Post by: jeffreyH on 11/11/2014 22:30:33
Post by: yor_on on 12/11/2014 11:18:43
You're correct in that, from an idea of a universe, as some sort of container holding everything there can be to us, there is no simple definition of what 'time' is. But you will find a simple definition locally, using the concept of ones wrist watch, measuring ones local 'time', from ones birth to ones death.
That local definition is shared equivalently throughout a universe.
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actually, one has no other measure, of anything, than the local definition. And that one will hold, it's also the one we use to define science, as physics. So it becomes somewhat difficult to argue that time doesn't exist, it's easier to question our ideas of containment.
Post by: PmbPhy on 12/11/2014 15:13:45
Time measures rates of change. Rates of change themselves change due to what we understand as time dilation. There is no universal time at all. If we were to imagine all the particles and fields in the universe to be frozen in one state and stepped forward by discrete amounts then points of synchronization would be distributed throughout the system. Where the particles in those areas had exactly the same 'clock' rate. This would be wavelike. The concept of time does not lend itself well to modeling this kind of system because of the need for transformations at every region of different rates of change. This is a complication in a system that appears to be more fluid than static. So as the title states, is time irrelevant?That was very unclear. In any case time is not irrelevant in any sense of the term,
Post by: jeffreyH on 12/11/2014 20:07:59
Time measures rates of change. Rates of change themselves change due to what we understand as time dilation. There is no universal time at all. If we were to imagine all the particles and fields in the universe to be frozen in one state and stepped forward by discrete amounts then points of synchronization would be distributed throughout the system. Where the particles in those areas had exactly the same 'clock' rate. This would be wavelike. The concept of time does not lend itself well to modeling this kind of system because of the need for transformations at every region of different rates of change. This is a complication in a system that appears to be more fluid than static. So as the title states, is time irrelevant?That was very unclear. In any case time is not irrelevant in any sense of the term,
Well then Pete I have failed. I wanted to stimulate a debate. If I can't make my points clear we'll get nowhere.
Post by: RTCPhysics on 12/11/2014 22:23:00
Time is arguably the most powerful concept that we have today, but it is a concept rooted firmly in our human psyche, explaining periodic events such as: birth and death, night and day, winter and summer and movement from place to place.
Through the centuries, we have gained the ability to measure time more and more accurately, using objects with a periodic motion, such as the quartz crystal which vibrates under an applied voltage or the microwave emissions from the caesium atom. But why is 'periodic motion' so fundamental to the physics of the Universe! Clocks are just physical entities, like any other.
If you wished to argue for the retention of the concept of time, you may point out that without 'time' all the past and future events would kaleidoscope, time being the axis upon which all events are plotted. However, by perceiving universal change as occurring in a sequential manner for all matter and radiant energy simultaneously, then the order of events in the Universe is maintained. It is this, that is the true reality and time is just a human invention to manage the process of change more effectively. Put another way, you can detect change, but you cannot detect the passage of time.
So take a minute to think about this. How did an inanimate object such as our universe, acquire the concept of time and time intervals? And if it could, did it require the concept to create all the elements of the Periodic Table which make up the content of our Universe? If you come to the conclusion that an inanimate object couldn't conceive of time, then you must accept that time and time intervals are just a human concept, which we've invented to manage the processes of change that we initiate and those forced upon us, in a more effective manner.
If we abandon the concept of time from our thinking, then how do we view the ongoing changes which we see about us every second of the day. The main observation that we can make is that change happens in a sequential fashion and cannot be erased or reversed. For example, if you walk across a field of grass and back again, the future for the grass that you have crushed underfoot will never be the same again. Everything lives by observing or sensing the changes that are happening in the world around them.
Accepting the idea that time doesn't exist, means giving up the notion of beginnings and ends. So, viewing the Universe through the concept of 'sequential universal change', leads to the realisation that the Universe has had no beginning and has no end, it just changes form continuously in a discrete manner, however many "big bangs" that might be. But this is not to say that time and time intervals is not a brilliant human invention and a valuable tool in ordering past events. Just be aware of thinking of it as a real physical quantity. It isn't.
Post by: jeffreyH on 12/11/2014 22:46:16
Post by: alancalverd on 12/11/2014 23:35:51
Time measures rates of change.
No! Rate of change is dx/dt, i.e. has dimensions of x/time.
Time is what separates sequential events.
Post by: jeffreyH on 13/11/2014 00:48:42
Time measures rates of change.
No! Rate of change is dx/dt, i.e. has dimensions of x/time.
Time is what separates sequential events.
OK so I didn't state it in the correct way.
Post by: Ethos_ on 13/11/2014 01:14:16
Clever way of defining time alan;Time measures rates of change.
No! Rate of change is dx/dt, i.e. has dimensions of x/time.
Time is what separates sequential events.
"The interval between sequential events."
