So if you plan to take your laptop it is better to upload the disk image and buy a new one in the states? I'm assuming the TSA can force a foreigner to unlock and then copy the disk.
I've entered the US through SeaTac, MSP, ATL, and SFO. In each of those, I never encountered TSA checkpoints until a connecting flight. If it is the final destination of your flight, you do not interact with TSA at all (unless you scream bomb in the airport or something).
Agreed. I've entered via SFO, SJC, ATL, JFK, LGA, MIA, HOU, and DFW and it's only CBP at the customs & immigration check... then onward to baggage rescan & TSA security checkpoint.
And the last paragraph is the main problem. The ship would get torn apart from lone atoms and to actually stop yourself you need an exponential amount of fuel, because you need to accelerate ( much more than )half of it just to stop yourself.
Even if you protect yourself from relativistic atoms, they still create a drag. And that happens before you reach 0.99c.
Yeah, the energy issue is really, really tough. Stars are very, very, very freakingly far away.
I'm in California. If the whole Earth was this 2mm breadcrumb, then the Sun would be a soccer ball 25m away (across the street). Speed of light would be the speed of a running ant. Uranus would be a peanut 1/2km away.
And the nearest star would be another soccer ball somewhere in Greenland.
I look up at the sky often. Those specks of light are so incredibly far away. We just need new physics, otherwise we'll never get there.
I'm an amateur astronomer and telescope maker, on a quest to see what's the biggest aperture that an amateur could build working alone. I can't go to the stars, but I can bring them a few hundred to a few thousand times closer to the eye.
I have to say I love the "speed of a running ant" analogy. It really emphasises the size of the universe.
But can an ant run 25m in 8 minutes? I honestly can't imagine how fast an ant runs. That would be a foot in 4.8 secs - that's a fast ant actually. But I guess close.
50mm/sec - yeah, it would have to be one of those bigger ants I saw sometimes outside in the summer, hiding in crevices in the sidewalk, while I was growing up in Eastern Europe.
http://www.asu.edu/clas/sirgtools/ecology-1991.pdf says that Pogonomyrmex rugosus travels at 0.1914 * T - 1.983 meters per minute, for ground temperatures T (in C) between 20 and 40. This is roughly 3.8 m/minute or 60 mm/sec.
The equation for Messor pergandei is 0.0878 * T - 0.1724 or roughly 40 mm/sec.
Just to point out a design assumption here, saying that an exponential amount of fuel is required is making 'the rocket assumption': that both the mass and energy required for momentum change are carried with the vehicle, and are expended upon reaction mass.
For travel between star systems, these assumptions do not need to be true. For deceleration, it makes more sense to transfer the original kinetic energy out of the vehicle's movement than to expend even more energy on accelerating reaction mass yet even faster in the original direction of travel. Remember that you have a whole star system of reaction mass at your destination. There may be engineering challenges, but there is no physics reason why you couldn't expend your original energy in "pushing off the sun", and then recover it by "pushing against the new sun" when you arrive. Depending upon efficiency, this could then leave you with the energy for another flight (perhaps home).
edit: Nevermind - you're totally right, and I'm totally wrong - I didn't think it through, and didn't realize that since relativity helps you less and less as you decelerate, the amount of fuel required does increase hugely if you actually want to stop at your destination.
Unedited original post follows:
> to actually stop yourself you need an exponential amount of fuel, because you need to accelerate half of it just to stop yourself
Hang on, I don't understand this part. First, you're right, I didn't think about deceleration - but that only doubles the trip length at most, since you have to accelerate halfway, then decelerate halfway. And probably not even exactly that if you're carrying your fuel, since deceleration will be a little bit easier - you've burned some gas, so there's less mass to push around.
And you're right, I didn't think about the drag - but that actually works out better for extragalactic visitors! There isn't as much stuff there to stop them when they're taking off, and once they hit a galaxy, it actually helps them decelerate. (Again, my dreamy eyes are ignoring the practical hazards of this "help" which might just turn them into a fast moving gas cloud.)
Argh, thank you, you're right, I edited my post to reflect that.
