The physics of the "present"

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05-18-2012
megafiddle

The physics of the "present"

I don't mean the state of physics in modern times, but the physical nature
of what we call the "present".

Does the "present" have a physical reality outside of conscious perception?
If no one existed to experience time and the present, would the present have
any physical meaning?

It seems to me that without our knowledge or perception of the present, there
would be nothing to determine it. On the other hand, if everyone suddenly
disappeared, it's hard to imagine that it still wouldn't be May 19 2012. But
that would mean that there's something special about May 19 2012. That
with or without us, there is some kind of physical pointer to this point in time.
And I can't imagine the nature of such a pointer.

So possibly time is a continuum, existing all at once, with no physical distinction
between any one point in time and another, as far as one being the "present".
It would only be our perception of that point in time as being "present". And that
would have been the individual perception for each person throughout history.

Or possibly there is no time continuum; there is only the "present", a single "point
in time" which undergoes constant change. We perceive the change as "past,
present and future".

There is of course, the physical quantity of time that shows up in so many physics
equations. The occurance of that term seems independant of "past, present, future"
except for the direction (sign) of the term.

So basically, my question, is there a formal physical definition of "the present"?
05-19-2012
manasij7479

AFAIK, no.
Consider an observer at 'present' looking at earth from 65 million light years away.
Does that mean that the earth still has dinosaurs at 'present'?

It is our consciousness (which itself does not have a definition, I think) that perceives 'present'.
Just as any other coordinate frame, the 'origin', 0 of a time line could be called 'present', but that is easily transformed.
05-19-2012
megafiddle

It does seem that consciousness is involved. Once you remove our own perceptions,
several aspects of time (as we experience it) disappear along with it. The rate and
flow of time is competely subjective, with the rate of our own neural activity as the
reference. The length of a day still has meaning insofar as it is one revolution of the
earth, but there is nothing we can say of it beyond that.

We need a model of time that also explains the conscious perception of time, even
if consciousness itself isn't explained.
There is is one model that I find highly unlikely, the model of a vast number of universes,
each one representing a single step in time. Somehow, things progress through these
individual configurations of matter, and this progression is called time. One big problem
with this is that there would have to be some kind of cosmic temporal pointer that identified
one of these universes as being the present one. It's very hard to imagine how consciousness
could even be possible in such a world of discrete static universes, and even if consciousness
could exist, what is pointing to our "present" state of consciousness?

More likely, I think, is a single universe which undergoes continual change. In such a world it is
always "now". But what differentiates this particular configuration of matter from any others
that preceded it? Or any others that may follow? The configuration of our neurons determine
our perception of "now" as they are part of the material configuration of the universe. It's not
hard to imagine why we are aware of this point in time, as we are a material part of it. But why
aren't people in 1942 also concurrently aware of their present? Or are they?
Just as our "current" configuration of matter exists, so must every previous configuration have
existed, and every future configuration will exist.

Is every conscious being's perception throughout history equally valid then? Is there a "present"
that is only relative?
05-19-2012
grumpy

I disagree that consciousness or perception is involved in the definition of the "present".

I would define the "present" as the total (aggregated) state of existence at the current point in time.

Existence is not the same as observability, observing something is not the same as perceiving it.
05-20-2012
whiteflags

Time is just a human invention with human utility. If we need a model that explains the conscious perception of time, what would we use that model for? We can already objectively measure time. You can measure how much time passed between you and other objects in the universe.

More importantly this may not even be a physics question, I'm thinking it's a psychological or even a philosophical question, depending on the kind of answer you want.
05-20-2012
manasij7479

Quote:

Originally Posted by grumpy

Existence is not the same as observability, observing something is not the same as perceiving it.

That is not correct... as far as my little understanding of Quantum physics and Relativity leads me to believe.
05-21-2012
megafiddle

Quote:

Originally Posted by grumpy

I disagree that consciousness or perception is involved in the definition of the "present".

I didn't mean that consciousness or perception was involved in the physical reality of the "present".

Quote:

Originally Posted by grumpy

Existence is not the same as observability, observing something is not the same as perceiving

it.

I agree, although perception can have high degree of correlation to physical reality. Life would be impossible
or very brief otherwise. I think the question here is, just how correlated is time perception to the physical?

Quote:

Originally Posted by whiteflags

Time is just a human invention with human utility. If we need a model that explains the conscious

perception of time, what would we use that model for? We can already objectively measure time. You can measure how much time

passed between you and other objects in the universe.

