# ­xkcd thread **URL:** \ **Category:** Cafe Society\ **Tags:** comic-strips\ **Created:** [May 28, 2020, 12:57am UTC](https://boards.straightdope.com/t/xkcd-thread/854574 "2020-05-28T00:57:03Z")\ **Posts on this page:** 20\ **Page:** 152
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [May 15, 2024, 5:57pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3023 "2024-05-15T17:57:29Z")
> [@dtilque](#): > > [xkcd: Chasing](https://xkcd.com/2931) How is it possible that he neglected to include eclipses? ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [May 15, 2024, 6:15pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3024 "2024-05-15T18:15:56Z")
Yes, I hate this too. I find myself silently screaming at the other drivers to: “TAKE YOUR RIGHT-OF-WAY!!!” On a related note, just this morning, I was in the right lane of the highway as a car started to merge onto the highway and into my lane. I couldn’t move over to the center or left lane because there were two semi-trailer trucks in the other two lanes (which is its own issue, but I digress). So I take my foot off the gas so he can safely merge into my lane. What does this genius do? He sees me, gets nervous, and slows down instead of accelerating! I realize there is no way I can get past him before he runs out of merge lane. The he realizes the same thing and abruptly cuts into my lane right in front of me going about 15-20 mph. Up to that moment I had expected him to accelerate onto the highway, and by the time I realized what he was doing I had to slam on my brakes to keep from rear-ending him. (Yes, I realize I would have been at fault.) And the car behind me nearly rear-ended me. However, the whole issue could have been avoided if he had simply taken merged onto the highway and taken his right-of-way. He was ahead of me, after all. When this all started he had plenty of room to safely merge and I even slowed down a bit so he could do so. ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [May 15, 2024, 6:26pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3025 "2024-05-15T18:26:02Z")
> [@robby](#): > > > [@dtilque](#): > > > > [xkcd: Chasing](https://xkcd.com/2931) ⁢ > > How is it possible that he neglected to include eclipses? ⁢ Not sure where on the chart it would go. I guess you could technically chase it, even though you already know the path. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [May 15, 2024, 6:40pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3026 "2024-05-15T18:40:48Z")
> [@BigT](#): > > > [@robby](#): > > > > > [@dtilque](#): > > > > > > [xkcd: Chasing](https://xkcd.com/2931) ⁢ > > > > How is it possible that he neglected to include eclipses? ⁢ > > Not sure where on the chart it would go. I guess you could technically chase it, even though you already know the path. I just went through this last month. You’re trying to find the best viewing location that avoids cloud cover and obstructions (like trees) and crowds…and has available parking. Over the course of our drive north to the path of totality, I changed our intended viewing location three times because of clouds that were predicted to come in from the west. I was also on the phone (and texting) with a friend as we each drove north to Vermont and/or New Hampshire. Even though we started off in different states, we each ended up only five miles away from each other to see the eclipse. ---
**Author:** ![digs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/digs/32/14889_2.png) [@digs](https://boards.straightdope.com/u/digs)\ **Post date:** [May 15, 2024, 11:59pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3027 "2024-05-15T23:59:28Z")
> [@robby](#): > > Yes, I hate this too. I find myself silently screaming at the other drivers to: “TAKE YOUR RIGHT-OF-WAY!!!” It’s even worse when you’re on a bike and SO MANY times people slam to a stop, narrowly avoiding being rear-ended, just so they can wave the bicyclist across the road. Look, if I do, I’ll get creamed by the cars in the next lane who can’t see me, _and_ the do-gooder is holding up a line of cars (last time it was a dozen commuters trying to get home during rush hour). I’ve been known to yell "Go! _GO!_ You have _one_ job, _DRIVE YOUR CAR!"_ ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [May 16, 2024, 4:05pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3028 "2024-05-16T16:05:59Z")
> **[Elementary Physics Paths](https://xkcd.com/2933/)** > > ==COSMOLOGY==\> 'Uhhh ... how sure are we that everything is made of these?' Yes, it’s all “elementary”. /insane laughter ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [May 17, 2024, 11:26pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3029 "2024-05-17T23:26:16Z")
> [@thorny\_locust](#): > > Not all such roads have such heavy traffic that making a left onto them without a light is unreasonable. We watch dashcam videos and it’s a staple there, but usually someone stopping short to let a driver turn left into a driveway – who gets nailed by someone in the outside lane. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [May 17, 2024, 11:33pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3030 "2024-05-17T23:33:40Z")
> **[Bloom Filter](https://xkcd.com/2934/)** > > Sometimes, you can tell Bloom filters are the wrong tool for the job, but when they're the right one you can never be sure. Just tosave everyone the bother: > **[Bloom filter](https://en.wikipedia.org/wiki/Bloom_filter)** > > A Bloom filter is a space-efficient probabilistic data structure, conceived by Burton Howard Bloom in 1970, that is used to test whether an element is a member of a set. False positive matches are possible, but false negatives are not – in other words, a query returns either "possibly in set" or "definitely not in set". Elements can be added to the set, but not removed (though this can be addressed with the counting Bloom filter variant); the more items added, the larger the probability of false ... ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 17, 2024, 11:45pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3031 "2024-05-17T23:45:47Z")