I wonder if you could accelerate the whole way in a giant ship, and only slow down a tiny capsule at your 'destination' - maybe just a tiny self-replicating robot factory and some data storage. Decelerate that, land it, have it build you a new body, some tools, etc., etc.
Essentially, any civilization that developed outside of galaxies would need to invent one of two technologies.
The first is the technology to support their culture for a very long time without the support of a nearby star. In that case, there is no particular reason for them to visit galaxies at all. They simply pick a direction and go. Galaxies would be of no particular interest to a civilization that doesn't even need one star, nor would they need to travel at particularly high accelerations.
The second is a propulsion technology that does not require reaction mass (or reaction energy, as with laser propulsion). You would have to devise a way to move something without throwing something in the opposite direction. Thanks to the equations involved, trying to get a long distance away with decent speed using only chemical rockets basically means your ship will start the trip as more than 99.9% fuel by mass.
That is what prompts the imagining of alternate propulsion technologies, such as the Orion nuclear rocket, solar/laser sails, Bussard ramjets, slingshot orbits, and magnetic braking loops. Accelerating the fuel that you will later need to decelerate is a huge problem just for inter-system travel; you can't even bother with it for inter-galactic travel.
If they want to travel anywhere beyond their own isolated system, they would either have to figure out how to leave their star behind or to bring it along with them.
One of these problems is much more easily solved than the other. Either way, that civilization would then have no particular use for galaxies as a travel destination.
Couldn't a galaxy be an attractive travel destination anyway, just like a large city can be an attractive travel destination for country folks? Not necessarily as a place to harvest resources, but as a place to go sightseeing and interact with foreigners.
The short answer is no. Space is really, really, really, really big.
Tourism usually requires that you be alive when you finally get there. At that scale, if you chose to visit even the closest galaxy to ours, not only will you be long dead and thoroughly recycled when your vessel arrives, but the passengers that disembark to snap a group photo might not even be considered Homo sapiens any more.
That kind of commitment can only come from existential necessity. Any visitors to a galaxy that came from outside of one would undoubtedly have a technology that allows travel without actually traversing the intervening distance.
You're assuming that those lurking planets harbor forms of life that even remotely resemble us.
Imagine an alien lifeform with an average lifespan of several million years, perhaps the size of a mouse (not much mass) and with extremely slow metabolism (not much supplies needed for travel). For them, traveling to a nearby galaxy at relativistic speeds (only a few years from the traveler's perspective) might be seen as little more than a nice long vacation. Sure, a dozen lifespans might have passed by the time they get home, but maybe they don't care because they don't have children like we do and their civilization doesn't change much. "They released the Galaxy S9 already? That's crazy! Three new models in a billennium!"
You don't even need FTL transportation if you can afford to spend a few eons strapped to a seat.
Why spend eons strapped to a seat, fixated on your destination, when you can play shuffleboard on the cruise ship while you wait? You are just re-describing the first of my two possibilities--the species so well-adapted to space travel that they never actually need to stop anywhere.
And if they don't need to, they probably won't. If you lived in the country, and wanted to visit the city, you might do so frequently if the trip cost you 15 minutes and $10. You might never do it at all if the trip took 50 years and $100billion.
Space travel is more like the latter than the former.
If, on the other hand, travel to anywhere on Earth cost you 1 second and $0.01, you might just visit every city. That's why I say that any non-galactic visitor to a galaxy is more likely to have a kick-ass travel technology. It's a purely time-based argument, and has nothing to do with any property of the species that has it. They would simply spend far more time at their intended destinations than traveling between them.
A full chapter is dedicated to dynamic type checking.
If that isn't acceptable for your project, don't use it. Successful languages that don't have compile time checks, show that this problem is irrelevant.
The argument is wrongheaded. Implementations of dynamically typed object systems in C do not benefit from using void * all over the place instead of a typed object * pointer.
C itself isn't dynamic and it behooves you to use it as safely as possible if you don't want your dynamically typed framework to fall apart due to easily avoidable bugs.
Whereas you can have dynamic checking which tells you that some object * pointer is a cons cell, vector, string or whatever, if you use void * instead, the type check itself is threatened with undefined behavior:
object *stringp(object *obj)
{
if (is_heap_object(obj) && obj->typecode == TYPE_STR)
return t_obj;
return nil_obj;
}
// ..
