Moontanman

Where I live you can conceal carry a pistol to deal with a personal attack. Most aggressive assholes will hesitate to hassle someone they think can shoot them. Aggression is easy when you think the person you are hassling is helpless. Most people around here keep their pistols in their cars most of the time but I'm not adverse to taking it with me where ever I go, I wouldn't want to shoot anyone, lots of paper work involved, but if faced with the prospect of taking an ass whipping or pulling my gun i would pull my gun. Anyone who doesn't back down from a pistol probably needs to be shot. Of course I live where the legal defense of "he needed killin" is a viable defense in court. ;)On the bright side the number of people who actually get shot by citizens with pistol permits is almost nonexistent.

Agreed, a nuclear rocket with a solid core can easily give an ISP of 900 twice that of the best chemical rockets. No amount of tweaking the design of rocket nozzles will ever give us an ISP even close to that.

A gaseous core nuclear reactor can give us an ISP of 5000 more than 10 times as much as the best chemical rockets. Yes I think nuclear will be the way to go once we get the superstitious fear of nuclear out of our social mind set. see this link

http://www.nuclearspace.com/Liberty_ship_menupg.aspx

While I think there is reason to think they were exclusively freshwater I will wait until I read the book you cited before I argue any further. I have burnt the Internet up looking for info and all I could get was a few tantalizing clues and generalizations. I see no reason to continue with out more information. I'll continue to search and read the book.

Archegosaurus

Again Archegosaurus was a freshwater form not marine.

Dinosaurs weren't tied to water for reproduction, though.

 

Neither are reptiles, or mammals but they evolved forms that were marine. What's your point?

Given that there is copious evidence of marine sacropterygians, I see no reason to assume, a priori, that a very closely related group was restricted to fresh water.

Why would the distribution of fish have anything to do with the distribution of amphibians? I have already said that lobe finned fishes were marine and freshwater but amphibians evolved from the freshwater versions.

http://en.wikipedia.org/wiki/Sarcopterygii

Archegosaurus were freshwater forms, they were associated with freshwater deposits not marine.

BTW I will be the first to admit this is an extremely difficult thing to nail down, I'm betting that very little real information exists on the overall ecology of these animals.

Theoretically, it's possible, but there's no reason to assume permeable skins evolved until modern amphibians (which arose in the Triassic), especially given the marine tetrapod species I listed above, and that even freshwater poses osmotic challenges (just in the opposite direction).

Ok, I know enough about fishes to know about osmotic pressure and even freshwater fish benefit from the addition of a small amount of salt, it lessens the stress of capture. But I still disagree with the contention that tetra pods had to be able to swim and or live in the oceans for them to have populated the Earth. The fossil record doesn't show any oceanic amphibians even thought they've been around longer than other tetra pods. Even dinosaurs didn't return to the ocean but they were world wide in distribution so the idea that Pangaean deserts would've required amphibians to colonize the oceans isn't worth it's salt

While I'm not a rocket scientist is do know one:D I do agree that improvements will always be possible but at some point you come up against the idea of diminishing returns. The real problem with rocket engines isn't the design of the engine it's the fuel. The theoretical limit of current rocket fuels is an ISP of about 450

Specific Impulse is often abbreviated as ISP. Isp is a little more complicated, but it is very important. ISP is sort of like the fuel efficiency of a rocket. It is easiest to explain with an example. The two giant rockets we use to launch the Space Shuttle have an ISP of about 250 at takeoff. What this means is that for every pound of fuel they fire out the back in a second, 250 pounds of thrust is generated. Simple! Another way of looking at it is if you have an ISP of 250, you can make one pound of thrust for 250 seconds. High ISP is very important for efficient rockets. ISP is very like fuel economy for a car. If one car has a very old motor that makes 100 horsepower but gets 5 miles per gallon, and a second car has a new motor that makes the same 100 horsepower but gets 50 miles per gallon, which one would you rather have?

http://www.nuclearspace.com/Liberty_ship_pg6.aspx

The best chemical fuels in use today are liquid hydrogen and liquid oxygen, the stuff burned by the three Main Engines on the Space Shuttle (SSME's). The SSME's produce a maximum of about 450 Isp.

http://www.nuclearspace.com/Liberty_ship_pg7.aspx

Ok, now the main engines of the space shuttle have an ISP of about 450. That is pretty close to the limit of chemical fuels, you can get a tiny bit better by using something like liquid Florine but besides being a very dangerous chemical the exhaust is not very nice either. Liquid Hydrogen and oxygen only produce water vapor.

