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bio website edwardfhughes.wordpress.com
location London, UK
age 24
visits member for 3 years, 1 month
seen 3 hours ago

I'm a PhD student at Queen Mary University of London. I work on modern approaches to scattering amplitudes, in particular scattering equations and soft theorems.


Aug
14
comment Do time-invariant Hamiltonians define closed systems?
The point is that having a time-invariant Hamiltonian doesn't guarantee you can describe the dynamics using Poisson brackets! That's why the issue is a little subtle. Quantum systems must have a Hamiltonian and commutation relations by definition, which automatically bypasses such issues.
Aug
14
comment Do time-invariant Hamiltonians define closed systems?
Note that both the sleigh and the rattleback fall into the category of closed systems with non-holonomic constraints. This accounts for the examples in your linked question. There may be other circumstances in which closed systems are non-Hamiltonian, but you'd probably need a dynamical systems expert to answer that question!
Aug
14
comment Do time-invariant Hamiltonians define closed systems?
Excellent question. There's a subtle difference between "having a Hamiltonian" and "being a Hamiltonian system". The latter usually means that you can describe things in terms of Poisson brackets. All the unconstrained closed systems I've ever come across can be described as Hamiltonian systems. I can't find a proof of this however. When you have constraints (specifically non-holonomic ones) then closed systems don't have to be Hamiltonian, as this presentation points out.
Aug
13
comment Do time-invariant Hamiltonians define closed systems?
Hmm - I'm not sure it's quite a duplicate. The OP in this case probably wants some broader physical intuition rather than the mathematics. I think it's worth having both questions to complement each other!
Aug
13
revised Do time-invariant Hamiltonians define closed systems?
deleted 7 characters in body
Aug
13
answered Do time-invariant Hamiltonians define closed systems?
Aug
10
awarded  Popular Question
Jul
25
awarded  Yearling
Jun
16
reviewed Approve How would the laws of nature behave if we reversed time?
Jun
11
answered Counting degrees of freedom in spinor-helicity formalism
Jun
10
reviewed Leave Open Is there a natural (suitable) definition for functional derivative in Curved space time
Jun
10
reviewed Leave Open How much space does an atom occupy?
Jun
4
comment Analogy for the AdS/CFT Correspondence
@Andrew - just a thought about the accuracy of the analogy. Can't you tell the distance between objects by using the fact that there are two images (one on each side of the room)? To do this you'd need to know the size of the room, but this is encoded in the boundary data. This seems like a nice property of the analogy since then boundary data at separated points is encoded by passage through the bulk... It would be interesting to hear people's take on this!
Jun
4
comment What laws are the same in all string theory compactifications?
Agree with @MitchellPorter - this question should be left open. Fine, it's research level, but it isn't too unclear in my opinion. I may answer myself if I get a moment this afternoon!
Jun
4
reviewed Leave Open Why did they used to make the mill chimneys so tall?
Jun
4
reviewed Leave Open What laws are the same in all string theory compactifications?
Jun
4
reviewed Edit Area Integrals when Calculating Force Exerted by Air Pressure
Jun
4
revised Area Integrals when Calculating Force Exerted by Air Pressure
Improved formatting, clarified question
Jun
4
reviewed Edit Horizontal Projection From The Top Of An Inclined Plane
Jun
4
revised Horizontal Projection From The Top Of An Inclined Plane
Improved formatting, made more concise