I’ve just read a New Scientist article by Paul Davies (The Black Hole Paradox) that states as a definite and unarguable fact that the “Laws of Physics” work the same in both directions of time, so time has no inherent direction.

I think that is just wrong. Entropy has a direction of time, and entropy is a result of quantum uncertainty, which is a fundamental “Law of Physics”, so why do scientists talk about time having no direction?

Maybe he meant “apart from entropy”.

Bubblecar said:

Maybe he meant “apart from entropy”.

Why would he say that though?

It would be like saying that objects on the surface of a planet have no preferred direction of motion (other than the effects of gravity).

The Rev Dodgson said:

Bubblecar said:

Maybe he meant “apart from entropy”.

Why would he say that though?

It would be like saying that objects on the surface of a planet have no preferred direction of motion (other than the effects of gravity).

Not having read the article, I don’t know. You may have to ask Dr Davies.

He’s now 75 and no longer sports a moustache.

Bubblecar said:

The Rev Dodgson said:

Bubblecar said:

Maybe he meant “apart from entropy”.

Why would he say that though?

It would be like saying that objects on the surface of a planet have no preferred direction of motion (other than the effects of gravity).

Not having read the article, I don’t know. You may have to ask Dr Davies.

I think Stephen Hawking said something about the mathematics of time not having a direction.

Tamb said:

Bubblecar said:

The Rev Dodgson said:

Why would he say that though?

It would be like saying that objects on the surface of a planet have no preferred direction of motion (other than the effects of gravity).

Not having read the article, I don’t know. You may have to ask Dr Davies.

I think Stephen Hawking said something about the mathematics of time not having a direction.

Tick Tock

Tamb said:

Bubblecar said:

The Rev Dodgson said:

Why would he say that though?

It would be like saying that objects on the surface of a planet have no preferred direction of motion (other than the effects of gravity).

Not having read the article, I don’t know. You may have to ask Dr Davies.

I think Stephen Hawking said something about the mathematics of time not having a direction.

Hawking and Penrose concluded that in a contracting universe, time would not be “going backwards”, because entropy would retain the same direction.

Bubblecar said:

Tamb said:

Bubblecar said:

Not having read the article, I don’t know. You may have to ask Dr Davies.

I think Stephen Hawking said something about the mathematics of time not having a direction.

Hawking and Penrose concluded that in a contracting universe, time would not be “going backwards”, because entropy would retain the same direction.

I always found that a funny notion that time would reverse in a contracting Universe.

Bogsnorkler said:

Bubblecar said:

Tamb said:

I think Stephen Hawking said something about the mathematics of time not having a direction.

Hawking and Penrose concluded that in a contracting universe, time would not be “going backwards”, because entropy would retain the same direction.

I always found that a funny notion that time would reverse in a contracting Universe.

How indeed could time reverse? Put the mainspring in backwards?

Tamb said:

Bubblecar said:

The Rev Dodgson said:

Why would he say that though?

It would be like saying that objects on the surface of a planet have no preferred direction of motion (other than the effects of gravity).

Not having read the article, I don’t know. You may have to ask Dr Davies.

I think Stephen Hawking said something about the mathematics of time not having a direction.

Lots of people say it, some of them well respected scientists.

I just don’t understand why they say it.

The Rev Dodgson said:

Tamb said:

Bubblecar said:

Not having read the article, I don’t know. You may have to ask Dr Davies.

I think Stephen Hawking said something about the mathematics of time not having a direction.

Lots of people say it, some of them well respected scientists.

I just don’t understand why they say it.

There is no such thing as going forward?

https://en.wikipedia.org/wiki/CPT_symmetry

https://theconversation.com/what-is-time-and-why-does-it-move-forward-55065
https://en.wikipedia.org/wiki/Arrow_of_time

Bubblecar said:

Tamb said:

Bubblecar said:

Not having read the article, I don’t know. You may have to ask Dr Davies.

I think Stephen Hawking said something about the mathematics of time not having a direction.

Hawking and Penrose concluded that in a contracting universe, time would not be “going backwards”, because entropy would retain the same direction.

Agree, things would not reverse in a contracting universe, rather all the bits that are left contract as normal.

The Rev Dodgson said:

I’ve just read a New Scientist article by Paul Davies (The Black Hole Paradox) that states as a definite and unarguable fact that the “Laws of Physics” work the same in both directions of time, so time has no inherent direction.

I think that is just wrong. Entropy has a direction of time, and entropy is a result of quantum uncertainty, which is a fundamental “Law of Physics”, so why do scientists talk about time having no direction?

Optimism as it may allow time travel

Tau.Neutrino said:

Bubblecar said:

Tamb said:

I think Stephen Hawking said something about the mathematics of time not having a direction.

Hawking and Penrose concluded that in a contracting universe, time would not be “going backwards”, because entropy would retain the same direction.

Agree, things would not reverse in a contracting universe, rather all the bits that are left contract as normal.

Is that how it is?

