Seattle
Valued Senior Member
I just want to know if "real" is real? What's so real about it? I can't touch it. I can't "keep it real" if "real" isn't real.
Does time exist?
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I just want to know if "real" is real? What's so real about it? I can't touch it. I can't "keep it real" if "real" isn't real.
Do lengths "exist" as multiples of a wavelength ?OK, so we agree change occurs in nature whether or not an observer is present.
Time is our yardstick for measuring change, so that we can relate different change processes, occurring at different rates, in a consistent way). Just as length gives us a yardstick for comparing intervals separating objects spatially, in a consistent way.
Yet, for some reason, nobody ever asks whether length exists.
In a way, it doesn't. It's an abstract concept, invented by human beings to make sense of their world. But it's a footling discussion that interests no one.
Time on the other hand, gets people worked up. It's a bit like magnets in physics: anything invisible is a huge mystery to some people.
Is that how the basic unit of length can be calculated?
I think I have heard of a Planck length...is that the smallest wave length possible or is it just perhaps the smallest observable length?
If the latter ,is there any theoretical limit to how small a length can be?
Are you just asking "Are tomatoes tomatoish?" ?
Have you a definition for "real"? Can you then apply your definition to a particular circumstance?
If you are too general you will not see the trees for the wood
exchemist
Valued Senior Member
Haha, I really hate all this semi-bullshit stuff people love to talk about "Planck length", Planck time" etc. These are rather speculative theoretical concepts for which, as far as I know, no evidence is available.
Be that as it may, as I understand it, "Planck length" is the shortest length at which the laws of physics can be expected to apply. That does not mean that no shorter length is possible, i.e. it does not mean that length itself is quantised, as it were. If that could have any conceivable meaning, which I doubt.
exchemist
Valued Senior Member
Yeah, after all, how real is real? I mean, just how real do you want to be?
It's a bit pointless. I guess length and time, in the abstract, are as real, or not, as a concept such as beauty.
foghorn
Valued Senior Member
Was it on this site that someone showed a clip of Richard Feynman saying ''what does real mean?''
When you touch something it's only modelled as fields interacting with fields, fields are models.
Physics can't prove fields are ''real''. Physics is models.
When you touch something it's only modelled as fields interacting with fields, fields are models.
Physics can't prove fields are ''real''. Physics is models.
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I profoundly disagree with this. If science is about anything at all, it is an attempt to describe the natural world - the "real world" if you insist.
Of course science uses models - language is a model, after all - that does not mean that science is only models. These models do what science attempts to achieve, to describe the real, natural, world.
foghorn
Valued Senior Member
The natural or ''real'' world certainly acts like it is fields, but physics can't prove that it is fields.
So, what's the physics model for measurements? Does physics have a model for how to perform an experiment? Please give an example.
Physics isn't about proof, it's about finding evidence for theoretical 'models' being acceptable explanations.
For instance, what evidence is there that the universe is holographic; that the third spatial dimension we perceive (via measurements, not necessarily accurate) emerges from a background with only two (plus one of time)?
Another example: supersymmetry has no physical evidence to support it; the LHC hasn't delivered on what the theory needs, to be accepted as a reasonable explanation.
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An operator acting on a state vector
The determination of one the possibly many eigenvalues for that operator.
Next question?
exchemist
Valued Senior Member
I don't see these being in conflict. Science models physical reality, doesn't it?
We can never say our models ARE reality: we just hope they get closer and closer to it.
You're saying if I use a metre ruler to measure a distance, it's an operator on a state vector? What state vector?
Which of these possibly many eigenvalues corresponds to a distance of 1 metre? If I divide the distance measured with a ruler, by the distance for the ruler (i.e. 1 metre), what kind of operator is acting?
foghorn
Valued Senior Member
We agree. Physics is about models. What does 'reality' and 'real' mean, is not the realm of physics. Physics is models.
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exchemist
Valued Senior Member
Well, to be accurate, physics is not really about models. Physics is "about" physical reality, but makes models in order to try to represent it.
foghorn
Valued Senior Member
Yes, what else do you think the models are representing ? In the context of my reply to Quarkhead, I said physics can't prove that its model of fields is indeed what 'reality' is.
I may fumble in my explaining.
exchemist
Valued Senior Member
OK agreed.
Yes.
So you don't know what a "state" is? A system can be moving, spinning, sleeping , dancing the fandango or whatever. All at the same time. That is its state. Have you forgotten the defining property of a vector (at least as it's taught at elementary level)?
Try the scalar product operator.
I have a 1 metre ruler which is a standard of distance, or rather the length of the ruler is. The state of the ruler is a consequence of an interaction of a large number of particles. Say the ruler is made of plastic, then I can probably give it some electrostatic charge; the temperature of the ruler can change, But I need to assume I have an ideal element of distance if I want to use it to accurately measure a distance, the measurement will always be approximate, so the best I can do is repeat a measurement enough so I have a statistical result.
If I dance the fandango while holding the ruler, this doesn't alter the ruler's state or that it remains a standard length, more or less. There are more accurate ways of measuring distances including using a laser. But what about the state of the distance measured? What if I want to separate two particles, electrons say, by a distance of exactly 1 metre? Is that possible or do I have to accept an approximate separation?
What does the separation do to the state of each electron or do I take the state of both, and why does it matter if all I want to know is how far apart they are? That is, after considering the accuracy and precision involved (in any measurement). If I alter the distance after determining it, how does the state change as I do this?
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But you aren't conflating a measurement operator in QM with a measurement of distance, using a metre ruler. Hell no.
The state of a pair of electrons (let's assume an entangled state), separated by any distance doesn't usually include the distance. When IBM built its quantum computer the distances between the quantum 'bits' were determined by engineering. Can you say why these distances were chosen, then engineered? Can you say what the distance from here to the sun has to do with QM, or with determining that distance at any time? Or what eigenvalues of quantum states have to do with the length of a ruler?
No?
Lest we forget, the question is what is the state of a distance between two electrons, or between any two things?
Moreover why does the distance correspond to an eigenvalue of a measurement operator? The distance between the ends of a ruler is a quantum state?
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