# "Zero" frame of reference

1. Dec 31, 2014

### PWiz

Alright so I'm still trying to get a hang of the theories of relativity, and this thing has really been bugging me.
All forms of motion (and sometimes even physical observations) are defined for a particular local frame of reference. But is there any "stationary" frame of reference in the universe? By this, I mean a frame which is "truly at rest", and from which all relative velocities are equal to the "true" velocities, a frame which is the "zero frame"(Globally considering spacetime). I don't know if I'm making myself clear here, but since every quantity is measured from a "zero" reference (eg: electric and gravitational fields have zero potentials at a hypothetical point that is infinitely far away), it seems only natural that frames of reference for motion should also have a zero point(hypothetical or real). I read somewhere in quantum physics that just because something isn't observable doesn't mean it hasn't happened (and then read something about planck time and it being the minimum interval of time in which something is observable), so even though a galaxy seems to be moving at a velocity $x$, it's "true" velocity could be $y$ (which we have no way of knowing unless we have a stationary reference frame). It's just like saying that if you're in dead space in an astronaut suit with nothing around you for reference, it is impossible to say if you're in motion or not.

And if this is possible, then can there be a "universal standard reference"(again hypothetical because thinking of a real standard 0 for every existing thing in the universe seems impossible) for which all physical observations which are made are the "true" values? (Sounds something related to singularity) Since the entire universe runs on conservation laws, then it's safe to say that regardless of any changes that might occur in the universe, if such a global reference point were to exist, it would stay constant.
(I probably haven't explained it in the best possible way but I'd really appreciate if you could spend some time thinking about this)

2. Dec 31, 2014

### Doug Huffman

A hypothetical preferred reference frame is that with equal CMB temperatures from all directions.

3. Dec 31, 2014

### PWiz

But where's there energy (probably left from a few billion years), then don't we have the probability of matter spontaneously appearing and just increasing the entropy of the universe? (I'm in high school but I'm trying my best to be realistic, so don't expect me to be very familiar with metric tensor formulas )

4. Dec 31, 2014

### ghwellsjr

Even if you want to speculate that such a "universal standard reference" exists, it would be less work to pick an Inertial Reference Frame that is stationary with respect to you.

5. Dec 31, 2014

### PWiz

@ghwellsjr It would be less work, but it wouldn't solve the problem of "relative" and "true" velocities. Since most humans are on Earth right now, it seems like a good idea to let our position be the "0", but it wouldn't work globally(if in the future we inhabit a far off planet, then will we not have disputes regarding the motion of objects in spacetime?). There has to be a zero which can always be used. Like I can always use the hypothetical "infinity" point for defining a "0" in field potential, regardless of my position configuration in the field. The problem with a stationary frame "standard" is that it would vary according to my reference, instead of my reference depending on the "standard". Hypothetical points have the advantage of always being independent of our observation/position and yet being entirely sufficient in taking "actual" measurements.

6. Dec 31, 2014

### Staff: Mentor

No, there is no such thing, at least not if GR is correct. Experimentally, various "preferred frame" effects have been tested for, and none have been found, so our best current information is that GR is correct.

No, there doesn't. This only works in some cases. See below.

Not if there is no "infinity" point. For example, there isn't in the universe as a whole, so the concept of "field potential" can't even be defined for the universe as a whole.

7. Dec 31, 2014

### PWiz

@PeterDonis But doesn't every Physics textbook still define the point "infinitely far off" for the universe as a whole? I mean all the field potential formulas are calculated using "infinity" as one of the integral limits(with the assumption that it's part of the universe,because, well everything is). If we're mathematically defining "infinite" integrals for deriving formulas applicable in the universe as we know it, then I don't see the problem in qualitatively describing "infinity" for a standard frame.

8. Dec 31, 2014

### phinds

No, there is not. as Peter has already said. This horse has been beaten to death here MANY times. You are hardly the only one who WANTS for there to be, but wanting does not make it so. Get over it and move on.

9. Dec 31, 2014

### Staff: Mentor

No. This is exactly what the first postulate says does not exist.

10. Dec 31, 2014

### Staff: Mentor

That is not a preferred reference frame in the way the term is used in physics. In other words, in physics a "preferred" frame would be one where the laws of physics had a different form. The laws of physics are no different in a frame with isotropic CMB temperatures and non-isotropic CMB temperatures.

11. Dec 31, 2014

### PeroK

What you're missing here is a more formal understanding of mathematical "infinity" in terms of a "limit". One use of the limit is to give meaning to an "improper integral". For example:

$\int_{0}^{\infty}f(t)dt$

Is usually read as "the integral from zero to infinity". But to give it meaning, you need to see it as:

$\lim_{x \rightarrow \infty} \int_{0}^{x}f(t)dt$

So, when physicists talk about the value of a function at "the point at infinity", they are implicitly taking the limit of that function for increasingly large distances.

