# Uncertainty by relativity

1. Jul 7, 2009

### ZacharyFino

is it possible that because position and velocity are both only values relative to another frame of reference they simply cannot both be precisely known on a small scale because neither has an absolute value.

2. Jul 7, 2009

### DrChinese

That really does not explain the Heisenberg Uncertainty Principle (HUP) - assuming that is your question.

The HUP applies to spin as well as position and momentum. That would strongly imply that relativity could not be a factor (since relativity does not say anything about spin). In addition, the HUP applies to entangled particles that are distantly separated: which would conclusively rule out relativity as a factor.

3. Jul 7, 2009

### ZacharyFino

i wasn't trying to explain HUP i was just saying that you cant expect to have a known value for two properties (position and velocity) whose values are always relative to an external frame of reference. a single particle in an empty universe cannot have a position or a velocity because both those values depend on an external viewpoint, what i was saying is that even with a frame of reference you still shouldn't be able to solve for both position and velocity because they are still both dependent values with no absolute value to offer each other, and if an equation is set up including values for each, it would be inferring that they both are absolute values which defies reality but can be used to determine probability. sorry if my question is unclear, im 14 years old and my vocabulary is limited. what im ultimately trying to say is to me it seems apparent that quantum mechanics ONLY determines probability functions and that it doesnt really explain why anything happens on a small scale

4. Jul 7, 2009

### diazona

Well yeah, that's true, but the rest of your post isn't making any sense...

5. Jul 7, 2009

### bucher

There is no particle that exists where the exact position or velocity is known. HUP is still an application to quantum mechanics. It's the reason why there is uncertainty in all values and why you cannot know two things about a small object with no uncertainty. On a quantum scale, all of the properties are mashed together and you can't determine one thing without making the other unclear.

All that this uncertainty does to a value is put a +/- after the value.

6. Jul 7, 2009

### ZacharyFino

i understand what the uncertainty principle states, but what im trying to say is that position and velocity being values ONLY relative to another reference point means that they cant be used simultaneously. Had an equation been set up including both values it would be obsolete as they are complementary variables.

7. Jul 7, 2009

### ZacharyFino

position isnt an actual property of an individual particle but a property of the locations of the particle and any other reference point.
velocity is only a property when the position is changing relative to another reference point.
it seems they are of the same property and mean absolutely nothing together.

8. Jul 7, 2009

### bucher

So are you debating the usefulness of position and velocity in quantum mechanics? I'm still not quite getting at what the question is. Could you give some sort of example where this may come up?

9. Jul 7, 2009

### ZacharyFino

im not debating their usefulness but rather their existence in reality as 2 different properties. i should have put this in a different section. neither velocity or position hold any absolute value, and in an apparently impossible way to explain, velocity and position have no true value when known together. i guess what i mean is that for a reason other than HUP, velocity CANNOT be known alongside position because they are both only properties of difference between themselves and an external frame of reference. however in my mind there seems to be a constant value missing and i dont want to find out that it is planks constant and ive been pondering over a math-less form of HUP. i would give some equations as examples but i know nothing of the sort being as im 14 and have no idea how to acquire the knowledge in an efficient way.

10. Jul 7, 2009

### ZacharyFino

imaginary numbers seem to be involved.......

11. Jul 8, 2009

### DrChinese

Welcome to PhysicsForums, ZacharyFino!

I applaud your knowledge of these points. You definitely should be encouraged to continue to question and learn in this field, you are off to a great start...

You can measure any single observable to any degree of accuracy desired (assuming experimental setup is suitable for same). The HUP describes the statistical relationship between pairs of non-commuting observables, and h is central to that. Relativity describes how the laws of physics change (or don't change) between observers in different reference frames, and c is central to that.

Neither principle can be derived from the other.

12. Jul 8, 2009

### Naty1

I agree, well done!!!!, it's a pleasure to have you here!

You have asked a rather fundamental question for which there may not yet be a perfect answer. You are already deep enough into theory to expose contradictions and uncertainties among various theoretical explanations.

You posted
thats a valid relativistic viewpoint and one to always keep in mind as explaining what we observe. But it may not be the ONLY view.

Is relativity ALWAYS applicable? Sometimes relativity conflicts with
quantum theory!

Here is a discussion which might interest you: Is spacetime smooth?