Time - continuous or quanta?

[dogjones]

I was just wondering whether time is a sort of Heraclitian 'continuous flux' or whether it's quantised into distinct units. I realise these may be the wrong terms to use. Basically, is there a generally accepted physical view of time which deals with this old distinction?

 

[yairhol]

I would say that time is continuous but for practical matters it is as quantized as your most accurate clock.

Regards,
Yair

 

[drkitten]

I was just wondering whether time is a sort of Heraclitian 'continuous flux' or whether it's quantised into distinct units. I realise these may be the wrong terms to use. Basically, is there a generally accepted physical view of time which deals with this old distinction?

My understanding is that you can get some very very esoteric discussions going among the more theoretical sort of physicist by asking this question -- especially if you're buying.

Among the more practical sort (i.e. those who are aware of measurement errors), you're likely to get a shrug and an offer to pick up the next round.

If you actually want answers, the theology department is down the hall. They may not be correct, but at least they're certain.

 

[fls]

Last time I discussed this with a physics PhD student, he said "quanta", because of the symmetry of time and space. The geometry of space requires quantization because of self-similarity (I don't remember if this was a necessary feature, although it would be nice if it was) and some features of the geometry are quantized, such as winding numbers. But (as you can tell from the reference to winding numbers) he was on the string theory bandwagon, so I don't know if this was an answer specific just to that approach to the geometry. And I don't know if these were necessary, or just possible features (my impression from other sources was that configurations where winding numbers were relevant were just one of many possible configurations). And, without remembering the details, I read somewhere that there are features that time and space do not share, anyway.

My hope is that a real physicist will enter this thread and explain what I really meant to say.

Linda

 

[Hellbound]

This is something I've wondered, too.

I've heard various references to the Planc Time as being the unit of quantized time, for example. Supposedly, anything happening with an interval less than this can't be seperated as to the order or occurence. Of course, I haven't looked in-depth on this yet, and it's highly possible, nay, even probable that I'm mis-remembering something (heck, I may not have even membered it properly the first time!).

fls:

As to time and space, they do have different features, but those features sets apparently "swap out" in certain conditions (such as large gravity fields). So space can become timelike and time spacelike, at least according to current theory. Again, though, I'm no expert...just an interested layman

 

[Ivor the Engineer]

My hope is that a real physicist will enter this thread and explain what I really meant to say.

Linda

I think you mean a theoretical physicist. A real one won't know the answer, (s)he'll just want to do an experiment to get more data

My guess: Quantized.

(Well that's what my VHDL simulator says anyway)

 

[Jimbo07]

(Well that's what my VHDL simulator says anyway)

Nice.

I've wondered, if quantized time turns out to be true, whether we can use an analogy to digital logic... but this does get back to my Beginnings thread (Here). Is there any benefit for us, as interested lay people, to sitting around speculating on a forum? Shouldn't we just give each other some links and topics to research (such as Loop Quantum Gravity, IIRC)?

 

[fls]

Is there any benefit for us, as interested lay people, to sitting around speculating on a forum? Shouldn't we just give each other some links and topics to research (such as Loop Quantum Gravity, IIRC)?

The problem for me is that what I'm looking for isn't explained in the books written for lay people, but reading through papers written for physicists is too tough. So if you've got some links, bring 'em on.

Linda

 

[Jimbo07]

I first stumbled across Loop Quantum Gravity in Scientific American. I find that to be a decent bridge between reputable journals and comic books!

Honestly, for the little physics I know, once I wanted to step beyond SciAm, I had to go to textbooks (and available professors and... you know... a university education ). Getting any 'real' knowledge of physics is not a trivial endeavour, even if you work problems on your own. Heck! I sure don't know much. I have almost zero formal training in Cosmology (that's why many of my questions seem to relate to it).

fls: please comment in my other thread. It would be great to get more ideas on the subject!

 

[illogical]

there's a difference between the QFT guys and the relativists. for instance, string theory is background dependent. at least that is what Smolin claims.

there are some papers in the arxiv that use chronons. i suspect that quantizing something besides matter/energy will solve some of the problems. *if* the universe was a computer program, that would explain both quantum mechanics, time, and more.

 

[illogical]

Is there any benefit for us, as interested lay people, to sitting around speculating on a forum?

the theorists and phenomenologists need more data! without experiments, none of these issues will be solved. "speculating" is exactly what the loopys and stringies are doing.

