# Observers

Discussion in 'Physics & Math' started by arfa brane, Apr 18, 2017.

1. ### QuarkHeadRemedial Math StudentValued Senior Member

Messages:
1,579
OK. So your assertion is that an observed system behaves in exactly the same way as an unobserved system?

Or to put it another way; if I determine the eigenstate of a system to have particular value at a particular time, I may assume this system always to have had that particular value in the past and always will.

3. ### exchemistValued Senior Member

Messages:
7,972
No that's silly. He's talking about a light switch, not every physical system in the universe.

5. ### Confused2Registered Senior Member

Messages:
513
Clocks seem to carry on just the same whether or not they are observed.

7. ### gmilamValued Senior Member

Messages:
3,074
How would you know the state of an unobserved system without... (wait for it...) observing it?

8. ### QuarkHeadRemedial Math StudentValued Senior Member

Messages:
1,579
No he is using an everyday analogy to give a "proof" of the general case
Take a peek at this....
ipso facto I rest my case

9. ### Confused2Registered Senior Member

Messages:
513
exchemist likes this.
10. ### DaveC426913Valued Senior Member

Messages:
11,422
No. The initial assertion was:
Nature goes on with or without observations.
To which you responded: How can you be sure? Do you have a proof of this bold assertion?

I am simply pointing out that nature did go on while it while not being observed - as witnessed by the fact that, (under normal circumstances) everything was where it was expected to be* when it was subsequently observed.

It is an inescapable conclusion that, whatever reality existed in that room before I left was preserved (perhaps recorded and replayed, but still - preserved). i.e. "nature" - as I experienced it - did indeed "go on" without being observed.

* stuff may move, but it's not unexpected

It's possible to extrapolate to "an observed system behaves in exactly the same way as an unobserved system", but I'd have to think about that.

11. ### DinosaurRational SkepticValued Senior Member

Messages:
4,884
The significance of a human observer has been exaggerated due to technical writers misunderstanding explanations provided by knowledgeable physicists

The Copenhagen interpretation of quantum reality makes a remark similar to the following

12. ### QuarkHeadRemedial Math StudentValued Senior Member

Messages:
1,579
Oh dear - what does it mean for "nature to go on"?

Yes you would. A quantum state (for example) remains indeterminate until measured.

13. ### DaveC426913Valued Senior Member

Messages:
11,422
Agree. It's not exactly a scientific term, but I didn't choose it.

Nonetheless, I can leverage that ambiguity. Essentially, in this context, I am determining it to mean anything I, as a human mortal, can detect. i.e. I know that what I experience as the natural world is preserved while I am not watching.

This is really a sidebar; it is not really germaine to the primary thread, I was just responding to the challenge of whether nature ticks along when we're not watching.

14. ### arfa branecall me arfValued Senior Member

Messages:
6,217
With which event?

An event looks a lot like an interaction/observation, at least in SR it does. Events convey information too.

Note how a spacetime event is effectively a measurement of time and distance.
Note also how difficult it is to show that a measurement can be of anything else than time and distance.

15. ### DaveC426913Valued Senior Member

Messages:
11,422
Colour? Mass? Charge?

16. ### arfa branecall me arfValued Senior Member

Messages:
6,217
I'm sorry Dave, you can't measure that either.

How do you measure mass, here on planet Earth? You weight it: you get information about a displacement, calibrated to standard kg, i.e. you actually measure a distance.
A balance scale lets you calibrate the weightings, at zero displacement two different masses are equally weighted.

See if you can do it another way.

17. ### The GodValued Senior Member

Messages:
3,546
I said I do not have the proof, mainly because the issue of observation classically and QMly may be different.

Now take two modus of observations..

1. Monitoring the system by measuring the light signal transmitted/emitted by the observed system.

2. Monitoring the system by sending the light signal from observation device and recording thereof.

I feel, that methodology 1, will fall into a description where observation may not impact the system state. But in #2 it could.

18. ### arfa branecall me arfValued Senior Member

Messages:
6,217
Two years ago, the first experiment that verified the quantum Zeno effect applies to 'real' space measurements of atomic motion was performed at Cornell.

--https://en.wikipedia.org/wiki/Quantum_Zeno_effect

Clearly measurement has a time component--wavefunctions don't "collapse" instantaneously.

19. ### The GodValued Senior Member

Messages:
3,546
Ex1. Take for example BH BH merger (GW fame), the event had nothing to do with our observation / detection.

Ex2. Take any Supernova observation, no interaction with event whatsoever, it is the radiation emitted which we measure/observe. We cannot even send a probe light signal.

So the interaction is basically with the (light, sound, spacetime changes) only in case of measurement, not with the event as such.

20. ### arfa branecall me arfValued Senior Member

Messages:
6,217
'sigh'
Then how do we know such things happen? How do we explain the gravitational wave observatory and its observations?
Yes, we interact with the radiation emitted, this in fact is the "supernova event", which we can say absolutely nothing about until the light arrives.
What you seem to be saying is we can't interact with such an event if we aren't "there when it happens". But we do interact with it at a different time.

21. ### The GodValued Senior Member

Messages:
3,546
We observed merging of BHs without any EM radiation of that event.

We observe someone honking without EM radiation. (Sound waves).

Detecting the EM radiation as emitted by an object (event) or detecting a sound wave as emitted by a trumpet, is not same as interacting with the event.

You have this habit of convenient improvisation without acknowledging. Take care.

22. ### arfa branecall me arfValued Senior Member

Messages:
6,217
Incorrect. We did not directly observe gravitational waves, we observed two laser beams interacting with mirrors and detectors.

Detection is an event, you twit.

23. ### The GodValued Senior Member

Messages:
3,546
Good for you kid, you are learning lot of things; Physics, maths and abuses too.

But I suggest go slow on abuses, and don't even try to teach your pop how to screw.

Last edited: May 6, 2017
danshawen likes this.