Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Say you pick a point on the Earth. The earth spins at some constant $x (I don't know how fast, sorry). Now, that point has a different relative speed to a fixed point on Earth's orbit as it revolves around the Sun. This point also has a relative speed to the galaxy from a fixed observer, and etc down to an arbitrary point in the Universe.

How would you calculate the absolute/actual speed of this point from a theoretical relative point in the Universe traveling at constant speed 0.

Would this be considered the absolute speed on the universe that all objects should be compared against?

(I'm not a physics person really, just got into an interesting conversation with a buddy at work)

share|cite|improve this question

closed as not a real question by Malabarba, Marek, David Z Dec 26 '10 at 21:09

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

I'm posting an answer out of Christmas spirit, but I'm also voting to close. Sorry, this site is for questions graduate level and above. – Malabarba Dec 26 '10 at 19:49
I think that is unfair. I don't see why this site can't be used by people who are simply curious about physics. Also, 'graduate level and above' is a really high bar of entry and will shut out lots of students (like me) who are at college or University. I don't see anywhere on this site tat says questions are limited to graduate level and above. – david4dev Dec 26 '10 at 20:03
@david4dev: That's something that generates a lot of discussion, just start (or join) one in the meta if you'd like. I voted to close because the notion of absolute speed is one of the most basic things in a physics course. At the same time, it's also one of the most important, which is why I also answered. – Malabarba Dec 26 '10 at 20:14
@Bruce: actually, I think last we talked about it we decided also undergraduate and sophisticated high school questions are fine. But this one is neither, sorry @rublind. – Marek Dec 26 '10 at 20:20
@david4dev: as Bruce says, there are lots of discussions over at meta, go read them. Short summary: we don't want this site to be a place for too elementary questions. We want to enforce certain level of quality. Still, college students (especially inquisitive ones) are most certainly welcome! – Marek Dec 26 '10 at 20:24

The flip side of Bruce's answer is that any inertial trajectory that you select is an equally valid candidate for the "theoretical relative point in the Universe traveling at constant speed 0". That's the whole point Einstein kept going on about.

Nor---if the currently favored Big Bang cosmology is correct---can you locate (even in theory) a unique point which can be called the "origin" or "center" of the universe. The origin was everywhere at the same time.

share|cite|improve this answer

There are several problems with this:

  • There is the assumption that the Earth rotates at a constant speed. This is not true. For example, powerful earthquakes can change the speed of the Earth's rotation.

  • Everything is relative. You can, however, choose your '0' to be whatever you want but then your 'absolute' measurements would be relative to this.

  • The word 'absolute' suggests to me an exact measurement (I don't know if that was intended) but all measurements have uncertainty, even theoretically, as the act of observing will always affect the system you are observing.

This introduction to classical mechanics on YouTube may be helpful for understanding measurements further.

share|cite|improve this answer

The problem is: you don't have a point in the Universe traveling at constant speed 0, thus the entire proposal can't be done.

You could define a point (actually, a reference frame, but I don't think you know what it is) in the universe to have constant 0 speed. But then the so called "absolute speed" would just be the speed relative to that frame you picked arbitrarily, and wouldn't be absolute at all.

share|cite|improve this answer

Not the answer you're looking for? Browse other questions tagged or ask your own question.