How to intuitively think of translations and Galilean boosts commuting?

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In summary, the concept of translations and Galilean boosts commuting can be understood through the lens of symmetry in physics. Translations refer to shifts in position without altering the object's state, while Galilean boosts involve changes in an object's velocity. When both operations are applied sequentially, their order does not affect the final outcome, indicating that they commute. This property reflects the underlying symmetries in space and time, emphasizing that spatial translations and uniform motion can be treated independently in classical mechanics. Understanding this relationship aids in visualizing and solving problems related to motion and reference frames.
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binbagsss
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how to think of translations and Galilean boosts commuting intuitively
 
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How fast something is going and in what direction doesn't depend on where you are.
 
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Depends on your definition of intuitive, but if a translation is T(X) = X + A and a boost is B(X) = X + Vt, then TB(X) = BT(X) = X + Vt + A because addition commutes.
 
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Moderator's note: Thread moved to the Classical Physics forum since that is the proper context for discussion of Galilean boosts.
 
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binbagsss said:
translations
Note that this has to mean spatial translations for your statement in the OP to be true. Galilean boosts and time translations do not commute.
 
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One builds intuition by working through problems. There is no magic trick to it.
 
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Imagine yourself in a car. You press accelerator pedal (this is boost), then you wait for some time (=time translation). Obviously, after these two transformations you'll find yourself far from the place you've started from.

In reverse order: You wait for some time (=time translation), then you step on accelerator (=boost). You have not moved.

Conclusion: time translations and boosts do not commute.
Eugene.
 
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meopemuk said:
press accelerator pedal (this is boost)

How?
 
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By definition, boost is a transformation that changes velocity of reference frame.

When I press accelerator pedal, velocity of my car changes. Then the inertial reference frame associated with me and my car experiences a boost.

Eugene.
 
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meopemuk said:
By definition, boost is a transformation that changes velocity of reference frame.

When I press accelerator pedal, velocity of my car changes. Then the inertial reference frame associated with me and my car experiences a boost.

Eugene.
During the acceleration itself you're not experiencing what physicists would call a 'boost'. Inertial observers are connected by 'boosts'. During acceleration you're not an inertial observer.
 
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meopemuk said:
By definition, boost is a transformation that changes velocity of reference frame.

No, boost changes inertial reference frame to a different inertial one.
 
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  • #13
weirdoguy said:
No, boost changes inertial reference frame to a different inertial one.
True, during acceleration I am not an inertial observer. But after I released the accelerator pedal, I move with a constant speed and I may regard myself as an inertial observer, which is boosted with respect to my previous state.

I agree that this is not a perfect analogy for boost, but not a bad one if we disregard the (short) time during which I am stepping on the gas pedal.

Perhaps, a better analogy would be to jump (mentally) to another car that passes nearby.

Eugene.
 
  • #14
haushofer said:
Actually, they don't commute in the Bargmann algebra :P See e.g.

https://arxiv.org/abs/1011.1145
From the abstract I see the Bargmann algebra is assoicated with the centrally extended Galilean algebra. Could you give, very briefly, implications of what this means compared to the question I asked which was on, what I assume can be referred to as the unextended Galilean group. thanks
 
  • #15
PeterDonis said:
Note that this has to mean spatial translations for your statement in the OP to be true. Galilean boosts and time translations do not commute.
ofc.
 
  • #16
meopemuk said:
True, during acceleration I am not an inertial observer. But after I released the accelerator pedal, I move with a constant speed and I may regard myself as an inertial observer, which is boosted with respect to my previous state.

I agree that this is not a perfect analogy for boost, but not a bad one if we disregard the (short) time during which I am stepping on the gas pedal.

Perhaps, a better analogy would be to jump (mentally) to another car that passes nearby.

Eugene.
A reference frame is not an object like a car that has a single trajectory. A boost is not a physical process like acceleration of an object. A boost is a mapping or transformation from one reference frame to another.
 

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