How old is the universe?

[Asmodean]

Do illusions exist?
What are the mechanisms by which they function?

[zorkan]

In the quantum world illusions do exist.
It also suggests that in the quantum universe time does not exist.
Only in Einstein's universe does time exist.

Correction. I should have said Plato's cave allegory.
https://medium.com/mind-cafe/platos-allegory-of-the-cave-provides-a-sobering-look-at-human-ignorance-ffe1cd54ee96

[Asmodean]

In this sense, what is the difference between Einstein's universe and quantum universe?

[zorkan]

Time is relative according to Einstein.
That's why I admire photons. Unlike me they don't appear to age.
"From a photon's perspective, it can pass through the entire Universe without experiencing time at all. Billions and billions of light-years can fly by, in far less than the blink of an eye."

[Asmodean]

Well... Yeah. But that does not in any way speak to a fundamental difference between "quantum universe" and "Einstein's universe." I mean, if we were talking about gravity or some such, but time..?

Time is relative because it can be affected by speed and gravity, the latter potentially describable as a parameter in the shape of spacetime, which "all" massive objects have/are subjected to. Photons are massless, so in the frame of reference of a photon, time is... A scalar, I suppose. It's still there for that. Still relative to the frame of reference.

[zorkan]

In Einstein's universe time goes forward.
In Feynman's it can go backward as in the case of antimatter.
Tachyons might also go backwards.
It's as if there are 2 universes out there.

https://en.wikipedia.org/wiki/Retrocausality#:~:text=Hypothetical%20superluminal%20particles%20called%20tachyons,in%20a%20conventional%20reference%20frame.

[Asmodean]

In Einstein's universe time goes forward.
In Feynman's it can go backward as in the case of antimatter.
Tachyons might also go backwards.
It's as if there are 2 universes out there.

https://en.wikipedia.org/wiki/Retrocausality#:~:text=Hypothetical%20superluminal%20particles%20called%20tachyons,in%20a%20conventional%20reference%20frame.

Could you substantiate the Einsteinian universe necessitating unidirectional time? Because from what I understand, general relativity absolutely permits time travel (also in reverse) - even necessitates it in cases of objects traveling at subluminal speeds within their localised frames of reference.

[zorkan]

I will only work off the 2nd law.
https://newsroom.carleton.ca/story/can-we-time-travel/#:~:text=Time%20travel%20also%20violates%20the,you%20cannot%20unscramble%20an%20egg.

Even as a human gets older time quickens and in one direction only.
 

[Asmodean]

I will only work off the 2nd law.

There are several things that can be described as the "2nd law." In this instance, the most obvious examples are motion and thermodynamics. From the link you provided, I assume the latter, but the source is flawed to the point of wrongness when taking the conversation to the level you appear to want to operate at.

One point of contention is that they do not specify what kind of a system they are referring to. Do they claim that time travel violates the second law of thermodynamics for the traveler, the region of space, the universe? A closed system or not? (Is energy being added?)

In the latter case, I give you a humble pile of lego blocks which, if the proper input of energy is provided, can result in a highly-ordered lego skyscraper.

Another issue is that entropy within a closed (meaning energy-isolated) system must not always increase - what it is, is statistically likely to do so.

Moreover, they say crap like "a negative mass tennis ball would fall upward if dropped." While not precisely false, it is also not true. Given no other forces, the ball would fall away from positive mass. Whether that direction is "up," is arbitrary. (Decided by the direction of arrows in the coordinate system)

It's not a bad article, but it is written for a very casual reader, so when you say that you would;

only work off the 2nd law.

...And then use that as your source, I must urge you to reconsider your parameters.

[zorkan]

It suggests that time travel to the past breaks the 2nd law and therefore cannot happen.
The grandfather paradox backs that up.
You are never going to rearrange all the particles in the universe to enter the past, or arrange them for the future.

[Asmodean]

Well, the second law of thermodynamics is not a problem in itself. You can certainly achieve localized "negative entropy" by adding energy to the system. Heck, that's how you stay alive.

Grandfather paradox is on the profound side of thought experiments, and calls for some more outlandish solutions like non-linear causality (time "moving" forward or back is linear)

[zorkan]

2nd law explains how you came out of the darkness and why you will return to it.
For the darkness you can substitute the chaos.

DNA molecule was likely to form sooner or later by some probabilty given the right conditions.
It doesn't rule out some sort of super DNA in the future.

[Asmodean]

2nd law explains how you came out of the darkness and why you will return to it.
For the darkness you can substitute the chaos.

It really does not. You could use it way outside its scope like that, but the second law of thermodynamics does not speak to darkness or chaos. What it does is state that without the input of energy, a system will degradee from "useful" to "useless" given enough time. When the sun fuses hydrogen, the energy is converted and a bunch is "lost" in forms that "don't do anything." Some of it hits a leaf and helps a tree grow, again incurring losses. Then you burn that tree for warmth, converting it into heat and ash. So on. Even at this stage, very little of what the Sun put out remains in a form that allows it to "do something" other than move through space at the speed of light. That is entropy in practice, if somewhat clumsily exemplified.

What it says about you is that you are an open system. You have an input of energy that keeps you "useful"

(Here, "useful" and "useless" are with regard to the ability and relative likelihood to, without further input of energy, interact and further convert the existing energy from one state to another)

DNA molecule was likely to form sooner or later by some probabilty given the right conditions.
It doesn't rule out some sort of super DNA in the future.

Thermodynamically speaking? No, I suppose it does not, but how is this relevant to the discussion at hand?

[zorkan]

"What it says about you is that you are an open system. You have an input of energy that keeps you useful"

Spotted your deliberate mistake!
We are closed systems.
If the universe is bounded it's also a closed system, if unbounded an open one.

[Asmodean]

"What it says about you is that you are an open system. You have an input of energy that keeps you useful"

Spotted your deliberate mistake!
We are closed systems.
If the universe is bounded it's also a closed system, if unbounded an open one.

No. A human is, thermodynamically-among-other-things-such-as-the-system-thory-but-let-us-not-dwell speaking, an open system. If you think otherwise, I challenge* you to forego eating, drinking and breathing - conversely, urinating, sweating and defecating - and see how well it goes.

*"Mandatory" disclaimer: Literally speaking, I do no such thing. Don't suffocate (Or dehydrate or starve or otherwise harm or even seriously discomfort) yourself on my - or anyone's - account. ;-)

The Universe may or may not be an open system - it depends on the scope at which you look.