>there actually is no objective answer as to which body gained and which lost energy! Energy is always conserved, but which way the transfer happened depends on your reference frame!
this isn't too difficult to demonstrate: pick an inertial reference frame A such that the spacecraft is at rest following the "collision" (aka the slingshot). In this frame, the spacecraft has 0 kinetic energy post-slingshot; therefore, it lost energy in the slingshot, which was transferred to the Sun. Likewise, pick a frame B such that the Sun is at rest after the slingshot (this would be the more usual frame to pick). In this case, it's the Sun that lost energy, and the spacecraft that gained it.
(depending on one's mechanics background this might appear anything from obvious to very weird and unintuitive)
That's correct, the energy comes from the body the spacecraft is slingshotting around (the Sun in this case). It's not mass or gravitational energy or anything weird like that, it's actually just a momentum transfer, the same as if the two objects had collided and bounced off each other elastically (i.e. without loss of energy to heat). So a (miniscule amount) of momentum (velocity x mass) is being transferred from the Sun to the spacecraft, and that's where the energy comes from.
(source: I studied physics and had a grandparent at NASA who worked on Voyager II and talked about this issue with me; but it's been a while since both of those things, so anyone with more fresh experience feel free to chime in!)
I'm studying physics right now, I can say I agree with everything you said.
One thing I'd like to expand on to those who don't know how greater energy means greater speed.
The kinetic energy equation is 1/2massvelocity^2=KE
Since the KE increases from the momentum transfer, and mass of the object stays constant, the only thing that can change is velocity, where it has to go up.
ex: KE=2, m=1
2=1/21v^2, v=2
Now if some momentum were transferred, and the kinetic energy increased to KE=8,
8=1/21velocity^2, velocity=4, since the mass can't change
i was wondering too! Do you think it might be because of citing family as a source? I barely ever post here, so don't have a good muscle memory for norms and best practices.
(also both scared and curious of what might result from dropping below 0 karma)
Is it though? A vehicle can't use a gravity-assist slingshot around the Sun to maneuver inside the solar system because the sun is at rest with respect to the rest of the solar system.
hey icehawk -- so you can use any celestial object in the solar system to maneuver; all you're doing is basically changing your direction. But you're right, there's something strange going on here. The original article doesn't actually have any information about what this spacecraft is doing, but it links to another one about the speed. I'm looking at that now, gonna add an addendum (or edit the old comment if i can figure out how to do that)
sorry kshacker, I may have thrown you off the scent here. My explanation of the slingshot effect is right, but it doesn't look like slingshotting is what the spacecraft is using to increase its speed:
tl;dr:
the spacecraft is just falling into the Sun, which is why it speeds up. It isn't gaining speed relative to anything else, and it loses that speed again once it flies away from the Sun. It is using Venus to get closer to the sun each time around by damping its angular momentum, which works but I don't know how to explain that in an ELI5 way.
so it's actually a little anticlimactic.
BlarfMcFlarf and pfdietz got this right below in their comment thread:
"What the Venus flybys did was not add energy so much as remove angular momentum. The hard part about getting close to the Sun is that conservation of angular momentum prevents it."
...and icehawk and vl correctly point out that you can't really use the Sun to increase your within-solar-system speed. Thanks to them for prompting me to look into this further. The cool slingshot maneuvers all involve planets, not the sun.
...but I think the key answer that none of us quite articulated to your question:
How is the spacecraft using the slingshot effect to increase its speed each time around?
...is that it isn't!
...the article dramatically describes it as "picking up speed" each time it goes around the sun, but that is misleading. It is just getting closer to the sun every time around, so of course it goes faster the closer it gets.
the cool part if any is how it uses Venus to get closer to the sun (by sapping angular momentum), but that's hard to explain in a nutshell and doesn't really relate to your energy question.
so that is hopefully now a better answer to this mystery that brings together what some of the other commenters have pointed out.
You're exactly right, I think, as to the reason most people are attracted to Myers-Briggs.
That said, it's odd that the narrative persists of M-B having been discredited, when, as the article mentions but doesn't explore, the opposite is true. Myers-Briggs traits strongly correlate with the categories in the FFA, which is the dominant model in psychology, as the article states. But this doesn't even include the cross-correlations between the 4 MB traits and the 4 main FFA traits (minus neuroticism)
Myers-Briggs is in fact basically identical to FFA but in a different eigenbasis, and minus the "neuroticism" dimension. This information is available in every major source on MB vs FFA, including just on Wikipedia. And yet, the "MB as horoscope" idea continues, despite having been scientifically discredited, so to speak.
the mapping is roughly this:
E/I <=> Extroversion
N/S <=> Openness
F/T <=> Agreeableness
J/P <=> Conscientiousness
But it is fun to make fun of the MB-scale (and its enthusiasts) as a horoscope and it's also fun to USE its categories as horoscopes, and the first meme feeds off the second, so both persist.
