# Can Absolute Velocity be Measured?

1. Apr 4, 2012

Just a silly idea i have, please debunk it since i cannot figure it out:

The Thought Experiment:

Provided to us is a spacecraft equipped with a particle acceleration and detection systems.

The craft is set on a course where it would not be interrupted by any interstellar objects and cuts its propulsion systems for the entire duration of the experiment.

A stream of electrons are accelerated to a certain speed (let’s say 0.8c) in the particle accelerator. The mass of an electron in the stream is then measured when the electron stream passes, say, in the direction the spacecraft is traveling.

This measurement of electron mass when the electron stream passes in the direction the spacecraft is traveling is repeated for various speeds (0.82c, 0.84c, 0.86c, 0.88c and 0.9c). We then plot these values on a graph (e.g Figure 1). This graph represents the increase in mass of the electron at various velocities relative to the spacecraft.

(Figure 1)

The graph we obtained is then compared to the graph of:

(Figure 2a)

*9.10938215x10-31 kg is the rest mass of an electron

to see where it fits in. This can be achieved by comparing the change in gradients of both graphs. We then superimpose the graph we got (Figure 1) onto the graph of the equation of Figure 2a

(Figure 3)

We are now able to determine our velocity through spacetime in the direction the electron was traveling when it was measured by taking a point on the graph we obtained and subtracting the relative speed of the electron from its actual speed as reflected from the superimposed graph.

Example: In Figure 1, we measure the relative speed of the electron, W, to be say 0.8c. When we superimpose the graph, the point which contains W now reads off the new graph as X (lets say 0.83c), so we deduce that we are moving through spacetime at a velocity of 0.03c in the direction the electrons were traveling when their mass was measured.

This experiment is repeated where the mass of the electron is measured as it is traveling in various other directions to determine our absolute velocity through spacetime. The direction which yields the largest velocity will give us the absolute velocity of the spacecraft through spacetime.

Further Applications

The absolute velocity of the spacecraft through spacetime can be compared with the velocity of the spacecraft relative to the cosmic microwave background radiation (CMBR) reference frame.

If both velocities are the same, we can assume that the CMBR reference frame (and the black hole/object that gave birth to big bang) is/was moving at an absolute velocity of 0 m/s through space.

However, if both velocities were different, we can deduce that the CMBR reference frame (and the black hole/object that gave birth to big bang) is/was moving through space at a certain velocity.

This comparison would shed some light on the physical nature of the big bang itself, allowing us to eliminate a few of the seemingly infinite number of theories that surrounds the beginning of the universe we know today.

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2. Apr 4, 2012

### Staff: Mentor

Welcome to PF!

Without reading your post, I can tell you this: the question posed in the title is misguided in that it assumes that there exists such a thing as absolute velocity. Current theory holds that there is no such thing, so it is meaningless/wrong to ask if it can be measured.

3. Apr 4, 2012

### ZikZak

The experimental graph will always yield the graph of γm and nothing else, leading you to conclude a speed of zero every time, regardless of the spacecraft's velocity relative to other bodies.

4. Apr 4, 2012

### Mentz114

Yawn. There is no absolute velocity through spacetime.

You misunderstand the nature of the big-bang. The BB was the actual unfolding of space embedded in a 4-dimensional spacetime. At time t-zero, there was no space.

Imagine a balloon, whose surface is a 2-D space embedded in 3-D. Now try to imagine that the surface is a 3-D space embedded in 4-D. Just as the surface area of a balloon of zero radius is zero, so the volume of the embedded 3-D space was zero at t-zero.

5. Apr 5, 2012

1. There is no such thing as absolute velocity? Maybe I am using the wrong term, but what would you define the velocity at which *God (an observer external to this universe)* measures you travelling at?

If you accelerate (in your point of view) in one direction, time may pass slower for you but if you accelerate in another direction, time may pass faster for you as you are 'slowing down' in space. The point at which time dilation does not apply to you (except for gravitational time dilatation) can be considered a 'special' reference frame where absolute velocity and mass can be measured?

