Go Back   Physics Help Forum > College/University Physics Help > General Physics

General Physics General Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old Nov 1st 2014, 07:49 AM   #1
MBW
Senior Member
 
MBW's Avatar
 
Join Date: Apr 2008
Location: Bedford, England
Posts: 668
Past, Which Past?

A recent post on "reversible paths" got me thinking...

As I understand it, most (all?) fundamental interactions in physics are time symmetric.
There is also a fundamental uncertainty / probabilistic nature to all these interactions.
This leads to the (much debated) "many worlds" interpretation of future events.
Turning this around, wouldn't time symmetry then require a similar "many worlds" interpretation of the past?
__________________
You have GOT to Laugh !
MBW is offline   Reply With Quote
Old Nov 1st 2014, 10:50 AM   #2
Forum Admin
 
topsquark's Avatar
 
Join Date: Apr 2008
Location: On the dance floor, baby!
Posts: 2,814
Originally Posted by MBW View Post
A recent post on "reversible paths" got me thinking...

As I understand it, most (all?) fundamental interactions in physics are time symmetric.
There is also a fundamental uncertainty / probabilistic nature to all these interactions.
This leads to the (much debated) "many worlds" interpretation of future events.
Turning this around, wouldn't time symmetry then require a similar "many worlds" interpretation of the past?
I wouldn't say that time reversal leads to Many Worlds, but it is an intriguing idea.

Just for the record, there are 3 main symmetries in QM. P - parity, C - charge conjugation, and T - time reversal. P was considered a sancrosanct until 1956 when the non-conservation was detected in Co decay. This was, to just about everyone, completely unexpected. Later on (I forget what experiments they were) C - violation and CP (both symmetries combined) violation were measured. No one has measured T violation, but it is expected: One of the basic foundations of QFT is that CPT symmetry holds. Thus if CP is violated and CPT is not then we must expect T to be violated.

It would be nice to do an experiment using anti-Co decay, but creating anti-Co is a daunting task. We only recently created anti-Hydrogen.

(According to Classical Mechanics C, P, and T are all good symmetries.)

-Dan
__________________
Do not meddle in the affairs of dragons for you are crunchy and taste good with ketchup.

See the forum rules here.
topsquark is offline   Reply With Quote
Old Nov 1st 2014, 01:19 PM   #3
Physics Team
 
ChipB's Avatar
 
Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,352
To say that all processes are time-reversible is to ignore the 3rd law of thermodynamics. If a drinking glass falls off a table and smashes into a hundred oieces it would take more energy to put the glass back together and back on the table again than the energy liberated when it fell and broke.
ChipB is offline   Reply With Quote
Old Nov 2nd 2014, 04:52 AM   #4
MBW
Senior Member
 
MBW's Avatar
 
Join Date: Apr 2008
Location: Bedford, England
Posts: 668
Many Worlds Test.

Taking my thought a bit further,
If (note big if) the many worlds idea is taken both forward and backward in time,
then looking bakward in time the number of worlds tapers off back to a single event at the big bang,
while looking forward the number of worlds expands seemingly without limit,
(although I supose it could be argued that the eventual "heat death" could be viewed as a single outcome).

However this appears to put a definate skew of one direction against the other (quite closely connected with ChipB's point about Thermodynamics).
This would seem to mandate some kind of T symmetry violation.

One significant argument against the many-worlds interpretation is that it is fundamentally inaccessible to experimental test.
Could Time Symmetry Violation offer some kind of test?
I guess it would be very difficult to define the level of of violation this interpretation would give as opposed to any other competing interpretation.
__________________
You have GOT to Laugh !
MBW is offline   Reply With Quote
Old Nov 2nd 2014, 05:04 AM   #5
MBW
Senior Member
 
MBW's Avatar
 
Join Date: Apr 2008
Location: Bedford, England
Posts: 668
One more thought has just popped into my head.
(Regulars of the forum will know that I sometimes get into an idea popping mood).

I have come across the iterpretation of anti-matter as "normal" matter going backwards in time,
(this was touched apon in Topsquark's post).
One imponderable in current cosmology is the obvious matter anti-matter imbalance in the universe.
Would not a Time Symmetry Violation be just the sort of thing that might explain this?
__________________
You have GOT to Laugh !
MBW is offline   Reply With Quote
Reply

  Physics Help Forum > College/University Physics Help > General Physics

Tags
past



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Help with Past Exam Question on Rolling Disk on Hemisphere physicsninja28 Advanced Mechanics 0 Dec 6th 2015 03:47 PM
Past Paper Question: eigenfunctions for momentum operator zeeshahmad Quantum Physics 0 Apr 29th 2014 10:50 AM
types of welding processes in cswip 3.1 solved papers and past books dhaya Kinematics and Dynamics 1 Dec 10th 2012 03:42 AM
flow past a sphere laephy Thermodynamics and Fluid Mechanics 5 Aug 26th 2009 06:09 AM
past exam question- Urgent C.E Advanced Thermodynamics 3 May 28th 2009 11:16 AM


Facebook Twitter Google+ RSS Feed