More importantly this may not even be a physics question, I'm thinking it's a psychological or even a philosophical question,

depending on the kind of answer you want.

Yes, a model of time perception would be psychological or philosophical.
I would look for a model of time perception so that the perception could possibly be separated from the physical
reality. It is the physical nature I'm interested in.
05-21-2012
Yarin

It's futile at best to try to understand the mechanics of what allows there to be a "past", "present", & "future", I think, considering we exist completely within it & are completely reliant on it.
Of course, one could try to argue with that from a metaphysical PoV, but I don't even know of any such arguments.

But really, "the present" can de defined rather easily, I think, without need for philisophical or scientific rumination.
Simply, it is what is, without consideration of what has been or what will be. This means that the "present" has the same "value" everywhere, always, irrespective even, of the "speed" of time in different places.
Of course though, everyone in the universe has a different observation of the present, and hence differing perceptions of it, but I imagine that's already pretty well understood.
05-21-2012
brewbuck

Given that the laws of physics are symmetrical with respect to time there should be no reason for the past to be any different than the present, but it obviously is. Thermodynamics says that as things change they tend to change into states with more disorder. That can be stated without appealing to any particular time direction. Time appears to have a consistent direction because we originated in a region of the universe with above-average degree of order and are now progressing into less-ordered states (on a medium scale -- on the small scale of humans order can increase noticeably). This is all just due to random fluctuations in entropy throughout the universe. Eventually we'll just be an undifferentiated soup with no clear direction being "forward in time" or "backward in time." Listen to Feynman's very interesting lecture on this topic.

As far as the meaning of "now," that's just a word we made up to describe things that are immediately present in our consciousness, i.e. not memories but actual perceptions of reality. This is not actually a point -- "now" is actually a range of times and events which are all immediately pertinent -- and the radius of "now" depends on who you are, what you are doing, the details of your specific brain, etc.
05-21-2012
phantomotap

I'm presently eating a cookie! ^_^;

Take that naïve perception away and we get to dive into fun theories; would you want your guess to be flavored by physics, philosophy, religion, or how much faster my dog seems to run when he wants nums?

I only ask because you are going to get four very different answers.

Soma
05-21-2012
megafiddle

Quote:

Originally Posted by phantomotap

I'm presently eating a cookie! ^_^;

Take that naïve perception away and we get to dive into fun theories; would you want your guess to be flavored by physics, philosophy,

religion, or how much faster my dog seems to run when he wants nums?

I only ask because you are going to get four very different answers.

Soma

A metaphysical explanation would be very interesting, but it's the objective, purely physical one
that I am wondering about.

One might ask it as, "what time is it if no one is looking?"
And it may just be completely meaningless.

It would seem that certain characteristics of the universe must be there even if no one were around to be
aware of it. There is the problem though of imagining anything about them in the absence of conscious
perception. It's by definition impossible.
The progression rate of time is subjective and variable as we experience it. There is no basis for believing
that time would march on at the same rate that we perceive it, in our absence, whatever that might mean
(there's that problem of imagining it again).
We might not be perceiving the rate of time, but creating it.

Quote:

Originally Posted by brewbuck

Given that the laws of physics are symmetrical with respect to time there should be no reason for the

past to be any different than the present, but it obviously is. Thermodynamics says that as things change they tend to change into

states with more disorder. That can be stated without appealing to any particular time direction. Time appears to have a consistent

direction because we originated in a region of the universe with above-average degree of order and are now progressing into

less-ordered states (on a medium scale -- on the small scale of humans order can increase noticeably). This is all just due to random

fluctuations in entropy throughout the universe. Eventually we'll just be an undifferentiated soup with no clear direction being "forward in

time" or "backward in time." Listen to Feynman's very interesting lecture on this topic.

As far as the meaning of "now," that's just a word we made up to describe things that are immediately present in our consciousness,

i.e. not memories but actual perceptions of reality. This is not actually a point -- "now" is actually a range of times and events which are

all immediately pertinent -- and the radius of "now" depends on who you are, what you are doing, the details of your specific brain,

etc.

We could expand that radius to include our entire lives, and expand the question to one about an era
in the history of the universe instead of just a single instant. Something like the anthropic principle could
explain why the universe happens to be in this era, or what determines the current era. It is simply this
era because we happen to be here in this one to ask about it. There was no one around at other times.

