# The Past Through Tomorrow **URL:** \ **Category:** Factual Questions\ **Created:** [May 3, 2000, 5:17pm UTC](https://boards.straightdope.com/t/the-past-through-tomorrow/18472 "2000-05-03T17:17:41Z")\ **Posts on this page:** 5\ **Page:** 3
**Author:** ![JonF](https://avatars.discourse-cdn.com/v4/letter/j/cab0a1/32.png) [@JonF](https://boards.straightdope.com/u/JonF)\ **Post date:** [May 7, 2000, 10:27pm UTC](https://boards.straightdope.com/t/the-past-through-tomorrow/18472/41 "2000-05-07T22:27:22Z")
> [@](#): > > Last I heard relativity replaced most tenets of classical physics. I don’t see it all as a lego castle that you keep building, things do get thrown out when better things arrive. Care to mention a specific item that was thrown out because of Einstinian relativity? Some concepts were certainly modified, but I can’t come up with anything that was discaarded. (I believe that the notion of ether was essentially discarded before relativity but … there’s some concepts being played with today that are suspicously like ether). Newtonian mechanics, for example, is alive and well and in daily use; relativity just defined the rare cases when we _can’t_ use Newtonian mechanics. ---
**Author:** ![HorseloverFat](https://avatars.discourse-cdn.com/v4/letter/h/8e8cbc/32.png) [@HorseloverFat](https://boards.straightdope.com/u/HorseloverFat)\ **Post date:** [May 8, 2000, 1:25am UTC](https://boards.straightdope.com/t/the-past-through-tomorrow/18472/42 "2000-05-08T01:25:03Z")
I’m under the impression many calculations are easier with classical physics as compared to using relativity which are much more complex. No, I don’t buy the add on/slight change explanation, where’s the remains of say Aristole’s physics in todays science? ---
**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 8, 2000, 5:06am UTC](https://boards.straightdope.com/t/the-past-through-tomorrow/18472/43 "2000-05-08T05:06:10Z")
Aristotelian physics is still alive and well, and useful in certain circumstances. If I stand ofer on the left side of my desk and push, it’ll move to the right, just like Aristotle said. If a strong person throws a baseball (or a discus or whatever Aristotle would have thrown), it goes farther than if a weak person had thrown it. Unfortunately, old Unnle Ar wasn’t too big on math, so if you want a numerical answer, you’ve got to step up to, say, Ptolomaic physics, or Gallilean physics, or Newtonian physics, or Einsteinian physics. But if all the old physics were thrown out whenever a new idea came along… Sheesh, can you imagine trying to do a Lorentz transform every time you stepped on the gas in your car? ---
**Author:** ![KP](https://avatars.discourse-cdn.com/v4/letter/k/a9adbd/32.png) [@KP](https://boards.straightdope.com/u/KP)\ **Post date:** [May 8, 2000, 8:17am UTC](https://boards.straightdope.com/t/the-past-through-tomorrow/18472/44 "2000-05-08T08:17:09Z")
> [@](#): > > Care to mention a specific item that was thrown out because of Einstinian relativity? The notion of simultaneity? Under Newton, nothing was more fundamental. Under Einstein, it’s meaningless. The concept of uniformly _measurable_ time? Of Fixed distance? Point blank, you can’t even do Newton’s math without those assumptions. And they are gone, gone, gone in relativity. Sure, Newton gets very similar answers under 'ordinary conditions, but that’s irrlevant. It’s like the last post, which said Aristotlean physics is still alive and well. No it isn’t. Aristotle offered a set of explanations, which would fall apart to even a modern layman. We forget that Aristotle felt _X is true_, not X is kinda sorta true, if you squint just right. Eliminate the explanations (which is the entire point) and both Newton and Aristotle were saying “rocks fall”, which misses the whole point. Example: Fitzgerald deduced (as did others) the equations for metric contraction (and therefore time dilation etc.) long before Einstein. They deduced them algebraically, as unexplained fudge factors to explain why the Michaelson-Morley experiment (amont other things) failed. But they had no explanations, so the equations were meaningless, in both senses of the word - useless and without ‘meaning’. > [@](#): > > Sheesh, can you imagine trying to do a Lorentz transform every time you stepped on the gas in your car? No, and if I had to take a square root or logarithm for most integers, I’d use an approximation, too (especially of I’m doing math in my head. How many times have you used 3 as a rough estimate of Pi? No prob, we all do. But the guy who tries to say it _IS_ pi is wrong and more importantly, is missing the whole point of Pi. Aristotle said things floated because it was their intrinsic nature – and for centuries scientists were very unhappy with how it should be the nature of stone and wood to fall, yet wood floated. (this was debated long after Archimedes) Newton said something very different, but the boatmakers thought Newton was just Archimedes with math. ---
**Author:** ![JonF](https://avatars.discourse-cdn.com/v4/letter/j/cab0a1/32.png) [@JonF](https://boards.straightdope.com/u/JonF)\ **Post date:** [May 8, 2000, 11:05am UTC](https://boards.straightdope.com/t/the-past-through-tomorrow/18472/45 "2000-05-08T11:05:25Z")
I still contend that scientific theories were _extended_ rather than replaced by relativity. Aristotle’s theories were not part of the accepted scientific “wisdom” in the late 1800’s. > [@](#): > > The notion of simultaneity? Under Newton, nothing was more fundamental. Under Einstein, it’s meaningless One could argue that simultaneity was not the most fundamental concept in Newtonian mechanics, but there’s a flat-out error in that statement. Simultaneity is {b]not\*\* meaningless in relativity. Simultaneity is meaningful and defined for events that are time-like separated, which are the vast majority of the events we encounter in everyday life and scientific investigation. > [@](#): > > The concept of uniformly _measurable_ time? Of Fixed distance? Point blank, you can’t even do Newton’s math without those assumptions. And they are gone, gone, gone in relativity. > > Sure, Newton gets very similar answers under 'ordinary conditions, but that’s irrlevant. Yes, those concepts must be discarded in relativistic mechanics. But you can’t do Newtonian calculations without them. And the fact that Newtonian mechanics get very similar answers, indeed answers that are indistinguishable from the ‘real’ answers, under ‘ordinary conditions’ is incredibly relevant. Because of that fact, people can and do use Newtonian mechanics every day. This includes people launching some artificial satellites, engineers calculating forces and motions, scientists doing experiments that do not require relativistic corrections, and Lord knows what else. If Newtonian mechanics were discarded, then we’d be using relativistic mechanics in all those calculations. It was known long before Einstein that Newtonian mechanics are not a fundamental explanation of what really happens; Newton realized that his equations implied instantaneous interactions, and was at least uneasy about that and (I forget for sure) may have said that there must be something more that his model did not take into account. Several people (Pascal?) mathematically proved that Newtonian mechanics could not be fundamentally true. But the equations give the right answers 99.99999% of the time, and they are still a useful part of science. I suppose it may be a definition of semantics. I am assuming “discarded” means “no longer used”; you may have some other meaning. I the sense in which I am taking the word, nothing was discarded. [Previous page](https://boards.straightdope.com/t/the-past-through-tomorrow/18472.md?page=2)