Skew-symmetric form Updated +Created
3D rotation group Updated +Created
Particle in a box Updated +Created
Quantum tunnelling Updated +Created
Examples:
Supercomputer by owner Updated +Created
Superfluid helium-4 Updated +Created
Also sometimes called helium II, in contrast to helium I, which is the non-superfluid liquid helium phase.
How to store data in the Bitcoin blockchain Updated +Created
There are apparently two methods:
Specific implementations:
Light cone Updated +Created
The key insights that it gives are:
  • future and past are well defined: every reference frame sees your future in your future cone, and your past in your past cone
    Otherwise causality could be violated, and then things would go really bad, you could tell your past self to tell your past self to tell your past self to do something.
    You can only affect the outcome of events in your future cone, and you can only be affected by events in your past cone. You can't travel fast enough to affect.
    Two spacetime events with such fixed causality are called timelike-separated events.
  • every other event (to right and left, known as spacelike-separated events) can be measured to happen before or after your current spacetime event by different observers.
    But that does not violate causality, because you just can't reach those spacetime points anyways to affect them.
Figure 1.
Animation showing how space-separated events can be observed to happen in different orders by observers in different frames of reference
. Source.
Display manager Updated +Created
Check which you you have:
systemctl status display-manager.service
Tested on Ubuntu 23.10 I see:
● gdm.service - GNOME Display Manager
     Loaded: loaded (/lib/systemd/system/gdm.service; static)
     Active: active (running) since Sun 2023-12-24 10:34:50 GMT; 23min ago
    Process: 1827 ExecStartPre=/usr/share/gdm/generate-config (code=exited, status=0/SUCCESS)
   Main PID: 1850 (gdm3)
      Tasks: 4 (limit: 71817)
     Memory: 6.8M
        CPU: 119ms
     CGroup: /system.slice/gdm.service
             └─1850 /usr/sbin/gdm3
which means I have GNOME Display Manager.
EC2 instance type Updated +Created
Amazon's informtion about their own intances is so bad and non-public that this was created: instances.vantage.sh/
How to teach / Explain why the subject is beautiful Updated +Created
And if you really can't make money from a subject, there is only one other thing people crave: beauty.
Inward Bound by Abraham Pais (1988) Updated +Created
The book unfortunately does not cover the history of quantum mechanics very, the author specifically says that this will not be covered, the focus is more on particles/forces. But there are still some mentions.
Domain name speculation Updated +Created
Dual space Updated +Created
The dual space of a vector space , sometimes denoted , is the vector space of all linear forms over with the obvious addition and scalar multiplication operations defined.
Since a linear form is completely determined by how it acts on a basis, and since for each basis element it is specified by a scalar, at least in finite dimension, the dimension of the dual space is the same as the , and so they are isomorphic because all vector spaces of the same dimension on a given field are isomorphic, and so the dual is quite a boring concept in the context of finite dimension.
One place where duals are different from the non-duals however is when dealing with tensors, because they transform differently than vectors from the base space .
Lie algebra of Updated +Created
We can reach it by taking the rotations in three directions, e.g. a rotation around the z axis:
then we derive and evaluate at 0:
therefore represents the infinitesimal rotation.
Note that the exponential map reverses this and gives a finite rotation around the Z axis back from the infinitesimal generator :
Repeating the same process for the other directions gives:
We have now found 3 linearly independent elements of the Lie algebra, and since has dimension 3, we are done.
Spin half Updated +Created
Domain name registrar Updated +Created

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