Is there no particular point in time in our absence? are there all points in time in our absence?

Quote:

Originally Posted by Yarin

It's futile at best to try to understand the mechanics of what allows there to be a "past", "present", & "future", I

think, considering we exist completely within it & are completely reliant on it.
Of course, one could try to argue with that from a metaphysical PoV, but I don't even know of any such arguments.

But really, "the present" can de defined rather easily, I think, without need for philisophical or scientific rumination.
Simply, it is what is, without consideration of what has been or what will be. This means that the "present" has the same "value"

everywhere, always, irrespective even, of the "speed" of time in different places.
Of course though, everyone in the universe has a different observation of the present, and hence differing perceptions of it,

but I imagine that's already pretty well understood.

Indeed, we probably know more about physical time than we do about perceived time.

Time would probably be easier to grasp if it were the independant quantity that we perceive it as. But when
it's an inseparable part of the larger space-time, it seems it has a nature that must be different than we perceive.
Just as space is not just an empty void that things float around in.
Our perception of time might be closer to it's physical nature if a 3D model is correct (3 spatial with time separate).
But if the 4D model is correct, with time as one of the 4 dimensions, then I have trouble imagining exactly what it is
we are percieving.
05-22-2012
whiteflags

Quote:

The progression rate of time is subjective and variable as we experience it. There is no basis for believing
that time would march on at the same rate that we perceive it, in our absence, whatever that might mean
(there's that problem of imagining it again).

I disagree with that. I think we need external cues to understand when we think we are, which is what makes our time perception either awful or really accurate. It depends on the stimulus in the environment that we are using: e.g. the ticking of clocks, which is accurate, or just sleeping eight hours and not knowing it. But objectively you have objects moving in the universe, that move even if you aren't paying attention, so they serve as an objective reference. You can measure the amount of movement and the rate of movement for time, just like how the sun moves 15 degrees an hour across the sky. So if you want to be accurate on the passage if time, you should use sources of information that don't depend on subjective observation.

Another good point is that there will be evidence that you exist for a long time (especially if you get fossilized!) so there are ways to objectively affirm that you existed some time between the future after death and the epoch on someone's calendar.

I did manage to find an article that supports what I'm saying, but it's not recent. It could be bunk by now.
05-22-2012
megafiddle

Quote:

Originally Posted by whiteflags

I disagree with that. I think we need external cues to understand when we think we are, which is what makes our time perception either awful or really accurate. It depends on the stimulus in the environment that we are using: e.g. the ticking of clocks, which is accurate, or just sleeping eight hours and not knowing it. But objectively you have objects moving in the universe, that move even if you aren't paying attention, so they serve as an objective reference. You can measure the amount of movement and the rate of movement for time, just like how the sun moves 15 degrees an hour across the sky. So if you want to be accurate on the passage if time, you should use sources of information that don't depend on subjective observation.

Another good point is that there will be evidence that you exist for a long time (especially if you get fossilized!) so there are ways to objectively affirm that you existed some time between the future after death and the epoch on someone's calendar.

I did manage to find an article that supports what I'm saying, but it's not recent. It could be bunk by now.

I don't completely disagree with that.
Any number of things can serve as a clock, including our own
mental processes. And some can use their "internal clocks" pretty
accurately. In that sense you could say that we perceive time with
some degree of objectivity.

But a feeling of time flow is only that - a feeling or perception. How
do you know which of the various perceptions we have are the "real"
or "correct" ones? Which reflect the "real" flow rate of time?
I could argue that the sense of flow that we have when unconscious
is most accurate since conscious perception is absent for that interval.

When we try to imagine time in our absence we are usually making
two mistakes. First if are imagining anything at all we are not absent.
And second, it is only a model we are imagining. We are still separated
from the physical world by the interface of our senses.

True, whatever time is doing now, it will continue to do after we are gone.
Also true, we, and our internal clocks are real enough. But we shouldn't
mistake the model for the real thing. When we are gone, certain things
about time, as we perceive it, will be gone also.
05-30-2012
MK27

:D What multi-disciplinary madness have I been missing?!??

Quote:

Originally Posted by Newtonian curmudgeon

I would define the "present" as the total (aggregated) state of existence at the current point in time.

Existence is not the same as observability, observing something is not the same as perceiving it.

