Ask MetaFilter questions tagged with relativity

Special Relativity Question ;)

jfid1 — Mon, 21 Sep 2009 22:43:01 -0800

This one's for us physics nerds. - Is the speed of light our universe's only true constant? And does this explain why time dilation occurs most for extremely massive objects? - Does time dilation only occur when an observer is present?

Is heliocentrism wrong?

wigglin — Mon, 28 Apr 2008 02:26:06 -0800

Does modern science prove the theory of heliocentrism wrong? In 1990, in a defense of the church's actions toward Galileo, Cardinal Ratzinger references Marxist philosopher Ernst Bloch in order to demonstrate that the Theory of Relativity has proven heliocentrism wrong. Here is an excerpt:

According to [Ernst] Bloch, the heliocentric system – just like the geocentric – is based upon presuppositions that can’t be empirically demonstrated. Among these, an important role is played by the affirmation of the existence of an absolute space; that’s an opinion that, in any event, has been cancelled by the Theory of Relativity. Bloch writes, in his own words: ‘From the moment that, with the abolition of the presupposition of an empty and immobile space, movement is no longer produced towards something, but there’s only a relative movement of bodies among themselves, and therefore the measurement of that [movement] depends to a great extent on the choice of a body to serve as a point of reference, in this case is it not merely the complexity of calculations that renders the [geocentric] hypothesis impractical? Then as now, one can suppose the earth to be fixed and the sun as mobile.”

From here.

My question is purely about the science behind this statement and the rest of the commentary in Ratzinger’s article. Forget about whether the church should be persecuting scientists in the first place. I want to know, does modern science prove Galileo wrong?

The planets revolve around the sun. The reason why geocentrism makes bad predictions is because it is wrong. This is what I thought while reading this article, but as I have such a hard time understanding the theory of relativity, perhaps I am missing something or do not quite understand what Bloch is implying with his statements. I would appreciate it if someone with a better understanding of science could clear this up for me. Thanks!

A Problem of Scale: Halfway in size between an atom and the universe

0bvious — Sun, 18 Feb 2007 16:10:04 -0800

"A human is halfway in size between an atom and the known universe"... This is a paraphrased quote I have come across several times. I like it. Who said it first? How true is it in the most literal sense? And, finally, what errors arrive in postulating a universe, or an atom, which can be measured AT ALL from our singular, relativistic, perspective? I found this quote from Cosmic Evolution which further complicates the whole relative size issue:

"Roughly halfway in size between an atom and a human, the amoeba has poor awareness and coordination. It generally responds only at the point stimulated, communicating the information sluggishly through the rest of its body. Although amoebas have developed a crude nervous system, living things that aspire to be more agile—and smarter—surely need quicker internal reactions." - link

Kind of sets another stage from which to view this question.

I also found this quote from Holmes Rolston which further complicates things:

"The human world stands about midway between the infinitesimal and the immense. The size of our planet is near the geometric mean of the size of the known universe and the size of the atom. The mass of a human being is the geometric mean of the mass of the earth and the mass of a proton. A person contains about 10²⁸ atoms, more atoms than there are stars in the universe. Such considerations yield perhaps only a relative location. Still, questions of place and proportion arise." - link

Who first made this often used statement? My earlier questions still stand :-)

Thanks...

ABC's cancelled show, Relativity

evariste — Tue, 12 Sep 2006 22:18:54 -0800

Remember the ABC show, Relativity, with Isabel and Leo? God, I loved that show. It was so romantic and sweet! I just spent an hour Googling just to try to remember what it was called, until I finally figured out it was called Relativity. Sadly, Amazon implies that waiting for the release of a DVD is basically futile, as the studio is uninterested.

Hypothetically speaking, if I wanted to tell a friend how to download, legally or shadily, the 17 episodes that were made before its untimely cancellation, where would I tell him to look? Ahem. The "friend" in question already looked on Amazon, iTunes, the Pirate Bay, and Usenet-without much luck at all.

I would really like to see this show again, it was so good.

Gravity and relativity.

grahamwell — Tue, 28 Mar 2006 02:47:18 -0800

If General Relativity is accepted as true, why do Physicists talk about (and look for) Gravitons? My confusion here is that the two approaches seem to be mutually exclusive - either gravity is a function of 'warped space-time', or it is a conventional force mediated by a particle. Can it be both? If so, isn't one explanation redundant?

If not, can I take it that researchers who talk about Gravitons, as in this bizzare press release, don't accept General Relativity?

A lot of questions here, I guess I'm really asking for a laymans account of how both approaches could be reconciled. Any good explanatory links as to the current thinking about gravity would also be appreciated.

Time dilation and relative speed

seanyboy — Tue, 13 Jul 2004 04:53:52 -0800

Time dilation and relative speed. If the speed we travel is relative to the thing we're travelling away from, then how does the universe know which of the two things is actually moving? (so time dilation can occur) Is there a known universal "zero-speed"? If so, at what speed is the earth moving, and would it make a difference to the time dilation depending on the direction a spaceship moved away from the earth?

Explain Theory of Relativity

xmutex — Tue, 06 Jul 2004 14:12:46 -0800

trying to get my head around special relativity filter: Can someone explain to me, in terms as devoid of mathematical formulae as possible, how something traveling less than the speed of light cannot be accelerated to the speed of light?

Quick, cheap poster of MC Escher's Relativity?

Orange Goblin — Tue, 16 Dec 2003 09:57:47 -0800

Ok, I want to get my friend a poster of MC Escher's Relativity. The catch is I need it by Sunday, and I can't afford to spend more than a tenner. Can anyone suggest anywhere either online or in London that I can get it?