Particle Trajectory & Velocity in Bubble Chamber vs HUP

In summary, the uncertainty in the particle's trajectory and velocity remains even if you measure delta_x and delta_p at different times.
  • #1
eoghan
207
7
Hi! Let's say I have a bubble chamber and a particle traveling in it. I know the trajectory of the particle, because I can see the bubbles. But if I measure the time elapsed between the appearance of the first bubble and of the last one, I know how much time the particle took to follow the trajectory. So I can know exactly particle's trajectory and particle velocity, but this is in contradiction with HUP... so, where am I wrong?
 
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  • #2
You are wrong because first you do not have a bubble chamber.
 
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  • #3
eoghan said:
Hi! Let's say I have a bubble chamber and a particle traveling in it. I know the trajectory of the particle, because I can see the bubbles. But if I measure the time elapsed between the appearance of the first bubble and of the last one, I know how much time the particle took to follow the trajectory. So I can know exactly particle's trajectory and particle velocity, but this is in contradiction with HUP... so, where am I wrong?

Well, this one is way off because you are measuring things at 2 different points in time. The HUP relates to knowing non-commuting observables simultaneously. The information you gained from measuring at T1 is no longer relevant after the measurement at T2.
 
  • #4
DrChinese said:
Well, this one is way off because you are measuring things at 2 different points in time. The HUP relates to knowing non-commuting observables simultaneously. The information you gained from measuring at T1 is no longer relevant after the measurement at T2.

It is a common misunderstanding. The uncertainty remains even if you take the delta_x and delta_p at different times.
 
  • #5
A fast particle travels about 30 cm per nanosecond, so will (did, actually) travel across the largest bubble chamber in about 10 or 15 nanoseconds. Visible bubble formation takes several milliseconds after the piston moves and the pressure on the hydrogen (or other liquid) is reduced to initiate bubble formation.
Bob S
 
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  • #6
Bob_for_short said:
It is a common misunderstanding. The uncertainty remains even if you take the delta_x and delta_p at different times.

Not sure I follow your thinking here. You can measure delta_x to any degree of accuracy at T1, and then measure delta_q to any degree of accuracy at T2. Maybe not in a bubble chamber though.
 
  • #7
I think you are talking past each other.

As Feynman pointed out in his lectures the HUP is about what we are able to predict. If we have a Gaussian wavepacket there is of course some uncertainty about predicting [tex]\Delta x[/tex] and [tex]\Delta p[/tex] at different times. However nothing will keeping us from backtracking for example by putting a position detector behind a long slit (assuring that the vertical momentum equals 0). You know the past pretty exactly, but you were not able to predict it.
 
  • #8
Cthugha said:
You know the past pretty exactly, but you were not able to predict it.
Knowing the past is even better than predicting.:smile:
 

Related to Particle Trajectory & Velocity in Bubble Chamber vs HUP

1. What is a bubble chamber and how does it work?

A bubble chamber is a device used in particle physics to study the trajectory and velocity of subatomic particles. It consists of a superheated liquid, usually hydrogen or a mixture of hydrogen and helium, that is kept just below its boiling point. When a charged particle passes through the liquid, it ionizes the atoms, causing them to release heat and form bubbles along the particle's path. The bubbles can then be photographed and analyzed to determine the particle's trajectory and velocity.

2. What is the Heisenberg Uncertainty Principle (HUP) and how does it relate to particle trajectory and velocity?

The Heisenberg Uncertainty Principle states that it is impossible to know both the position and momentum of a particle with absolute certainty. This means that in the bubble chamber, the exact trajectory and velocity of a subatomic particle cannot be determined simultaneously. The act of measuring one value affects the accuracy of the other, making it impossible to accurately measure both at once.

3. How does the HUP affect our understanding of particle behavior in the bubble chamber?

The HUP introduces a level of uncertainty in our measurements of particle trajectory and velocity in the bubble chamber. This means that while we can still gather valuable information and make predictions about particle behavior, there will always be a margin of error due to the limitations of the HUP.

4. Can the HUP be overcome in the bubble chamber?

No, the HUP is a fundamental principle in quantum mechanics and cannot be overcome. However, advancements in technology and techniques have allowed scientists to minimize the effects of the HUP and improve the accuracy of measurements in the bubble chamber.

5. How do scientists use the data collected from bubble chambers and the HUP to further our understanding of particle physics?

Despite the limitations of the HUP, the data collected from bubble chambers is still incredibly valuable in understanding the behavior of subatomic particles. By analyzing the patterns of bubbles and their trajectories, scientists can make predictions about particle interactions and properties. This data also helps to validate and refine existing theories in particle physics.

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