I agree that the "existence of everything" is not observability, but it also does not define the present any more than a warehouse defines a box on a shelf. You need a point in space (the existence of something more specific) for your definition of present, since the "totality of everything" at a fixed point in time is a) abstract at best; b) mostly irrelevent since the speed of light localizes things.

So, here's your answer:

Matter is existence, existence is matter. Time is fundamental to atomic matter, but while our physics is entirely about atomic matter, I have never seen it asserted that matter is/could not be anything but atomic (in fact I think the early points in big bang theory imply very strongly that existence/matter is the foundation for atomic physics, but cannot quite be synonymous with it, there is a point in time before atomicity). So while time is a fundamental aspect of atomic matter, it perhaps is not a fundamental aspect of "matter", which is why it does not make sense to speak of the beginning or end of existence (the same way "literally nothing" is a paradoxical concept), only the beginning and end of our universe.

The same is probably true of space (it is no more fundamental to matter than time), which makes "what is matter, beyond the atomic?" kind of an interesting question. However, I think it is fundamental to physical science that the question cannot be addressed (or, can't be addressed yet); no one asks what are the smallest sub-atomic particles "made of"; there is only one possible answer (matter) which makes it circular (it's the same question as "what is matter made of"). Or you say "quants of force", which refers to matter's relationship with itself (matter as the medium of energy). Matter is existence, existence is matter.

The mind is a state machine that creates the holographic world of our perceptions. Like any electronic device the brain clearly involves specific frequencies (time cycles) -- we do not percieve things with infinite granularity, time-wise, which is why the color red is fully present to you instead of being some pulse. The fact that the speed of light is a constant for atomic matter is not arbitrary; we can consider frequencies as "steady" and that is what makes heterogenity in the form of matter meaningful to us and the tiny particles of which we are made. Without that fundamental measuring stick for precise and equal units, there would not be eg, the equality of two protons. 'c' is the bounds of the form of our universe (it deliniates and defines the beginning and end of it).

Which takes us to the answer: the present is not a "point" in time, it is a duration, but it is not something we experience as a duration; it involves phenomenon that do have a beginning and an end and can be considered in greater granularity in atomic physics, but for our perception, these phenomenon are effectively simultaneous -- their beginning and end are always present to us. I'd assume this duration is on the order of milliseconds, like sound. A high pitch and a low pitch are different but they are the same in the sense that they are both singular and present all at once, although we can infer the way they take place in time via the concept of frequency. Another example: gamers may bicker about the experiential significance of 80 fps vs. 20 fps, but no natural human being will ever bicker about the experiential significance of 1000 fps vs. 1000000 fps (unless it is with reference to the perception of heat, lol).

People have written here about the mind in relation to clocks, which is good (atomic matter is also a clock, think of c again). Now consider that a second hand has a width.

The "duration of the present" is given to us within a correlative region of space, which is why the mind experiences space as defined by components such as shape, sound, color, etc. It's the fundamental frequency of your state machine, the carrier wave of the mind. You're atomic, inside and out.

Everyone understand now? ;) There is a joke in here about the "Hertz donut" but you really have to be there for that...
05-30-2012
manasij7479

Quote:

I have never seen it asserted that matter is/could not be anything but atomic

Maybe I'm missing your point, but matter is quite commonly considered as waves, in duality with particles.

Quote:

The "duration of the present" is given to us within a correlative region of space, which is why the mind experiences space as defined by components such as shape, sound, color, etc. It's the fundamental frequency of your state machine, the carrier wave of the mind. You're atomic, inside and out.

How does that fit in with the time-energy uncertainty ?
05-30-2012
brewbuck

Quote:

Originally Posted by manasij7479

Maybe I'm missing your point, but matter is quite commonly considered as waves, in duality with particles.

Matter behaves in ways that can be predicted using equations that involve waves. This just means it can be predicted like that, it doesn't mean that particles are waves. Whether a particle "is" a wave is maybe not even a meaningful question.

The wave function of any particle is, in general, complex-valued and thus has no direct physical meaning. What the wave is "waving" is measured in units of probability amplitude, it is not a real thing which exists. It is just a mechanism to predict what happens.
05-30-2012
manasij7479

Quote:

Originally Posted by brewbuck

Matter behaves in ways that can be predicted using equations that involve waves. This just means it can be predicted like that, it doesn't mean that particles are waves. Whether a particle "is" a wave is maybe not even a meaningful question.

