What is the difference between accelerating and boosting?

My professor claimed in class that there was a difference between an acceleration and a boost. I don't really understand the distinction. If you want to go to a different inertial frame of reference, wouldn't you need to accelerate?

• "If you want to go to a different inertial frame of reference, wouldn't you need to accelerate?" If this were true, studying cosmic rays would be exhausting for sure! Jan 14 '16 at 20:41

Boosting means you are changing a frame of reference; boosting frames doesn't imply any actual motion. When you talk about boosting, you are talking about changing the way you are observing something instantaneously.

Acceleration on the other hand, is a type of motion inside a frame of reference. When you talk about acceleration, you are talking about a particle (or something) changing velocity over time without changing the way you are observing it.

Let's say you are doing a typical SR experiment and you have Alice and Bob flying around in spaceships and such and you have each ship feeding you data. Things outside look one way to Alice and a different way to Bob because of their inertial frames. Let's say they're observing two supernovas and trying to determine their timing relative to each other, and you have all the data you need from the two feeds: apparent distance, redshift from each experimenter's frame of reference, apparent timing etc. You take all Alice's data and all Bob's data and work so Lorenztian mathemagic and you determine that in their center of mass frame, the two supernovas are a certain distance apart and happen one so long after the other, etc...

That's a boost. You used a mathematical adjustment to "see" things in a frame of reference that you can't see. You can do this from your inertial, non-accelerating space station because it's about the data, not the observer.

Then you, Alice and Bob all turn on your rockets and accelerate toward home because its almost time for dinner. You can't do that with a simple mathematical transformation, it requires real energy and physical interactions.

I might use "boost" for a short burst (more like an impulse) and "acceleration" for a more prolonged burst - but both imply a force applied for a certain time in order to effect a change in momentum.

I recommend you ask your professor for clarification. He/she must have had a particular application in mind. In the case of orbital mechanics, the calculations are easier if you "boost" (make a near-instantaneous change in momentum) than if you "accelerate" (accelerate over a sufficiently long time that the orbit changes during the acceleration - which in turn changes the calculations for how the orbit evolves).

• Hmmm I am probably wrong, but I assumed OP's boost is the change of frame of reference used in SR. Thus, when we perform a boost, we multiply a vector times a matrix. If I understood OPs question properly, then the difference is: a boost is s mathematical operation. Jan 14 '16 at 21:01
• If you are right, perhaps the tags on the question need changing... Jan 14 '16 at 21:14