The energy required to reverse a universe would take more energy than to make a universe?

but why must entropy begin at a minimum

SCIENCE said:

but why must entropy begin at a minimum

it doesn’t start at a “minimum”

SCIENCE said:

but why must entropy begin at a minimum

Isn’t that the state of the universe at the beginning, we assume though don’t we.

The Rev Dodgson said:

I’ve just read a New Scientist article by Paul Davies (The Black Hole Paradox) that states as a definite and unarguable fact that the “Laws of Physics” work the same in both directions of time, so time has no inherent direction.

I think that is just wrong. Entropy has a direction of time, and entropy is a result of quantum uncertainty, which is a fundamental “Law of Physics”, so why do scientists talk about time having no direction?

I think the issue here is the distinction between what is a ‘law of physics’ and what is a ‘law of thermodynamics’ .. but I agree, it’s seems a silly distinction to make

Cymek said:

SCIENCE said:

but why must entropy begin at a minimum

Isn’t that the state of the universe at the beginning, we assume though don’t we.

entropy simply increases with time, that’s all.. it’s a statistical measure of uncertainty

My uninformed opinion is that the lack of closed time loops, the unidirectionality of time, needs to be enshrined into physics as a separate law that is even more fundamental than the laws of general relativity.

I’m thinking lately that if you take a Kerr black hole, commonly and mistakenly called a wormhole, and shrink it to its smallest possible dimension then the result will be an electron neutrino.

I’m thinking that the mass of the electron neutrino should be calculable from the laws of general relativity (perhaps or perhapns not including quantum mechnaical tunnelling). General Relativity tells us that the mass of an electron neutrino cannot be zero because it contains mass from its energy and momentum of spin. Perhaps that will give a more accurate answer then direct observation.

diddly-squat said:

SCIENCE said:

but why must entropy begin at a minimum

it doesn’t start at a “minimum”

no because you don’t agree there is a start

anyway just catching up we can say the better word is indeterminacy but hey semantics retired with the old

The arrow of time, also called time’s arrow, is the concept positing the “one-way direction” or “asymmetry” of time. It was developed in 1927 by the British astrophysicist Arthur Eddington, and is an unsolved general physics question. This direction, according to Eddington, could be determined by studying the organization of atoms, molecules, and bodies, and might be drawn upon a four-dimensional relativistic map of the world (“a solid block of paper”).

Physical processes at the microscopic level are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or flow) of time.

https://en.m.wikipedia.org/wiki/Arrow_of_time

Ian said:

The arrow of time, also called time’s arrow, is the concept positing the “one-way direction” or “asymmetry” of time. It was developed in 1927 by the British astrophysicist Arthur Eddington, and is an unsolved general physics question. This direction, according to Eddington, could be determined by studying the organization of atoms, molecules, and bodies, and might be drawn upon a four-dimensional relativistic map of the world (“a solid block of paper”).

Physical processes at the microscopic level are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or flow) of time.

https://en.m.wikipedia.org/wiki/Arrow_of_time

See that’s what I don’t get.

If you look at the interaction over time of three or more entities at the quantum level then entropy comes into the picture, so how can the interactions be time symmetric?

Could you set up an 3D timevane on a gimbal?

Peak Warming Man said:

Could you set up an 3D timevane on a gimbal?

The Internet has reminded me what a gimbal is, but it was remarkably unhelpful with information on what a 3D timevane is, so I don’t know.

The Rev Dodgson said:

Peak Warming Man said:

Could you set up an 3D timevane on a gimbal?

The Internet has reminded me what a gimbal is, but it was remarkably unhelpful with information on what a 3D timevane is, so I don’t know.

No worries.

The Rev Dodgson said:

Ian said:

The arrow of time, also called time’s arrow, is the concept positing the “one-way direction” or “asymmetry” of time. It was developed in 1927 by the British astrophysicist Arthur Eddington, and is an unsolved general physics question. This direction, according to Eddington, could be determined by studying the organization of atoms, molecules, and bodies, and might be drawn upon a four-dimensional relativistic map of the world (“a solid block of paper”).

Physical processes at the microscopic level are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or flow) of time.

https://en.m.wikipedia.org/wiki/Arrow_of_time

See that’s what I don’t get.

If you look at the interaction over time of three or more entities at the quantum level then entropy comes into the picture, so how can the interactions be time symmetric?

I don’t know any more than what Wikipedia tells me and even that’s not always TATE.

The Rev Dodgson said:

Ian said:

The arrow of time, also called time’s arrow, is the concept positing the “one-way direction” or “asymmetry” of time. It was developed in 1927 by the British astrophysicist Arthur Eddington, and is an unsolved general physics question. This direction, according to Eddington, could be determined by studying the organization of atoms, molecules, and bodies, and might be drawn upon a four-dimensional relativistic map of the world (“a solid block of paper”).

Physical processes at the microscopic level are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or flow) of time.

https://en.m.wikipedia.org/wiki/Arrow_of_time

See that’s what I don’t get.

If you look at the interaction over time of three or more entities at the quantum level then entropy comes into the picture, so how can the interactions be time symmetric?

If the universe did contract what would happen to time would it reverse and what does that mean like rewind on a video