There is, in fact, no point at infinity, either physically or mathematically.

12. Jan 1, 2015

### Staff: Mentor

No. See below.

That's because those formulas are an approximation. They are not modeling the universe as a whole; they are modeling a single isolated system, like the Earth or the Sun or the solar system or the Milky Way galaxy, as if it were alone in the universe. For many purposes this works fine, since the effects of the rest of the matter in the universe, apart from the system being modeled, are negligible; for example, when calculating the orbit of a planet in the solar system, you don't need to take into account the gravity of Alpha Centauri or any other star, much less any other galaxy outside our own. But if you're trying to model the universe as a whole, you can't use these approximations, so the formulas you are used to simply don't apply.

13. Jan 1, 2015

### bahamagreen

It is kind of a tough thing to conquer conceptually. The foundations of even very "logical" ideas need very close examination.
The infinities are complicated... try this problem to get your foot in the door...

A lot of people encountering relativity immediately discover they have trouble getting past something like this:

If two objects are in relative motion, logically at least one of them must be in some kind of true absolute motion.
From the existence of true absolute motion, it follows that there must be an absolute true zero motion of absolute rest.

Think about that for a bit and see if you can break it apart. Maybe others could refrain until PWiz has had a chance to look this over and reveal the result..

14. Jan 1, 2015

### PWiz

@bahamagreen That is exactly what I'm asking when I talk of a "stationary" frame. All observed motions are relative because all frames of observation are in some form of motion as well. It follows that some point in the universe can be considered to be "truly" at rest, so all "observed" motion is the "true" absolute motion of that particular object. Eg: if two Helium nuclei (alpha particles) approach each other at 0.05c, then from a frame of reference of either particle, the velocity of the other nucleus is 0.1c, but from the frame of reference of a hypothetically stationary observer, the two objects are observed to be moving at their "true" velocity of 0.05c and -0.05c respectively. Note that from the frame of reference of either particle, it is impossible to state whether the frame itself is in motion or is stationary unless any other reference is visible (in this case the other approaching helium nucleus). If I'm in a train moving at 100mph and I see a bike moving at 40 mph on a road alongside the rail tracks, then since there is a certain relation of relativity between us, it is obvious that one is actually moving. If the bike were to be stationary universally, then the true velocity of the train is 60 mph.Likewise, if the train were to be "truly" stationary, then the bike's real velocity is -60mph (since it's moving away from the train). As has been pointed out to me in another thread, galaxies are "moving" apart at greater than light speeds, but that is obviously a relative velocity observed by us (since the Milky Way itself is also moving away). The problem is that there is no way to "confirm" whether an observer is stationary or not without any other reference, and no way to confirm the stationary nature of those references ,(sort of a paradox) therefore if there was a standardized "zero" frame (hypothetical or real), all motion observed from there would be the "true" motion (like how we designate the Earth to be a stationary frame of reference when observing velocities of meteorites approaching the surface, so instead of locally designating frames, if a universal zero reference were there, there would be no need to respecify the "stationary" frame for each new observation)

15. Jan 1, 2015

Staff Emeritus
Thed problem with that, though, is that while it might be a more comfortable way to think about it, the universe does not behave that way.

16. Jan 1, 2015

### A.T.

Why is that a problem?

17. Jan 1, 2015

### phinds

PWiz, it is really unfortunate that you are not able to get past this. As has been pointed out to you over and over, you are simply mistaken. As Vanadium just said, the universe just doesn't work the way you want it to.

18. Jan 1, 2015

### PeroK

@PWiz

I know you're still at school and you want to learn everything at once. Your posts are a mixture of SR, GR, Cosmology, Thermodynamics and QM, with ideas all jumbled up together. My advice is to focus on one thing at a time. Personally, I would tackle SR because it doesn't require advanced mathematics and, in the end, it is beautifully simple.

One thing I've noticed on this forum is that some people spend a lot of time trying to convince themselves of why an alternative theory isn't true. In my view it's better to focus on what is true; learn that; and, then, use your knowledge to explode myths and paradoxes. Doing it the other way round and wresting with the paradoxes and alternatives first seems a fruitless endeavour. You get people endlessly debating the twin paradox without learning SR. And, on the maths side, people endlessly claiming that 1/0 = $\infty$ without learning rigorous maths. It's a complete waste of time IMHO.

If you're clever enough you should be able to nail SR and derive enormous satisfaction from learning how the universe does work. And not worrying unduly why it doesn't work another way.

Happy New Year

19. Jan 1, 2015

### Staff: Mentor

No, it isn't obvious because it is not obvious that the term "actually moving" means anything. In fact, the first postulate states that it does not mean anything.

This forum is not a place for discussing personal theories. Thread closed.