A few questions for physicists

[Daird]

Since the science and tech forum seems to have died, I'll post these here.
1. Could someone explain the hypothesis of time and space being discrete rather than continuous? It just doesn't make sense to me.
2. While you're at it, I recently heard the hypothesis that time is just an artifact of consciousness and doesn't really exist. How does that work when time seems to be part of the underlying fabric of the universe i.e.; no time, no existence?

 

[timtofly]

Time is dependent on light. Light travels through space at a constant speed.

Light currently comes from a very large amount of sources. Time is just the way humans interpret that light, along with the gravitic attraction of the earth to it's major source of light, the sun.

If you look at each photon of light it is discrete. If you look at light through the progression of human history it is linear. So time does not exist. The only thing that exist is how we view the progression of our existence, which we in turn call time.

 

[Gigaz]

Since the science and tech forum seems to have died, I'll post these here.
1. Could someone explain the hypothesis of time and space being discrete rather than continuous? It just doesn't make sense to me.
2. While you're at it, I recently heard the hypothesis that time is just an artifact of consciousness and doesn't really exist. How does that work when time seems to be part of the underlying fabric of the universe i.e.; no time, no existence?

1. There's no real difference between a discrete space where you move from one singular point to the next and a continuous space if the point spacing is sufficiently small. The hypothesis usually comes into play when general relativity demands a singularity with infinity space curvature and density. No length below l_p, no singularity, physics remains valid.

2. You can't really proove that time exists. You know that this moment exists and that you have your brain filled with experiences.
Also, there's nothing special about this moment. Someone could take out your brain, delete the last five minuits, put you where you were five minuits ago and put the brain back in. You totally wouldn't notice. The present is the timestamp of your latest memory.
However, for a proper discussion of this it would be nice to have a proper definition of "time".

 

[Borachio]

Hey, this is all to do with granularity.

Nope. I don't understand it.

http://en.wikipedia.org/wiki/Planck_length

Can someone explain to me about superposition?

 

[illram]

The End of Time caught my eye in the science section of one of my local book stores, but I have not had a chance to read it. From the blurbs and reviews it seems to posit a fundamental rethinking of time within our understanding of physics. Anyone read this book?

 

[BenitoChavez]

1) No idea. I have a degree in physics (somehow) and general relativity and quantum mechanics are a bunch of mumbo jumbo to me.

2) Its kinda like the tree falling in the woods problem. One possible answer is to think of time as a construct made up by humans to define how objects move. For example 1 year is how long it takes for the earth to revolve around the sun. 1 day is how long it takes for the earth to rotate 360 degrees on its axis. Without humans (or any other conscious being) around who would define what a year or day was?

Can someone explain to me about superposition?

Basically an object can exists in multiple states at once, but only when someone isn't measuring it. As soon as someone does, it collapses to a definite state. How they know it exists in multiple states at once if they can't measure it is beyond me though.

 

[Gigaz]

Can someone explain to me about superposition?

Yes, the wikipedia article which you are linking to can do that.

 

[peter grimes]

I read somewhere that Time only makes sense in relation to Entropy, so it's sort of like our experience of time can be thought of as surfing down the entropy gradient.

I won't claim to understand that, though

 

[madviking]

the only problem i have is that i don't think the "magnitude" of time is proportional to the magnitude of the gradient of entropy. the second law of thermodynamics is a marvellous thing but i think entropy and time are just colinear.

but the entropy-as-time theory does bring up an interesting point: if there is zero increase in entropy (i.e. a completely dead universe), is there still time? i tend to think not.

edit: this is a good article on the above.

 

[Gigaz]

the only problem i have is that i don't think the "magnitude" of time is proportional to the magnitude of the gradient of entropy. the second law of thermodynamics is a marvellous thing but i think entropy and time are just colinear.

but the entropy-as-time theory does bring up an interesting point: if there is zero increase in entropy (i.e. a completely dead universe), is there still time? i tend to think not.

edit: this is a good article on the above.

To measure time, you need either something that goes to it's entropy maximum in time or you take a quantum system which is in a superposition of two energy eigenstates. Decaying particles would work, too, but I think that's it.

Let's forget about the actual experimentator and his entropy. I don't think that the measurement itself must cost a minimal amount of entropy.

 

[FredLC]

Basically an object can exists in multiple states at once, but only when someone isn't measuring it. As soon as someone does, it collapses to a definite state. How they know it exists in multiple states at once if they can't measure it is beyond me though.

It all begun with the double slit experiment. When there is no measurement, the flux result shows an interference pattern, even when one particle is thrown at a time. There are three main interpretations to this:

Copenhagen interpretation: the particle is a single one but there is a wave of possible locations for it to be, ans the wave interferes with itself;

Multiple worlds interpretation: All possible paths of the particle exists in a different universe, and in that scale of time and space, the different realities intefere with each other, causing the interference

Feynmen interpretation: as all multiple locations are equally valid prior to measurement, it exists in all possible positions within the same (our) universe;

VERY oversimplified, but the gist of the thesis. There is not other explanation to the interference pattern that I am aware of, and all of them above points to a multiplicity of some sort, because a single item cannot interfere with itself.

All of them also state that the act of measuremente collapses the wave function. This sounds quite mystical, but ins't, really. To see something, you need to illuminate, there is, throw photons at it. In this scale, the photon is sufficiently energetic to alter the path of the illuminated particle. It's kinda like you had to throw an elefant at another to see it run. Probably would disrupt its path.