This raises a question I need some help with. Does the measure of Planck time place a limit on that interval? I've heard it argued both ways, one suggesting that "Planck time is only the interval we can successfully measure." And the other position; "Planck time is truly the shortest length of time possible." I would appreciate hearing everyone's view on the question.
Post by: Bill S on 13/11/2014 19:09:44
Quote from: Ethos
This raises a question I need some help with. Does the measure of Planck time place a limit on that interval? I've heard it argued both ways, one suggesting that "Planck time is only the interval we can successfully measure." And the other position; "Planck time is truly the shortest length of time possible." I would appreciate hearing everyone's view on the question.
Let’s start with a “hitch-hiker’s” thoughts.
Do we have any concrete evidence that time is quantized? I think not.
Do we have any concrete evidence that Planck’s time cannot be divided? Not that I am aware of.
Can we measure an interval as small as Planck’s time? Not with our present instruments.
Is "Planck time [is] truly the shortest length of time possible." We don’t know (yet).
Post by: RTCPhysics on 13/11/2014 20:05:17
Post by: jeffreyH on 13/11/2014 22:11:53
If you want to take out the concept of 'time dilation', you have to take on Einstein's theory of special relativity.
I don't want to do that. I want an equation of the form
in three dimensions. Here energy is not simple to describe. The components of mass, potential and kinetic energy interact with the gravitational field.
Post by: PmbPhy on 14/11/2014 02:17:10
Quote from: alancalverd
No! Rate of change is dx/dt, i.e. has dimensions of x/time.He didn't say that time is a rate of change. He said that one uses time to quantify rate of change.
Time is what separates sequential events.
Post by: yor_on on 14/11/2014 10:47:50
"In principle, a black hole can have any mass equal to or above the Planck mass (about 22 micrograms). To make a black hole, one must concentrate mass or energy sufficiently that the escape velocity from the region in which it is concentrated exceeds the speed of light. This condition gives the Schwarzschild radius, R = 2GM/c^2, where G is the gravitational constant and c is the speed of light, and M the mass of the black hole. On the other hand, the Compton wavelength, where h is Planck's constant, represents a limit on the minimum size of the region in which a mass M at rest can be localized." https://en.wikipedia.org/wiki/Micro_black_hole#Minimum_mass_of_a_black_hole
What's under Planck scale is a rather mysterious place to me :) where a lot of mathematical definitions, as well as physics, seems to lose their meaning. http://math.ucr.edu/home/baez/planck/node2.html and then http://backreaction.blogspot.se/2013/04/black-holes-and-planck-length.html as some examples.
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Eh, should just have posted this one maybe?
Never too late though. The Planck length as a minimal length. (http://backreaction.blogspot.se/2012/01/planck-length-as-minimal-length.html)
She's pretty smart that Bee.
Post by: yor_on on 14/11/2014 11:32:55
"The “Planck length” is the unit of length in Planck units, and it’s ** meters. Which is small. I don’t even have a remotely useful way of describing how small that is. Think of anything at all: that’s way, way, way bigger.
A hydrogen atom is about 10 trillion trillion Planck lengths across (which, in the pantheon of worldly facts, ranks among the most useless)." http://www.askamathematician.com/2013/05/q-what-is-the-planck-length-what-is-its-relevance/
The question of a physical discreteness may be at that scale, on the other hand you have HUP coming into play far above it. As I tend to think you can be of two minds here, both making perfect sense co-existing. One is HUP (Heisenberg's uncertainty principle) telling me that the universe may be 'consistent' after my measurement, but before it? And that one holds true. The other is the idea of a smallest 'length' in where we all would like to see if it exist, and as Planck scale is about both time, mass and length inseparably, it becomes a question of granularity (discreteness) to me, and of our possibility of measuring such a one. There HUP cloak this question for me, unless you presume 'weak experiments' to be 'practical proofs', which also is the main reason why some want it to be proofs. That's not clear thinking to me, it's more of a wish of the universe to make a 'clock work sense' in the fashion of our forefathers (and mothers:) thoughts.
The question why it's not what I like to consider clear thinking belongs to a multitude of reasons. One is that it presumes, and the mirror to it is that with a causality existing you must find 'proofs'(although not singularly made local experiments proving the same), forgetting that without causality we wouldn't be here, at least not together. And there are some more, as using repeated experiments calling them 'equivalent' ignoring what differs them, or defining it such as your action (your weak measurement) do not have a reaction on what you measure indirectly. But the first two is sufficient to me for questioning this idea. Causality becomes a logic, but with inflation, expansion, and a lot of the basic principles (assumptions) we build physics from, not having been disproved yet, this logic may become a lot weirder than anything our ancestors expected.
Myself I'm more and more wondering what HUP really says about a universe?
Post by: RTCPhysics on 14/11/2014 18:40:53
Do we have any concrete evidence that Planck’s time cannot be divided? Not that I am aware of.
Can we measure an interval as small as Planck’s time? Not with our present instruments.
Is "Planck time [is] truly the shortest length of time possible." We don’t know (yet).
These comments equally apply to length and dimensions.