So not matter how good you make a chemical rocket engine it has a limit as to how much energy you can get out of the fuel, IE an ISP of about 450.

Clack's book is the source. I doubt land migration would be possible - most early tetrapods weren't good enough walkers for long-distance migration, especially over the inner desert of Pangaea.

While I will have to read the book to understand your argument completely I wonder why you think migration due to long distance would be a problem. A species of salamander could migrate long distances over millions of years taking advantage of changing climate patterns. We would think the idea of a fish migrating across the Sahara Desert would be impossible but just a few thousands years ago what we know as a desert was a lush area with rivers and lakes and lots of rain. A fish could well have migrated over that area then. I am quite sure that Pangaea had changing climate patterns as well and over a geologic time span an animal could well have migrated all over it while speciating along the way. No need to swim and oceans or migrate across burning sands.

Where do you get that Archegosaurus lived in the ocean? It is described as living in freshwater ponds that were subject to drying up and Archegosaurus was able to wiggle over land to a new pond. No mention of marine existence.

Do you think it might have been possible for tetrapods to have migrated over Pangaea before it broke apart?

If origin determined the entire future of the lineage, why are there marine organisms of all other tetrapod lineages? That a lineage originated in a given environment does not constrain it forever to that environment. See Whales.

 

I suggest Clack's book, which has a good discussion on this. She specifically points out that the global distribution of tetrapod fossils means they must have been able move through marine environments (as the alternative, numerous independent origins, is even less likely).

This is true my logic did faultier there but I did say I had no idea if amphibians had ever adapted to the sea or not. fossils seem to indicate they didn't. The plain fact is not many land animals have ever adapted back to the oceans. Yes I know whales, Plesiosaurs, turtles, seals but not many compared to the number of land animals. Paradoxically dinosaurs never adapted to marine life. If any amphibians did go back to sea they are all extinct now and left little or no fossil evidence. Evidently it's hard jump and thin skinned amphibians seem to be somewhat less than preadapted to marine conditions. As far as the global distribution drifting continents would seem to explain that pretty neatly.

Ok guys, there are no marine amphibians because they developed from bony fishes, Bony fishes evolved in fresh water, not marine. The skeleton of freshwater fishes evolved from fishes with no bones much like sharks, they migrated to fresh water to lay their eggs. the calcium was concentrated in their skeletons so they wouldn't loose it when they entered freshwater. Calcium is important to all animals far beyond the need for bones. The cartilage bony fish that concentrated calcium were preadapted to life in freshwater. True bony fishes developed in freshwater and later returned to the sea. Amphibians evolved from a group of bony fishes called lobe finned fishes that may have only survived in freshwater due to the highly succesful Placoderms.

http://en.wikipedia.org/wiki/Placoderms

I honestly cannot say if amphibians ever returned to the sea or not but they evolved in freshwater from freshwater fishes. the coelacanth probably evolved from a lobe finned fish who's lineage never left the ocean.

http://en.wikipedia.org/wiki/Coelacanth

The modern bony fishes, class Osteichthyes, appeared in the late Silurian or early Devonian, about 395 million years ago. The early forms were freshwater fishes, for no fossil remains of modern bony fishes have been found in marine deposits older than Triassic time, about 230 million years ago. The Osteichthyes may have arisen from the acanthodians. A subclass of the Osteichthyes, the ray-finned fishes (subclass Actinopterygii), became and have remained the dominant group of fishes throughout the world. It was not the ray-finned fishes, however, that led to the evolution of the land vertebrates.

http://www.lookd.com/fish/evolution.html

Tetrapods evolved from freshwater lobe finned fishes, the fishes you see in the rivers and oceans today are not the direct ancestors of us, Only the coelacanth and some lung fishes remain from those lobe finned fishes. the coelacanth is not a direct ancestor either but it is closely related.

http://www.devoniantimes.org/who/pages/lobe-fins.html

http://en.wikipedia.org/wiki/Lobe-finned_fish

Ok, I'm not trying to be obtuse here, i am really trying to understand. I understand that from the stand point of both twins their own clocks are running at the normal rate. Both see the other as having a distorted time frame. Both see the other as foreshortened, more massive and time slowed. Why is reality the of the twin who is moving the only reality that turns out to be real? it's all relative, neither twin can say who is moving until one of them stops. Why is one reality real the other not?

"Don't Fear the Reaper" is probably their most famous song, lots of good stuff.