Similarly, "Matter behaves in ways that can be predicted using equations that involve" particles.
I didn't say that a particle is a wave, but 'matter' and 'particle' are definitely not the same thing, afaik.

Quote:

The wave function of any particle is, in general, complex-valued and thus has no direct physical meaning. What the wave is "waving" is measured in units of probability amplitude, it is not a real thing which exists. It is just a mechanism to predict what happens.

Everything in physics is a mechanism to predict what happens, or abstractions of what is happening; physical significances are totally a human invention.
The probability function wave does not predict the probability of a 'particle' existing at a point in space but the magnitude of the behaviour exerted , for example chemistry uses this to determine interaction between atoms quite effectively.

N.B: This just my understanding of how things are, and I'd be happy if you point out where I'm wrong.
05-30-2012
brewbuck

Quote:

Originally Posted by manasij7479

Everything in physics is a mechanism to predict what happens, or abstractions of what is happening; physical significances are totally a human invention.
The probability function wave does not predict the probability of a 'particle' existing at a point in space but the magnitude of the behaviour exerted , for example chemistry uses this to determine interaction between atoms quite effectively.

If you are saying that the wavefunction is a statistical property of a whole ensemble of particles, that isn't the case -- it works even for a single particle, and really does denote probability, not collective tendencies. But wave/particle dualities occur in many contexts and not all of these are the same. The equations are similar because many physical relationships can be described as proportionalities between some quantity and its various derivatives. Mathematically, those sorts of systems have wave-like solutions. But the fact that waves arise everywhere doesn't signify that they are all of the same nature.

I base my own interpretation strongly on Feynman's, and by no means claim that it is the only valid one.
05-31-2012
phantomotap

This link will take you to a video that is not safe for work!

^_^;

I finally dug up the link.

I was going to post this the other day.

This is "off topic", but I immediately thought of this when reading one of the posts.

Soma

"Dimension X" NINJA TURTLES/10th DIMENSION RAP by Lil Deuce Deuce - YouTube
05-31-2012
megafiddle

The wave nature of particles (e.g. electrons) can be seen in the double slit experiment.
Electrons will produce interference patterns, much like light. These interference patterns
of alternating light and dark bands are characteristic of waves.
In addition, there is a probability wave function which predicts where the electrons will
strike the target and therefore where the bands will appear.
05-31-2012
brewbuck

Quote:

Originally Posted by megafiddle

The wave nature of particles (e.g. electrons) can be seen in the double slit experiment.
Electrons will produce interference patterns, much like light. These interference patterns
of alternating light and dark bands are characteristic of waves. In addition, there is a probability wave function which predicts where the electrons will
strike the target and therefore where the bands will appear.

It's not "in addition," it's the whole reason it happens. The wavefunction is not the electron. For just one particle you might convince yourself that the wavefunction is the electron, but for more than one particle it all breaks down. For instance, a system of two electrons has ONE wavefunction. You cannot write this wavefunction in terms of the sum of two wavefunctions belonging to each electron individually, it doesn't come out right. electron != wave
05-31-2012
megafiddle

Quote:

Originally Posted by brewbuck

It's not "in addition," it's the whole reason it happens. The wavefunction is not the electron. For just one particle you might convince yourself that the wavefunction is the electron, but for more than one particle it all breaks down. For instance, a system of two electrons has ONE wavefunction. You cannot write this wavefunction in terms of the sum of two wavefunctions belonging to each electron individually, it doesn't come out right. electron != wave

I didn't mean that the wave function was the electron. I would say that the wave function
describes the electron, in this case it describes it's location. However the electron does
behave as if it were a wave; cover one slit and the interference pattern disappears.
Isn't that what is meant by the "wave nature" of a particle?
05-31-2012
manasij7479

Quote:

Originally Posted by megafiddle

I didn't mean that the wave function was the electron. I would say that the wave function
describes the electron, in this case it describes it's location. However the electron does
behave as if it were a wave; cover one slit and the interference pattern disappears.
Isn't that what is meant by the "wave nature" of a particle?

You are confusing de Brouglie waves with probabillity waves .
05-31-2012
brewbuck

Quote:

Originally Posted by megafiddle

I didn't mean that the wave function was the electron. I would say that the wave function
describes the electron, in this case it describes it's location. However the electron does
behave as if it were a wave; cover one slit and the interference pattern disappears.
Isn't that what is meant by the "wave nature" of a particle?