2. I know the most accepted theory holds that space and time exploded from the big bang, but I dun think that there is anything absolutely against space and time existing before the big bang.

Spacetime could have been seen to have exploded out from the singularity as the singularity had sucked so much in to begin with. In any case, comparing 'absolute velocity' to the CMB reference frame would mean something either way. Dun want to argue too much about this.

3. ZikZak, would the experimental graph be the same? IMHO, One of the parameters in the equation is the rest mass of the electron measured relative to you. If you were travelling, you would weigh the electron rest mass to be more. The experimental graph you obtain should be of the same shape but translated away from the original graph.

Thank again and have to GOOD Friday.

6. Apr 5, 2012

### PAllen

An observer outside this universe is not covered by science. You can posit anything you want - it is untestable, unknowable, and not subject to discussion in a scientific forum.

According to all known physics there is simply no such thing as absolute velocity - period; no qualifications or dancing around it. Any speculations otherwise should be pursued in a forum outside physicsforums (e.g. a religious forum).
This is complete nonsense, at odds with known observations. No matter what your state of motion or acceleration, time flows normally for you. It is true that for two clocks following different histories, one that never accelerates will show more time elapsed compared to one that accelerates away and back such that it meets the first clock. However, the direction this occurs in does not matter, nor does any supposed 'absolute velocity' of the non-accelerating clock matter.
No, completely false. Time dilation is relative. If Katy and Robyn are moving apart from each other at 90% of light speen, each concludes the other has a slower clock. If Justin is sees both moving away from him at the same speed, then he concludes both clocks are running slow. Further Katy determines Justin's clock is running slow, and Robyn's clock running even slower. Meanwhile, Robyn concludes Justin's clock is running slow, and Katy's even slower.
Your personal beliefs, not subject to publication of a research paper, based on data or analysis, in a reputable journal, are not a proper subject for discussion in physicsforums. Note, we are not called 'idle speculation forums without understanding or knowledge'.
Forgetting absolute velocity as the nonsense that it is, you can measure velocity relative to CMB. Either the frequency of CMB is isotropic or it is not. If it is not, the degree of anisotropy measures your velocity relative to CMB radiation. This is cosmologically interesting, but it is not an absolute velocity. It is similar to noting that velocity relative to galactic center is interesting.
More complete nonsense. Let's clarify. If one particular observer is accelerating the electrons, then some other observer moving relative to the first will detect anisotropies consistent with their motion relative to the first observer. Similarly, if this second observer accelerates electrons, the first observer will detect anisotropies consistent with relative motion. There will be no observation that can distinguish which one has absolute motion, or even which one has motion relative to some third observer.

You are just throwing out purported observations that are contradicted by experiment, and by the most elemantary understanding of relativity.

7. Apr 5, 2012

### Staff: Mentor

This is undefined. He can measure whatever speed he wants (less than c), depending on the inertial frame he chooses.

No. For you, time passes with 1 second per second on your clock. And if you compare your clock with another one, only the relative velocity is interesting. And this comparison will be symmetric - both see that time passes slower at the other ship.

You can find an inertial system where the CMB has no dipole moment. But in terms of the laws of physics, there is nothing special about this system.

It would.
Note that different observers can measure different particle energys (and therefore different relativistic masses (I don't like this word)).

Welcome to the concept of "relativity" ;).

8. Apr 5, 2012

### Staff: Mentor

Sorry - yes, you are defining it properly, but no, it doesn't exist.

9. Apr 6, 2012

### spikenigma

There is , of course, no such thing as absolute velocity.

An interesting thought, however, is a spinning cylinder in space and an observer flying past, parallel to it's spin with no acceleration. Everyone in the universe (even in an empty universe) will agree that the cylinder is spinning at x velocity.

The observer can say "I am 5x away from it's moving point at an exact 180 degree angle...I am 4x away from it's moving point at an exact 180 degree angle...I am 3x....etc...