I was _just_ trying to think of Bloom filters. I came up with [HyperLogLog](https://en.wikipedia.org/wiki/HyperLogLog), which is an entirely different kind of probabilistic data structure, intended to only _count_ the number of distinct elements in your set, and not determine if a specific element is in the set (though see now that Bloom filters are mentioned in the sidebar). Thanks, xkcd. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [May 20, 2024, 11:26pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3032 "2024-05-20T23:26:43Z")
> **[Ocean Loop](https://xkcd.com/2935/)** > > I can't believe they wouldn't even let me hold a vote among the passengers about whether to try the loop. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 20, 2024, 11:37pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3033 "2024-05-20T23:37:26Z")
That really deserves a _What If?_ I have zero intuition as to whether a stable loop of water that size is plausible. Though I am 98% certain that the outlet would completely scour the ocean floor and that it would have to be made of something much more sturdy than rock. ---
**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\ **Post date:** [May 20, 2024, 11:52pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3034 "2024-05-20T23:52:16Z")
Assuming that ship is 1000’, or 300 m, long (a typical large ocean cruiser), the radius of the loop is around 500 m. Using the simplistic equation for minimum speed needed to stay in the loop = sqrt(rg), you get 70 m/s, or 160 mph, at the top of the loop. That’s quite a current. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 20, 2024, 11:59pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3035 "2024-05-20T23:59:31Z")
That’s a start. But at this scale, you also need to account for the water slowing down due to gravity. A fountain would need to start at ~140 m/s to reach a height of 1000 m. That’s not purely additive with the other figure, but it’s definitely going to raise the threshold. ---
**Author:** ![Pleonast](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pleonast/32/1183_2.png) [@Pleonast](https://boards.straightdope.com/u/Pleonast)\ **Post date:** [May 21, 2024, 12:07am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3036 "2024-05-21T00:07:18Z")
It’s a modern take on [Charybdis](https://en.wikipedia.org/wiki/Charybdis). Not only will the output scour the ocean floor, but the intake would be catastrophic. I expect the waste heat from the power source would likely boil the water going through. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 21, 2024, 12:09am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3037 "2024-05-21T00:09:17Z")
> [@Dr.Strangelove](#): > > That really deserves a _What If?_ I have zero intuition as to whether a stable loop of water that size is plausible. It’s definitely not plausible. Since when has that ever stopped Munroe? ---
**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\ **Post date:** [May 21, 2024, 12:10am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3038 "2024-05-21T00:10:03Z")
> [@Pleonast](#): > > I expect the waste heat from the power source would likely boil the water going through. That’s easily solvable by putting it at the bottom of a waterfall. Route the flow into the loop and gravity will provide the initial velocity. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 21, 2024, 12:39am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3039 "2024-05-21T00:39:19Z")
I suppose it would have been more accurate to say _physical_. It’s perfectly ok to assume that the pump is powered by every power plant on the planet. But it’s not ok to ignore, say, the viscosity of water if it’ll boil while going around the loop. I’ll give a pass for assuming the loop is made from _scrith_ since the topic of interest lies elsewhere. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 21, 2024, 1:17am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3040 "2024-05-21T01:17:01Z")
Ah, I see what you’re saying. Though I don’t think there are any fundamental limits to how low the friction could be between the water and the walls of the loop. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [May 21, 2024, 3:03am UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3041 "2024-05-21T03:03:52Z")
It’s not just friction with the loop, though. If the water all started at the same (linear) speed, then the layer closest to the center will have a greater angular velocity than the parts farther from the center, since it represents a shorter distance. Ok, so maybe you can design the pump to output at just the right velocity for each layer… but gravity is slowing the water as it travels up the side, and that’s a linear reduction in speed, not a proportional reduction. So the velocity will mismatch again as it goes up the side. It will also bunch up somewhat since water is incompressible and the cross-sectional area times the velocity has to be constant. Maybe it’s possible to create a curve that accounts for this. But also, the water in general needs to have some angular velocity as it goes around. I don’t think there’s a way to do this without turbulence. There are just too many constraints on the solution. ---
**Author:** ![Norse](https://avatars.discourse-cdn.com/v4/letter/n/a9adbd/32.png) [@Norse](https://boards.straightdope.com/u/Norse)\ **Post date:** [May 21, 2024, 1:34pm UTC](https://boards.straightdope.com/t/xkcd-thread/854574/3042 "2024-05-21T13:34:59Z")
> [@Dr.Strangelove](#): > > I don’t think there’s a way to do this without turbulence. An ocean liner of 300m typically has a width of 60m and requires a depth of minimum 7.5 m - say that the depth of the water is 10 m. That gives the loop a [characteristic length](https://en.wikipedia.org/wiki/Characteristic_length) of 17.1 m. The [Reynolds number](https://en.wikipedia.org/wiki/Reynolds_number) will then be (1000 kg/m3 · 70 m/s · 17.1 m)/0.001 Pa·s = 1.2·10^9 Already at Re \> 1·10^5 we’re well into the tubulent flow regime. so yes: there will be some turbulence. [Previous page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=151) [Next page](https://boards.straightdope.com/t/xkcd-thread/854574.md?page=153)