 

[TheDon]

Time equals distance divided by speed, right? So the shortest time that is measurable would be the shortest distance divided by the fastest speed. As I understand it, the shortest distance it is possible to measure in any way whatsoever is the Planck distance (something x 10^-34 metres), and the fastest speed is 3x10^8 m/s, that of light in a vacuum. So the smallest time unit is the first (very small) number divided by the second (very big) number, to give you a very small fraction of a second.

Or is it that the wrong way round?

 

[Yllanes]

First of all, of course discrete space <=> discrete time, because as we know the real important concept is that of spacetime.

This issue has come up several times, you can search this subforum for some discussions. The summary is that in General Relativity spacetime is continuous, but a quantised spacetime seems to be a model independent feature of all our ideas for quantum gravity (it's in string theory, in LQG and in other models). Of course, all of these ideas are still very hypothetical, but everyone seems quite confident the eventual theory for quantum gravitation will have a discrete spacetime. Here is a (technical) review. I think at least the first section, which gives some heuristic arguments in favour of a discrete spacetime, can be followed without too much background.

 

[SomeGuy]

Don't you guys realize that if time is quanta's that would give an absolute upper limit to the speed of computer processors...!

This is horrible!!

 

[Cuddles]

Bascially, we're fairly sure it's quantised, but the energies required to test it are so much higher than we can reach that it might not ever be possible for us to actually know for sure.

I think you mean a theoretical physicist. A real one won't know the answer, (s)he'll just want to do an experiment to get more data

Hmm, are you psychic by any chance?

 

[Ivor the Engineer]

Hmm, are you psychic by any chance?

Nah, I just work with a few.

 

[dogjones]

Time equals distance divided by speed, right? So the shortest time that is measurable would be the shortest distance divided by the fastest speed. As I understand it, the shortest distance it is possible to measure in any way whatsoever is the Planck distance (something x 10^-34 metres), and the fastest speed is 3x10^8 m/s, that of light in a vacuum. So the smallest time unit is the first (very small) number divided by the second (very big) number, to give you a very small fraction of a second.

Or is it that the wrong way round?

Does 'measurable' = 'in existence'?

 

[Hellbound]

Does 'measurable' = 'in existence'?

In this sense, pretty much. It's comparable to the limitations that create, for example, Hiesenberg's Uncertainty Principle (spl?). At least, according to our current theories...there's always the possibiity for something new to come along.

Essentially, this is what I was remembering before. Even if there was something that happened in a shorter time than this, or a smaller distance, there's no way to seperate the two events and determine if one happened before or after the other, or if they occurred in the same place or not (speaking of the distance). And if it's not measurable, then that means it has no observable physical effect, whether we're there to measure it or not.

 

[dogjones]

Point taken Huntsman, although I guess this sidesteps the distinction. If there is no way to separate events in a shorter time than this than whether time's continuous or quantized is irrelevant (and possibly unknowable)?

On a totally separate note, I read the second half of your sig and immediately thought of a line from Ursula LeGuin's A Wizard of Earthsea:

"...And the truth is that as a man's real power grows and his knowledge widens, ever the way he can follow grows narrower: until at last he chooses nothing, but does only and wholly what he must do..."

 

[Hellbound]

I've read some short stories based in that scenario, but don't think I've read any of the novels. Might have to look for a few

And what I stated was only as we currently understand. There's always a possibility that we're wrong It's similar to considering the Hidden Variables hypothesis for quantum entanglement...if it's true it'd have to be because of something even wierder than the wierdness we already have. And, or coursee I may be way off (again, I am not na expert, just an interested and well-read layman).

And that possibly unknowable hits it on the head. It's like the HUP: You can't determine momentum and location precisely, and the more precise you measure one, the less precise the other. This is due to physical limitations: we can only measure it by bouncing something off it. Likewise, it can only interact by contacting something. So, we can bounce a particle off it (such as a photon or graviton). But, the more precise we want to measure the position, the smaller-wavelength particle we have to use, which means higher energy which means momentum gets whonked out. And vice-verse, we use lower-energy to measure momentum of the particle, but that smears out it's location. And this holds true for natural processes, as well, as something has to interact with a particle for anything to happen.

It's the same concept with the time idea. Since there is a minimum "distance" across which we can measure with any meaning--the universe's "maximum resolution", for shorthand--and a maximum speed--c--we end up with a minimum time.