Saturday, June 09, 2007

Bad Physics

It is often amusing when people who are writing an article that has nothing to do with physics, tries to either justify, or make some similar comparison, to something in physics. The article titled "Obama Physics" was one such example. This is another one.

This article talks about "parthenogenesis", that deals with how species reproduce. I certainly am not an expert in it, but I find this paragraph to be rather amusing and a chance to illustrate this concept in physics clearly to people who do not understand it:

For explaining everyday life—babies, puppies, puberty—the mommy-daddy story of procreation works fine. But at life's edges, conventional biology, like conventional physics, breaks down. As you approach the speed of light, time slows and distances shrink. And as you approach extinction, genes find new ways to pass themselves on. Scientists call it "reproductive plasticity." A Komodo dragon manufactures a mate. A shark's got to do what a shark's got to do.


I think of all the consequences of Special Relativity (SR), this part is one of the most misunderstood by the general public.

1. Conventional physics does not "break down" as one approaches the speed of light. this is because SR IS a part of "conventional physics". Maybe this author meant "classical physics". It is misleading and wrong to not include SR within conventional physics. Stating it as it is gives the impression that physics simply doesn't work close to c. This is absolutely wrong.

2. Time doesn't slow down when one approaches c. This is a very popular misconception. The principle of time dilation requires TWO OBSERVES IN DIFFERENT INERTIAL FRAMES. Let's say B is moving with respect to A. If A looks at B's clock, A will see that B's clock is moving slower. However, B can also say the same thing, since we have no preferred frame. B will see A's clock also moving slower. HOWEVER, neither A nor B will see THEIR OWN CLOCK as being slow. The time interval in their own frame doesn't change! So even if B is moving close to c with respect to A, B will NOT see its time slowing down. It will see A's time slowing down! So what is stated in the article is utterly wrong.

Again, I'm sure this is just nitpicking, but it is surprising how many people who don't normally read actual physics texts would get a lot of their understanding of physics via articles like this. At the very least, someone using something in physics to illustrate their point should pay a bit more attention on the ACCURACY of what they are writing.

Zz.

5 comments:

YS said...

Calm down. As you see from his biology example, by "conventional physics" he just means "everyday physics".

Also, it's not necessarily wrong to say that if you're moving close to the speed of light your time goes slower. Take a fast airplane, and go fly for a while. When you come back we compare clocks and see that yours went slower.

ZapperZ said...

That isn't quite right, either. SR is a part of conventional, "everyday" physics. Example: GPS. It is no longer "exotic" at all. So no, it is incorrect to consider conventional physics or everyday physics to not include SR.

And in your example, you have to include accelerating effects, i.e. you speed up, slow down, and then compare clocks. This is a more complex application of Relativity than a simple time dilation effect that I believe the author was trying to illustrate based just on what was written. Furthermore, while you undergo such a motion, you STILL have no indication that your clock is slowing down. It behaves "normally" as far as you can tell. All you can do is that after you get back to the original reference frame, you make a comparison in that frame with a clock that you have synchronized with in the first place. Again, such intricate details are not normally considered or are known by many who do not study Relativity in detail.

Zz.

Stupac2 said...

No, you're not nitpicking. What the author wrote was just plain dumb. Why pick SR and not quantum gravity, where physics actually does break down?

YS said...

Most people, including myself, don't know how exactly GPS works. The method of operation of GPS is therefore not a part of what we know from everyday physics. Even people who do know roughly how GPS works won't usually include special relativity in their explanation.

ZapperZ said...

Well then, you and "most people" probably might want to make sure they read this to understand how prevalent Relativity is in our everyday lives.

http://www.physicscentral.com/writers/2000/will.html

Zz.