Regards .

 

[uppi]

Let's forget about the actual experimentator and his entropy. I don't think that the measurement itself must cost a minimal amount of entropy.

There is a minimal amount of entropy required for a measurement: To make a measurement you must erase the state of your measurement device before making that measurement and by the Landauer principle this costs entropy.

 

[Souron]

Since the science and tech forum seems to have died, I'll post these here.
1. Could someone explain the hypothesis of time and space being discrete rather than continuous? It just doesn't make sense to me.

1)Discrete time works like time in any video game, since video games necessarily have a discrete clock. But many games don't make this obvious, since we can only see discreteness when the update cycle is long enough. Discrete time also implies discrete space, at least given our current notions of how time and space are similar. Discreteness means that instead of things moving in a strait line, they follow a grid or mesh, moving "up two, over one" without having a state of being "up one, over one half" in between. Scientific theory proposals that have discrete time and space don't have a strict x-y-z-t grid, so the details of the nature of motion on whatever grid does exist may vary. In established science, time is not considered discrete. Some people will tell you that time is made of discrete units of the plank time, but this is false. Plank time is the smallest measurable unit of time, but that does not imply the former.

2. While you're at it, I recently heard the hypothesis that time is just an artifact of consciousness and doesn't really exist. How does that work when time seems to be part of the underlying fabric of the universe i.e.; no time, no existence?

This is more of a philosophy question. In science, the popular view is that our conscious perceives time the way it does because of how it necessarily works to increase net entropy, while creating an island of order in your head. In philosophy I have no clue who or by what reasoning someone is arguing that such a basic feature of material existence doesn't exist.

 

[Borachio]

From what I've been reading recently, the idea of matter coming in discrete amounts (atoms) didn't catch on very quickly at all. In the late C19th scientists still generally thought that matter was continuous - until the point when there was incontrovertible evidence of its discrete nature. Similar story with light and photons.

Nowadays, it seems, we're going through the same sort of process with the idea of discrete space. And time.

And space isn't a thing, anyway, is it? All there is is a certain relationship between objects. Well, not even objects, at that, but processes.

 

[Gigaz]

And space isn't a thing, anyway, is it? All there is is a certain relationship between objects. Well, not even objects, at that, but processes.

Space is very much a thing. Even without other objects, space can expand and shrink. It can be excited to oscillate. It can even undergo a phase transition (sort of).

 

[Quackers]

So what is physics and why should i care about it?

 

[Borachio]

Space is very much a thing. Even without other objects, space can expand and shrink. It can be excited to oscillate. It can even undergo a phase transition (sort of).

Yes. I mean no.

I know physicists often talk this way. But it's simply not true. Space is not a thing, to the best of my understanding about what it is. And isn't.

When you say "space can be made to expand, shrink, oscillate, and undergo phase changes", just what, exactly, is it that's expanding, shrinking, oscillating and transitioning? And in relation to what does it do this things?

If it's a thing, then it isn't space. If it's a thing then it should be possible to say what it's made of, to isolate a bit of it, to describe its properties and so forth. Which all goes to say that it isn't space.

In the C19th physicists used to talk about the ether, and its properties. Eventually this idea was discredited and for a time people could talk sensibly about space being not a thing. Nowadays we're back with physicists talking about the "matrix", or the "fabric" of space-time, as if it's a thing.

I can see that it's just a way of talking about a difficult concept, but I don't believe physicists do their image any good when they just talk nonsense.

Such... is my opinion.

 

[Gigaz]

Yes. I mean no.

I know physicists often talk this way. But it's simply not true. Space is not a thing, to the best of my understanding about what it is. And isn't.

When you say "space can be made to expand, shrink, oscillate, and undergo phase changes", just what, exactly, is it that's expanding, shrinking, oscillating and transitioning? And in relation to what does it do this things?

If it's a thing, then it isn't space. If it's a thing then it should be possible to say what it's made of, to isolate a bit of it, to describe its properties and so forth. Which all goes to say that it isn't space.

In the C19th physicists used to talk about the ether, and its properties. Eventually this idea was discredited and for a time people could talk sensibly about space being not a thing. Nowadays we're back with physicists talking about the "matrix", or the "fabric" of space-time, as if it's a thing.

I can see that it's just a way of talking about a difficult concept, but I don't believe physicists do their image any good when they just talk nonsense.

Such... is my opinion.

I understand what you mean. You can't remove space, that's why space is not a real thing.
But let's consider the earth. Even without the sun and the stars or any other object we could measure it's rotation. It rotates in relation to space.
The Ether was not discarded because it was problematic from a philosophical point of view, but because of Special Relativity making it unnecessary. And this was before General Relativity was figured out.

 

[Borachio]

I don't think the Earth does rotate in relation to space. It does according to Newtonian absolute space, of course. But I think Einstein, and no doubt someone else before him, debunked the idea of absolute space.

The Earth rotates in relation to other "objects" in the cosmos.

Still, maybe you're right. Maybe it would be possible to detect the Earth's rotation even if it were the only object in the Universe. There's surely a measurable difference in effect between the poles and the equator.

 

[Gigaz]

Still, maybe you're right. Maybe it would be possible to detect the Earth's rotation even if it were the only object in the Universe. There's surely a measurable difference in effect between the poles and the equator.

Oh this has been done long ago.
http://en.wikipedia.org/wiki/Foucault_pendulum