api i know).

One would have to parametrize the durations and the beginner has to type in a disciplined manner (not KSP style, eh ?).

Or let him type something and deduct the timing from medians of his strokes. Including variations for time of day, relative humidity, sleepiness of eyes and spectroscopic analysis of the gases in the user's exhaled air.

A field for playing, for sure :-)

 

Yes and the same would be true for an human receiver. I assume lots of the telegraphists in edge towns in the west was not very experts in Morse either, and had their wife stand in as he was sick. 
its also why computers use the clock signal and on or off even if this again get a bit blurred 

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7 hours ago, magnemoe said:

its also why computers use the clock signal and on or off even if this again get a bit blurred 

If the clock signal is available, yes. But we also have types of digital media where it's not, like compact disc. There you have things like requiring that no code point consisting of only zeroes is used, meaning you will have a signal at least every so often letting you re-calibrate and adjust for slight difference between physical speed of the disk and expected clock rate. It also helps that ones are encoded as the change in the depth of the disk, rather than specific value. But this has more to do with the fact that interferometer is used to read the distance, and that's really good at telling that distance changed, but not necessarily whether it got longer or shorter. Still, it works out to make tracking of the medium's speed a bit easier, so it's an added benefit.

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On 10/16/2018 at 12:57 PM, Terwin said:

That law works at just about any scale.

A closed life-support system is impossible without at least energy input for example, and for any complex system entropy will increase within that system(parts wearing out and breaking down for example).

Why then do senescence rates in eukaryotes vary between mere weeks and literal centuries? The whole point of biology is to temporarily defy entropy. It may well be true that completely forgoing it is impossible, but no one has suggested that have they?

Point is: sound biology doesn't defy physics or chemistry, but physics and chemistry cannot fully explain biology. The fact a bristlecone pine ages so much more slowly than a frog or a house cat can be reduced down to the level of chemistry and physics and what we would find at that level is: biological system "working around" the rules of the universe which are coarsely represented by human conceptions like "laws."

It seems to me that very few of our "laws" are truly law like given the necessity of x-variables like dark matter and dark energy.

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On 10/16/2018 at 5:47 AM, Green Baron said:

Found a somewhat up-to-date study or better collection of ideas on interstellar travel.

https://www.researchgate.net/publication/323810028_Concepts_for_Deep_Space_Travel_From_Warp_Drives_and_Hibernation_to_World_Ships_and_Cryogenics

Tl:dr: Colonizing other bodies outside our solar system is many hundred years away. Practicing in our system would be the first step.

 

Interstellar travel stays a fiction for now ...

That is a good find, I appreciate it.

It makes the point I was attempting to argue, i.e., that hibernation, stasis or something along those lines is a plausible means for humans to undertake interstellar travel. Not yet a proven technology, and perhaps never actually achievable, but plausible, unlike say FTL which is implausible. That in my opinion is the key distinction between hard and soft science fiction; your distinction apparently being 'if it doesn't already exist then it is soft science fiction, if it already exists, but only in very limited form then it counts as hard science fiction'.

Quote

Nevertheless, despite the challenges, the potential for human stasis to support deep space travel is a very active area of research which benefits from technology which is being developed on Earth for treatment of acute injury.

 

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Thanks :-)

Yeah, the article is on the fantastic side in some parts.

Stasis for humans does not exist. All info i ever found or asked, as well as the articles we browsed upthread, are about temporary cooling of body parts by a few degrees and for hours, under intensive observation and attention by medics, to prevent deterioration for a transport into hospital for example.

For now, lowering body core temperature below 30 degrees celsius is life threatening.

Maybe in the future, who knows :-)

I have absolutely no problem using hibernation in a scifi works. I only objected that it is no hard scifi because nobody knows how to do it yet (how to prevent a body from dying) and it is not as clear that it will work as is for example fusion energy, where we know that it works, have the first small experimental results, "just" look for an industrial realization.

Edit: btw., in another thread, we came to the conclusion that accelerating a mass of 1 ton to 0.2c requires many magnitudes more than the mass of the whole observable universe as reaction mass, even with electric superpower ion drives. You We actually need a drive that accelerates reaction mass to relativistic speeds and even then millions or billions of tons for every 1 ton.

So, anyway, you we probably need wormholes or warp drives or some magic to tap vacuum energy to reach other stars with humans on board.

Valid until the contrary has been proven :-)

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1 hour ago, Diche Bach said:

Why then do senescence rates in eukaryotes vary between mere weeks and literal centuries? The whole point of biology is to temporarily defy entropy. It may well be true that completely forgoing it is impossible, but no one has suggested that have they?

Point is: sound biology doesn't defy physics or chemistry, but physics and chemistry cannot fully explain biology. The fact a bristlecone pine ages so much more slowly than a frog or a house cat can be reduced down to the level of chemistry and physics and what we would find at that level is: biological system "working around" the rules of the universe which are coarsely represented by human conceptions like "laws."

It seems to me that very few of our "laws" are truly law like given the necessity of x-variables like dark matter and dark energy.

Entropy is just a measure of chaos, nothing more.

It connects abstract world of mathematics
EntropyOfSystem = ln(NumberOfSystemStates)

with material world of physics
d(EntropyOfSystem) = d(EnergyOfSystem) / T

Nothing forbids entropy to decrease. 

Information is the same but with opposite sign of delta.
When the number of your system states gets less (when you resolve some indeterminance) delta information > 0, delta entropy < 0.

The 2nd law of thermodynamics is like have become a kind of religion.