When you cover one slit the interference disappears because the wave function isn't interfering anymore, it still doesn't mean the electron is a wave. This is in contradiction to what you read in introductory quantum texts, but not contradictory with what you read in the more advanced texts. It becomes clearer when you start considering systems of more than one particle.

There is a great lecture by Feynman which was videotaped, and it's on Youtube. He addresses this exact question at the end of the lecture. When I get home I can post a link. For now, it basically goes like this (paraphrased):

Student: "You just spent all this time telling me that things are particle, but then you show me all these equations that look like the equations of waves. So, aren't you just being sneaky and trying to hide the fact that your theory of matter is really just a wave theory?"

Feynman: "It's true that for a single particle the equations are wave equations. A wave is a function of position and time. But things change when you consider systems of more than one particle. There is a wavefunction for the system, and it is a function of multiple positions and time. That is not a wave. Further, if a single wavefunction describes more than one particle, how can it be said that this wavefunction represents this particle or that particle? You can't."
05-31-2012
megafiddle

Quote:

Originally Posted by manasij7479

You are confusing de Brouglie waves with probabillity waves .

Yes, it is de Broglie waves that I'm thinking about. Doesn't that apply to the wave nature of electrons
and the interference patterns in this case (the double slit experiment)?

Quote:

Originally Posted by brewbuck

When you cover one slit the interference disappears because the wave function isn't interfering anymore, it still doesn't mean the electron is a wave. This is in contradiction to what you read in introductory quantum texts, but not contradictory with what you read in the more advanced texts. It becomes clearer when you start considering systems of more than one particle.

There is a great lecture by Feynman which was videotaped, and it's on Youtube. He addresses this exact question at the end of the lecture. When I get home I can post a link. For now, it basically goes like this (paraphrased):

Student: "You just spent all this time telling me that things are particle, but then you show me all these equations that look like the equations of waves. So, aren't you just being sneaky and trying to hide the fact that your theory of matter is really just a wave theory?"

Feynman: "It's true that for a single particle the equations are wave equations. A wave is a function of position and time. But things change when you consider systems of more than one particle. There is a wavefunction for the system, and it is a function of multiple positions and time. That is not a wave. Further, if a single wavefunction describes more than one particle, how can it be said that this wavefunction represents this particle or that particle? You can't."

Don't you get the same results though, whether there are many electrons or just one? When the beam intensity
was reduced to the point where only a single electron at a time was passing through one of the slits, the interference
pattern persisted. Same as a dense beam.

Feynman's lectures were great, I've watched all that I could find. He has a way of explaining a most
difficult subject.
05-31-2012
brewbuck

Quote:

Originally Posted by megafiddle

Don't you get the same results though, whether there are many electrons or just one? When the beam intensity
was reduced to the point where only a single electron at a time was passing through one of the slits, the interference
pattern persisted. Same as a dense beam.

With many electrons the pattern builds up quicker, but other than that it's not different than a single electron. The electrons in the beam for the most part do not interact with each other and so they can be described by independent wavefunctions. In other circumstances (like the two-electrons-in-a-box problem) there is an interaction and therefore only a single wavefunction for the system.

"Real waves" can interfere with other waves. Wavefunctions are not like that, they can only interfere with themselves.

I'm not arguing at all that something wave-like is happening, I just refuse to identify "electron" with "wave," a la Feynman. This isn't a settled issue! ;)
05-31-2012
brewbuck

Here's the video I was thinking of:

Feynman on Wave Particle Duality (QED Lecture in New Zealand) - YouTube

You've probably already watched it if you've watched/listened to Feynman, but I toss it out there just in case.
05-31-2012
megafiddle

Quote:

Originally Posted by brewbuck

With many electrons the pattern builds up quicker, but other than that it's not different than a single electron. The electrons in the beam for the most part do not interact with each other and so they can be described by independent wavefunctions. In other circumstances (like the two-electrons-in-a-box problem) there is an interaction and therefore only a single wavefunction for the system.

"Real waves" can interfere with other waves. Wavefunctions are not like that, they can only interfere with themselves.