{
int x;
if (stringp(&x)) ... // compile-time error!
}
If stringp has the signature
void *stringp(void *obj);
then there is no compile time error; &x happily passes into the function. Moreover, the function has to do an ugly conversion to recover a typed pointer so it has to use it.
void *stringp(void *obj_in)
{
object *obj = obj_in; // cast needed here in C++
if (is_heap_object(obj) && obj->typecode = TYPE_STR)
Dynamic typing is a high level feature that is boostrapped from static typing (whether that typing is checked by a compiler or not!) Static typing means that a given piece of code working on a given piece of data correctly uses that data. For instance if we write assembly code which extracts the bottom three bits of a word, and treats that as a type tag, that is static typing: it's a static fact of the program that that code operates on data with a three bit type tag, and if it is given something else by accident, like a floating-point value without a type tag, it will misbehave.
In short, something has to be rigid at the bottom-most layer. C has enough type muscle to help with that quite a bit without getting in the way too much.
You can just analyze the graphical output of the browser and hence make your hack useless. The underlying problem of this game is just too easy to solve.
@readerrrr: I'm commenting here because HN doesn't let me comment your comment.
> You can always make the game itself harder on top of all the anti-bot tricks.
You are implying two things here. Firstly, that its' always possible to make the game harder and, secondly, that anti-bot tricks can solve this issue.
I'm skeptical about the first part and strongly disagree with the second.
In regard to the first part I'd say that it's hard to make the game harder without making it unenjoyably to play. How'd you integrate a sufficient amount of complexity into this game without ruining the fun? That it's in principle possible shows Go. Interesting problem.
In regard to the second part I say that it's just adding (futile) noise and not tackling the fundamental problem. The player has to see at least the map. He then draws a graph in a program that produces a function that has nearly that graph and gives a string defining that function. The user just copy and pastes it into the game.
You can always make the game itself harder on top of all the anti-bot tricks.
The game has to be only hard and expensive enough to hack so that the effort isn't worth the result.
Of course with unlimited resources you can pretty much solve anything, if you assume those, then everything is easy to solve. But assuming that is simply ignorant.
It's much harder to get the same amount of sugar from actual fruit, as fruit juice is pretty much extracting the sugar and water from the fruit. That is, a glass of orange juice takes more than one orange. The part of the fruit that is thrown out when juicing is also good for you: fiber.
What do you mean by adjust? Is there some withdrawal period from a product like Pepsi? Or adjust to the dissatisfying taste of water compared to sugary drinks?
Sugar is the best and fastest source of energy found in the nature. We are programmed to like it and remember when we ingest it, and that behavior is rewarded by feeling good.
A lack of that feeling will make you feel less good. Experts say it takes up to a month for that imbalance to normalize.
Caffeine withdrawal can give you much more than headaches, and withdrawal can last for at least a week, though generally at higher dosages.
Until I realised what was going on, when I was taking breaks from using 360mg very other day - so equivalent to 5-6 cups of coffee - to boost my weight lifting in periods, I had week long bouts of diarrhoea, intense headaches, shakes setting in in the evening (so severe I had to time my painkillers, or I'd have problems swallowing them because I had difficulty holding my hands steady enough to drink a glass of water), fever, and night sweats.
Caffeine can be a nasty drug to go cold turkey from if your intake has been high. Best bet is to step down gradually (not a long period - over a week or two), coupled with pre-emptively taking paracetamol/acetaminophen in the early evening.
Often, someone who gets a lot of caffeine and starts experiencing symptoms like above may be experiencing withdrawal without being aware.
I'm not saying it's a goldmine of DailyWTF-worth content - but it's still pretty bad. In general, it doesn't really follow any MVC-separation, the naming is arbitraty at best (and dictated by the IDE at worst - Kalkulator1, anyone?), and DRY principles are vastly ignored.
Wow this is sick:
http://www.humblelibertarian.com/2011/06/10-of-tsas-worst-ac...
http://www.washingtonpost.com/blogs/compost/wp/2014/07/07/th...
https://www.youtube.com/watch?v=ba030UmbkCo
http://www.humblelibertarian.com/2011/05/nottheonion-tsa-sea...