Massive Attack is cool, my son turned me on to them. Blue Oyster Cult is good for long slowly changing tracks that keep you drifting.

Well it wouldn't be proper to say on this forum but yes, there is something better than music but it can be enjoyed while listening to music, of any kind even Blues or Jazz...... But I enjoy as I said Heart the best.

If I had to guess I would say chlorine did it. Over time chlorine will erode most white or clear plastics.

The Music of Heart always does it for me, something about Ann Wilson's voice sooths the beast in me !

It would seem there is a real difference in the way chimp muscles and human muscles actually work.

So the figures quoted by primate experts are a little exaggerated. But it is a fact that chimpanzees and other apes are stronger than humans. How did we get to be the weaklings of the primate order? Our overall body architecture makes a difference: Even though chimpanzees weigh less than humans, more of their mass is concentrated in their powerful arms. But a more important factor seems to be the structure of the muscles themselves. A chimpanzee's skeletal muscle has longer fibers than the human equivalent and can generate twice the work output over a wider range of motion. In the past few years, geneticists have identified the loci for some of these anatomical differences. One gene, for example, called MYH16, contributes to the development of large jaw muscles in other apes. In humans, MYH16 has been deactivated. (Puny jaws have marked our lineage for as least 2 million years.) Many people have also lost another muscle-related gene called ACTN3. People with two working versions of this gene are overrepresented among elite sprinters while those with the nonworking version are overrepresented among endurance runners. Chimpanzees and all other nonhuman primates have only the working version; in other words, they're on the powerful, "sprinter" end of the spectrum.

http://www.slate.com/id/2212232/

From the point of view of the space ship twin wouldn't it be the earth twin who's time was slowed down? Since from his point of view it would be the rest of the universe that was time dilated?

I have a struggle to understand how relativistic mass is real if the observer that is traveling close to the speed of light sees the rest of the universe as massive and time dilated but the at rest observer sees only the speeding object as time dilated and massive. How can both be correct? also when the fast observer is slowed down only his time dilation proves to be real, the rest of the universe has aged at the same rate it always has. Only the time dilation of the fast observer is real when he slows down.

ok. i thought up another one. i know, been a while. my bad.

alright. so, if say, we filled mars with alot of windmills, and then brodcast that harvested electricity through radio waves back to earth, well, after a while, wed be getting all this free energy, but what would be happening to mars? the wind wouldnt just stop would it? but, judging on this post, theres only the energy that there is, no more no less.{if that makes sense}. so what would happen on mars after we harvested all that energy off of it just through wind. and solar, but thats external source anywhay, so no need to worry about that one.

I think it needs to be said that the wind on Mars contains very little energy when compared to wind on the earth. a 100mph wind on Mars it's a gentle breeze on the earth in terms of energy content.

Add that to the losses incurred while beaming this energy to the Earth and you get a strong radio signal but almost no net energy increase.

Every time a thunderstorm blows through I hear his thunder, how could you doubt such a display

Um, why couldn't a Great Dane bitch have puppies by a chihuahua sire?

could you have something like a fan, wich the propellers were connected to small generators, and theres also mini windmills on the blow-side wich take in energy from there too. would it make more than it used?

No, absolutely not.

it uses 2 energy supplies to make it, the mechanical energy of the fan blades moving, and the wind energy from the moving air. i think it might help if it was all in an airtight "shell" too. and if it could work then it could also be used in bigger curcamstances.

Again no it would not work, you cannot get more energy out of system than you put in, you cannot even break even. Friction will always keep you from even coming close.

First I have to say I think it's possible that aliens are already here, not on the Earth but inside our solar system. If you give any credence to UFO reports (I'm not saying I do but lets assume that reports are real, at least some of them) then you have three basic choices.

#1. They have a practical FTL drive for their space craft.

In which case all bets are off, we are not playing with a full deck when it come to physics and they can be up to almost anything.

#2. They are here but it's a one hit wonder, an exploration craft is here, it was a slow trip and they intended to either colonize or explore.

#3. They have been here for millennia, they are part of a colonization effort that is based in space instead of planets. Like artificial colonies and they are only interested in the the resources of the asteroids and comets. They have been spreading from stat to star for tens of thousands or hundreds of thousands of years at least. There interest in us is only along the lines of our impact on their operations here.

A more practical use for such technology would be creating plants than have real meat as fruit. Possibly a pod the size of a coconut that contains beef, shrimp, or fish or what ever meat you want.