I'm not arguing at all that something wave-like is happening, I just refuse to identify "electron" with "wave," a la Feynman. This isn't a settled issue! ;)

In the case of electrons then, the wave function of a single electron is interfering with the same wave function through the other slot?
As opposed to electromagnetic waves, for example?
05-31-2012
megafiddle

Quote:

Originally Posted by brewbuck

Here's the video I was thinking of:

Feynman on Wave Particle Duality (QED Lecture in New Zealand) - YouTube

You've probably already watched it if you've watched/listened to Feynman, but I toss it out there just in case.

Thanks for the link. I had seen it before, but it makes somewhat more sense now.

So for a single particle, the probability wave function is mathematically the same as the the amplitude wave function for an electromagnetic wave?
05-31-2012
brewbuck

Quote:

Originally Posted by megafiddle

Thanks for the link. I had seen it before, but it makes somewhat more sense now.

So for a single particle, the probability wave function is mathematically the same as the the amplitude wave function for an electromagnetic wave?

Yes, which is why the wave theory of light works so well.
06-01-2012
MK27

Quote:

Originally Posted by manasij7479

Quote:

Originally Posted by mk27

I have never seen it asserted that matter is/could not be anything but atomic

Maybe I'm missing your point, but matter is quite commonly considered as waves, in duality with particles.

My point was that it's atomic matter that is considered as waves and particles ("quants of force, which refers to matter's relationship with itself (matter as the medium of energy)"); my understanding of big bang theory is that this is only true after a certian point in time, but that the existence of the mass (ie, matter/energy) of the universe preceeds the atomic state which we understand in terms of waves and particles.

I did not google this because I assume someone here will put me to rights anyway, but I have it my head that there is considered to be a relationship between the value of 'c' and the (equally constant) amount of mass/energy (matter) in our universe. Atomicity is about the unit, ie, the possibility of there being multiples of one; this is I think also the basis of logic (the potential equivalence of two or more things, mental/conceptual or physical/real)*. But that does not apply to the (mental concept of) "matter"; we refer to matter in various forms but not various "matters" plural; although the meaningfulness of that may be a semantic illusion. I've equated matter with existence because it seems they are actually semantic equivalents. That means using the term matter in a more inclusive way than traditional physics, because eg, a photon particle is not considered a form of (atomic) matter, it's a form of (atomic) energy. But notice while it might be meaningful to refer to matter independent of energy, I am dubious about referring to energy independent of matter. Again, it seems that matter is a medium for energy / energy is a conceptual way of understanding matter (hence, it is not more matter, it is about relationships involving matter, so we say: energy is not matter, matter is not energy, but the two are intrinsicly intertwinned).

To my mind the idea that "existence" is just a semantic illusion seems logically implausible; but (logically) I don't see how it can be considered as anything other than matter (the inclusive "matter/energy" definition), which seems purely logical in nature (hence, the characteristics of the atomic form).

* there was a page I found in a GD thread a while back that involved a sort of semantic map of wikipedia, by way of which you could see how any given article related to another in a branching (historical/time axis) tree. A few people remarked how virtually everything was descended from math, but in fact, this was because almost everything required the concept of number and there are a few notable exceptions such as reason.
06-02-2012
MK27

I think that was pretty clear, maybe using something like "currently recognizable quantum mechanical matter" might have been a better term than atomic.

The point in the big bang I am referring to is between the "Plank epoch" and the "Grand unification epoch" here:

Chronology of the universe - Wikipedia, the free encyclopedia

It's mentioned that these points are very speculative and our current knowledge of them permits a wide range of theories, eg, I think "brane inflation" must be a superstring/multiverse model. Point being that some of the fundamental laws of physics in our universe that we take to reflect immutable characteristics of what we recognize as quantum mechanical matter may not be fundamental characteristics of matter (or "what matter is made of") but more arbitrary, relecting the state of this "ultimate" matter under certain (arbitrary) conditions or as a consequence of certain (arbitrary) events.

The reason I find that philosophically interesting is it isolates existence as a more fundamental property of "matter" than anything else; "it" may (perhaps: logically must) exist outside the form which defines space time to us. So the "reason" for existence is because existence is a property of what is (matter, in a broad sense). Sort of circular, but I like it because it means investigations/questions about "existence" are questions about the nature of matter, sans metaphysics and misapplications of space-time based cosmology (which lead to non-sensical problems such as "What was there before there was anything?" -- nothing, ha-ha, but I think a more realistic answer is there is/was no such time period).

Matter is existence, existence is matter. I should start a cult. We could sell little Steven Hawking icons and "GOD HATES METAPHYSICS" buttons :cool:.