Thus since it is moving with me and everybody agrees that it is moving, I am moving also."

10. Apr 6, 2012

### HallsofIvy

That's because rotational motion is an acceleration.

11. Apr 6, 2012

### spikenigma

Yes, but philosophically the non-accelerating traveler can say.

" Everybody agrees that this accelerated point on the frame is moving, I am moving along the x-axis with it, thus I am moving. "

12. Apr 6, 2012

### phinds

:rofl:

Nicely put ! It's too bad some of the newbies don't get that before posting.

13. Apr 6, 2012

### Whovian

No, not everyone agrees that the accelerating point on the frame is moving. As far as I can tell, what you're saying is that if something is accelerating, then it's moving.

This is completely incorrect. Throw a ball straight up. At the peak of its toss, it is not moving. However, it is still subject to gravity, so it's still accelerating. Now, nothing can stay umoving for finite time when it's subject to acceleration.

14. Apr 6, 2012

### Naty1

The CMBR is simple one convenient reference frame for comparing measurements. Nothing unique, nor special, nor 'one a kind' frame. Everyone who makes measurements, unless at the same point in time and space, generally obtains different results because space and time vary from point to point in spacetime. We can convert measurements, that is 'transform', from one spacetime point and set of coodinates to another, but yours will be as good as mine as good as every one of the other infinite number of available spacetime points. No frames are special.

15. Apr 8, 2012

### Austin0

I would think that as soon as it leaves your hand it is in inertial motion ; freefall. As such there is obviously no point of no motion until it returns to your hand. That is an illusion. Like Zenos arrow.
Based on an abstract dimensionless slice of time that does not apply to real world physics. Zeno's point in creating the paradox.
On the other hand sitting motionless on the ground is a state of acceleration so you're right, not everyone agrees acceleration necessarily implies motion.

Last edited: Apr 8, 2012
16. Apr 8, 2012

### Bjarne

There is no absolute velocity, because c (and maybe everything else) always looks the same for all observers (so fare I have understood).

But this is not the same that there is no absolute motion direction.

We can for example be moving the same or the opposite direction as the Milky Way, and at a larger perspective, the same or the opposite way as the local cluster, and if we one day will reach a larger perspective, for example multi universes moving relative to each other, - we can also be moving the same or opposite way relative to our Universe….etc..

I either cannot see the “problem” or any limit to that absolute motion not should exist.

That out perspective is limited , cannot be the same that an absolute motion perspective not exist.

17. Apr 8, 2012

### Naty1

unsure just what you last post says....

but with Newtonian mechanics, the relative velocity is independent of the chosen inertial reference frame. Time and space are the same everywhere. All frames are the same.

This is not the case anymore with special relativity in which velocities depend on the choice of reference frame. Time and distance vary in different partsof spacetime; any frame is as good as any other; different frames give different results.

18. Apr 8, 2012

### Staff: Mentor

No, that is not possible, unless you define an arbitrary inertial system in which you want to make this statement. The only physical thing is our velocity relative to the Milky Way, like "we are moving towards the center with 500km/s".

And that is even "more undefined", as different universes (with common meanings of the word) are not connected in space. You cannot even quote a distance between universes, as there is no space to measure the distance in it.

19. Apr 8, 2012

### Bjarne

It can also be relative to the center of a cluster of galaxies

20. Apr 8, 2012

### yuiop

If we take the velocity of the ball 1 second before the apex and the velocity of the ball one second after the apex then the average velocity over that 2 seconds is zero. We can reduce that 2 seconds to as small an interval as we like and still obtain an average velocity of zero. This is part of the slight of hand of how calculus works. Certainly we can set dr/dt = 0 in the equations of motion of a tossed ball and obtain a sensible answer for when the ball arrives at apogee without obtaining any infinities or undefined answers. Mathematically there is a point of no motion for an accelerating ball in free fall. However, you are right that Zeno's arrow paradox argues against this and basically he argues that there is no such thing as a "instant of time". More recently Peter Lynds made a similar point in a published paper. Personally I believe we will end up with a theory of physics that is based on granular quantum time but currently we have no such theory and time is infinitely divisible.