>That said, it's odd that the narrative persists of M-B having been discredited, when, as the article mentions but doesn't explore, the opposite is true.
What? The article directly says M-B has been discredited:
>In academic circles, however, the test has long been discredited. While the Myers-Briggs test lumps people into “types,” most modern personality tests measure traits on a continuum. Another objection rests on the test’s inability to predict meaningful life outcomes. “Basically, there isn't an algorithm that translates how people answer into how they're likely to behave,” explains Tomas Chamorro-Premuzic, professor of business psychology at University College London. Today, this is considered a crucial element of a personality tests. The backlash against the Myers-Briggs test has been powerful – beyond being shunned by academics, a steady drip of articles over the years have condemned its shaky scientific grounding. But this hasn’t stopped diehard Myers-Briggs fans seeing themselves within the test’s categories.
You're falling into exactly the same trap that horoscope enthusiasts have, gesturing to vague correlations and associations with no scientific grounding or basis.
I'm not sure what the best way to link a source on HN is, but I'll do my best.
McCrae and Costa did a study in the 1980s that looked at correlations between MB and FFA, as part of a larger, longitudinal study on aging. There were 468 participants.
As you can see, these are extremely strong, and the reason F/T and J/P are in the 0.40s is the cross-correlation I was mentioning, with part of the T/F prediction being tied to intra/extraversion (0.19), and part of the P/J prediction being tied to openness (0.30), which is intuitively just what you'd expect.
The full table of 16 correlations is available here:
McCrae, Robert R; Costa, Paul T (1989). "Reinterpreting the Myers-Briggs Type Indicator from the Perspective of the Five-Factor Model of Personality". Journal of Personality. 57 (1): 17–40
...so that's one of the sources for the correlations I mentioned, though there have been other such studies. But as I said, the strange thing is that this information has been publicly available and is even referenced on both the M-B and FFA Wikipedia pages (i.e that M-B and FFA are more or less measuring the same thing) and yet the popular narrative remains that one is dogma while the other is pseudo-science.
(and sorry, yes indeed, the article directly says M-B has been discredited, which is part of the point I'm making. It SAYS that, but it doesn't offer any support for that claim, and the only data it cites shows the opposite)
(edit: author does cite one source, a Vox article, which has the same problem of not citing any data and also plugs the FFA, saying "the newer, empirically driven test focuses on entirely different categories" which suggests the Vox author has also not delved into the research. Most of the people quoted in both pieces make statements like "[using the M-B] would be questioned by my academic colleagues," which may suggest the echo-chamber nature of the problem)
>yet the popular narrative remains that one is dogma while the other is pseudo-science.
Because it's not "the popular narrative", it's a factual statement. MBTI is unsupported pseudoscience while the Five-Factor Model is the more widely accepted model in psychology.
You seem fixated on the correlation point, as if that provides any validity to MBTI. For instance, you cite the study you mention being referenced on Wikipedia but ignore the numerous other studies cited in the lengthy section detailing the various criticisms and problems with MBTI. The article even opens with:
>Though the MBTI resembles some psychological theories, it is commonly classified as pseudoscience, especially as it pertains to its supposed predictive abilities. The test exhibits significant scientific (psychometric) deficiencies, notably including poor validity (i.e. not measuring what it purports to measure, not having predictive power or not having items that can be generalized), poor reliability (giving different results for the same person on different occasions), measuring categories that are not independent (some dichotomous traits have been noted to correlate with each other), and not being comprehensive (due to missing neuroticism).[10][11][12][13] The four scales used in the MBTI have some correlation with four of the Big Five personality traits, which are a more commonly accepted framework.
Your fixation on the correlation between the two models is noted, but MBTI otherwise lacks a valid scientific basis.
Again, you are simply wrong on the facts. MBTI is indeed pseudo-science, and selective use of sources doesn't change that. You keep trying to frame this as a popular misconception when it is simply the academic consensus.
The same professor says that criticism of the MBTI is overblown.
The article doesn't back up the claim that predicting meaningful life outcomes is considered a crucial element of personality tests. It also doesn't define meaningful life outcomes.
"What is elementary, worldly wisdom? Well, the first rule is that you can’t really know anything if you just remember isolated facts and try and bang ’em back. If the facts don’t hang together on a latticework of theory, you don’t have them in a usable form.
You’ve got to have models in your head. And you’ve got to array your experience—both vicarious and direct—on this latticework of models."
talk was previously linked from:
http://www.ycombinator.com/munger.html
but no longer available. Spent 20 minutes just now searching for it in frustration; here it is for anyone similarly afflicted!
no comments yet - how strange! seems like a major change, assuming he can follow through on it, which might be hindered by all the other stakeholders FB is beholden to. i have NEVER really used it for social engagement (ie always passively) so i won't notice any effect, but curious if it does make things substantially better
We have been trained by decades of marketing ploys that words like “less” or “more” mean pretty much that things will be better but ultimately the improvement will be oversold.