Edited by kerbiloid
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3 hours ago, Green Baron said:

So, anyway, you we probably need wormholes or warp drives or some magic to tap vacuum energy to reach other stars with humans on board.

Is there a limit on how long a generation ship could last? Let’s see, it would take a thousand years at 0.01c to cross ten light years... 

We really need to figure out a  reactionless drive. If only the emdrive worked...

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On 10/28/2018 at 6:46 PM, magnemoe said:

Yes and the same would be true for an human receiver. I assume lots of the telegraphists in edge towns in the west was not very experts in Morse either, and had their wife stand in as he was sick. 

I've read that skilled telegraph operators could tell who they were talking to just by the style of the code they were receiving.   This was their job, and they would frequently encounter the same other operators.     They would probably know when an operator called in sick from a small station, as it would just 'sound' weird.

1 hour ago, StrandedonEarth said:

Is there a limit on how long a generation ship could last?

I'd say no, given unlimited resources, space or the ability to regulate that space.   With recycling, you can almost have unlimited resources, but those recyclers wear out, and you'll need some way to fix them.   As for space/room, you either A) build a huge ship with lots of empty space and the infrastructure to support an expanding population, but you will eventually run into B) where you need some Draconian population control methods, either through limiting birthrate and or eliminating 'excess' population. 

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8 hours ago, Gargamel said:

I'd say no, given unlimited resources, space or the ability to regulate that space.   With recycling, you can almost have unlimited resources, but those recyclers wear out, and you'll need some way to fix them.   As for space/room, you either A) build a huge ship with lots of empty space and the infrastructure to support an expanding population, but you will eventually run into B) where you need some Draconian population control methods, either through limiting birthrate and or eliminating 'excess' population. 

You have two problems, one is loss, air will leak, some materials are uses very diluted and will be hard to reclaim. You also has erosion of frontal armor. 

More serious problem as you say is repair, you need to be able to not only repair but also rebuild any part of the ship. 
Its an problem much like an self dependent Mars colony however you have mass restrictions and limited supply of resources. 

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So, the velocity limit for the interstellar craft is probably ~0.05..0.1 c. (By both ship mass ratio and interstellar drag heating).

The crew life duration limit is probably ~200 years (cells degradation), no matter is the habitat cool or hot.

Workable systems lifespan is probably somewhat similar.
(There are many critical systems in such ship, so redundancy and repair have humble abilities.
Unlikely you can make the ship 3-in-1 reduntant, and the longer it flies, the greater is the probability of simultaneous malfunction or unexpected behavior).

This gives us ~10..20 ly radius of a biological species space expansion.

Like there is a 10 km/s threshold keeping a species on the planet (i.e. inside a 10000 km sphere), or just several meters of muscular abilties.

This looks very wise and good, as it keeps every sapient plague inside its invisible glass.


I guess, unless somebody invents some way of fast travel, to reach the stars beyond 20 ly a biological species should first create a self-upgrade which most probably stops it being biological.
The biology should first become an engineering discipline rather than empirical one.

(I.e. the criterion of a long-range interstellar epoch is when instead "Save the whales!" there will be "Why you can't just make a whale at your wish if you so much need it?")
Of course at this stage the natural human biobodies get obsolete and arbitrary).

Edited by kerbiloid
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On 10/29/2018 at 12:30 PM, Diche Bach said:

Why then do senescence rates in eukaryotes vary between mere weeks and literal centuries? The whole point of biology is to temporarily defy entropy. It may well be true that completely forgoing it is impossible, but no one has suggested that have they?

Longevity generally has little to do with entropy until you get to galactic time-scales.

So long as an organism is consuming energy, they are generally contributing to entropy(often as waste heat), the ability for  cell to repair damage with some of that energy does not counter the fact that the processes starting with capture of the energy and through every use of it, is less than 100% of theoretical efficiency, and thus increasing entropy.

You could have an amoeba that was formed mere seconds after the big bang and expecting to live until the heat-death of the universe without violating the second law in any way.

On 10/29/2018 at 12:30 PM, Diche Bach said:

Point is: sound biology doesn't defy physics or chemistry, but physics and chemistry cannot fully explain biology. The fact a bristlecone pine ages so much more slowly than a frog or a house cat can be reduced down to the level of chemistry and physics and what we would find at that level is: biological system "working around" the rules of the universe which are coarsely represented by human conceptions like "laws."

It seems to me that very few of our "laws" are truly law like given the necessity of x-variables like dark matter and dark energy.

Yes, physics can fully explain chemistry, and between them, physics and chemistry can fully explain biology(you might be able to do it all with chemistry, but some things like muscles and bones working together for mechanical advantage are easier to explain through straight physics)

What are referred to as 'Physical Laws' are theories that have stood the test of time and been validated by every test that anyone has come up with thus far.  While some are considered to be incomplete(here is looking at you gravity), that does not mean that we have any known way of violating those 'laws', not with  chemistry, biology, or anything else.  The closest you will get to violating physical laws is with unproven theories, generally things that are not taken seriously by the scientific community.

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These are simply the gaps in our knowledge and understanding that may seem like physics couldn't fully explain nature. I would even say that, in the case of biology, our understanding of how organisms function and play together and evolve is pretty good, has made quite a few leaps forward in the past decades.

Edited by Green Baron
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Why (Most) tracked vehicles can't operate when it lost track links (As in, using only wheels (that moves the track in the first place) without the caterpillar track)?

Edited by ARS
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