As far as the CMBR, I hope the OP is aware that two observers separated by billions of light years could have a relative velocity of say 0.9c with respect to each other and yet both be at rest with their local CMBR in the expanding universe so there is no absolute sense of who is moving or who is stationary even when the CMBR is taken into account.

21. Apr 8, 2012

### Whovian

Wait. I thought the derivative got rid of Zeno's Paradox.

The post I was replying to basically assumed, from what I gathered, that in all inertial reference frames, an accelerating object is moving at all points in time. I was trying to find a certain reference frame with a certain time that this didn't hold. (Note that gravity complicates things a bit, but we can move back to the reference frame of the ball and see the velocity of the observer, which is 0 at a certain point.)

Wait. One small thing. Sitting on the ground isn't an inertial reference frame.

Note, again, that having acceleration but no velocity cannot persist for any extended period of time.

22. Apr 9, 2012

### Austin0

The ball is subject to acceleration through the whole course from the hand and back.
So according to your next statement; it can not stay unmoving for finite time through that whole time while it's subject to acceleration.
Finite time is the key. As long as the time duration is non-zero (finite) there will be movement. It is only when you consider an instant (interval with no duration) that there is no motion. Like a snapshot with a camera with an infinitely fast shutter speed. But then anything in motion is motionless for that instant. That is the basis of Zeno's arrow paradox.

I think you must be referring to Achilles and the tortoise. A reductio ad absurdum argument against thinking the mathematical concept of infinite divisibility of a line, applied to the real world.
The irony is that, for thousands of years after, many mathematicians failed to get the joke [see the point] and seriously tried to solve the puzzle and mathematically justify the real world result. I.e Achilles does catch up with the tortoise.

Another example is the abstract concept of a dimensionless mathematical point.
When applied in the real world in the form of a point charge in electrostatics, it produced Zenoesque calculation results (infinities) and required renormalization. In effect assigning it a finite dimension.

One small thing Note above where I said sitting on the ground is an accelerating frame.
No disagreement.

23. Apr 9, 2012

### Austin0

1) AN average velocity of 0 over a course does not necessarily imply any interval of 0 velocity at any point in that course

2) More importantly it definitely doesn't imply no motion.

Would you agree that many of the tricks of calculus ,like limits , provide exceedingly useful and accurate approximations?
SO yes; as dt ---->0, dr ----->0 and v ---->0 but it is only at dt=0 (dimensionless instant) that v=0
Yes you can find an accurate figure for when the ball reaches apogee dta.
And an equally accurate figure for when the ball will then return to the initial point dti if you add them together and subtract the sum from the time for the whole course dtc - (dta+dti) = what do you get?
0 time actually at apogee ,right???
For the ball to actually be motionless at this point in space would require a finite time interval spent at this exact location. Which would require an external acceleration/force, anti-gravity or magic.

24. Apr 9, 2012

### yuiop

I agree with this 100%. Mathematicians have failed to get the point of Zeno's paradoxes which for the most part demonstrate that if time and space are infinitely divisible, as mathematicians assume, then the world simply would not work the way we observe it does. Slowly and quietly the revolution is taking place and Zeno type effects are being taken seriously in particle physics at the quantum scale involving virtual photons etc. I believe if we eventually arrive at a quantum theory of gravity that supercedes GR, then mathematicians might finally get the point and Zeno will be vindicated. Until then, calculus says the velocity of a particle at apogee is zero.

25. Apr 10, 2012

### GeorgeDishman

The error in Zeno's Paradox is that he implicitly assumes that the sum of an infinite series must also be infinite, Achilles cannot catch the tortoise in any finite number of steps, i.e. on a graph plotted with equal x-axis increments representing a halving of the separation, the point at which they meet cannot be plotted. In a sense it has a parallel in GR and cosmology in that some coordinate schemes do not cover the whole of a manifold.