does time travel?

[cacian]

this topic is inspired by free.



Entropy a concept I have just dipped my toes into and I am not sure I am quite there with it. thermodynamics and quantum disorder. I am not sure it is safe.

my theory is that if time travel then there could not have been a big bang. stillness create friction which causes a bang. time travels uncause the friction.
when I think time travel I thing forward never backward.

[hypatia_]

1. why do you choose to apply unequal weight to the backward passage of time, as you do forward?

2. "i am not sure it is safe" what do you mean? i think i know, but i'm not positive.

3. time travel and big bang can both exist as functional concepts, despite the belief that there was "nothing" before the bang occurred. just because you can't comprehend what the opposite of "a universe existing" is, does not mean there isn't an opposite.

4. stillness creates friction which causes a bang seems odd to me. how does stillness create friction? i get how friction could cause a bang, but according to big bang theory, at one point all the matter in the universe was contained in a single point. if it is a single point, a single unit, it cannot cause friction because it is not interacting with anything else. friction requires 2 entities interacting.

[YesNo]

I like the way you phrased the title, "does time travel". I thought entropy was the reason why there is a direction to time, but I don't know. It all reminds me of Dr. Who.

[Buh4Bee]

Does water run?

[Volya]

I always thought stillness creates the OPPOSITE of friction.

[cacian]

I always thought stillness creates the OPPOSITE of friction.

stillness condenses and therefore pushes in and out in an opposite direction. a bit like ice when it pushes hard it can eventually under the pressure of not moving.

Does water run?

depends. normally water circulates under oxygen bubble.

1. why do you choose to apply unequal weight to the backward passage of time, as you do forward?

well for me the word 'travel' means forwards. winds travel they go forward but not the opposite in one forward direction. clouds travel .they move from one spot to the next then aspire. they could not if they travelled backward.

2. "i am not sure it is safe" what do you mean? i think i know, but i'm not positive.

what do you think you know?

3. time travel and big bang can both exist as functional concepts, despite the belief that there was "nothing" before the bang occurred. just because you can't comprehend what the opposite of "a universe existing" is, does not mean there isn't an opposite.

time travel means in constant move. big bang means something stopped. there could not be an explosion if something was moving.
a bit like watching a bullet. it travels fast but it only explode because it had hit a target. it has stopped moving.

4. stillness creates friction which causes a bang seems odd to me. how does stillness create friction? i get how friction could cause a bang, but according to big bang theory, at one point all the matter in the universe was contained in a single point. if it is a single point, a single unit, it cannot cause friction because it is not interacting with anything else. friction requires 2 entities interacting.

if and when something stops means something has caused it to. friction is usually one of them. an explosion is usually because that something has stopped moving and it has complied from lack of movement to the point of an explosion.

[kev67]

Entropy is a pretty tricky subject. Temperature v Entropy graphs are used to represent thermodynamic cycles of steam pistons and turbines. The entropy of steam is greater than the entropy of water. The thing that gets me is that entropy represents disorder yet it can be measured?! or at least calculated. In metric, its units are kJ/kg.K, i.e. work divided by mass and temperature.

The concept of entropy is also used in digital communications compression techniques. More data bits are allocated the more unique a piece of information is. Very few data bits are allocated to very common pieces of information. In a picture, a patch of blue sky does not contain a lot of information, so would be compressed into few bits of data.

I read A Brief History of Time once, in which Stephen Hawking wrote that total entropy increases as time progresses. Highly ordered states tend to break down into lower ordered states. If you drop a glass it breaks into pieces. You can make another glass, but that uses more energy. The net result after making the glass is greater entropy because the fuel you used to make the glass has turned into CO2, and the chemical energy was turned to heat. The CO2 may eventually be turned back into wood via photosynthesis, but this process requires light energy from the sun. After billions and billions of years, all available energy in the universe is turned into heat energy. Heat can be still be converted into work, but only where a heat difference occurs. The larger the heat difference, the more efficient a heat engine is and the more work it can do. However heat flows from hot objects to cold objects until all are the same temperature. The heat death of the universe will occur when everything in the universe is the same temperature. The odd thing about the Big Bang according to Hawking (iirc), was that the conditions of the Big Bang represent very high entropy. Everything was mixed up and very hot. Somehow things went from very high entropy to very low entropy.

[Frostball]

well for me the word 'travel' means forwards. winds travel they go forward but not the opposite in one forward direction. clouds travel .they move from one spot to the next then aspire. they could not if they travelled backward.

That comparison doesn't really work because in space there is no forward or backward, every direction is just a direction. The only time you get a forward or backward is if you only have two directions, that is, one dimension.

time travel means in constant move. big bang means something stopped. there could not be an explosion if something was moving.
a bit like watching a bullet. it travels fast but it only explode because it had hit a target. it has stopped moving.

Be careful about talking about what MUST have happened at the big bang. We have a good idea about what happened from the planck time onward, but before that all the physics breaks down, and we really can't make any assumptions about what is physically possible during that time. You can't use your common sense assumptions about such a time, as the way the universe really works often runs very contrary to our common sense expectations.

if and when something stops means something has caused it to. friction is usually one of them. an explosion is usually because that something has stopped moving and it has complied from lack of movement to the point of an explosion.

Again, if you're talking about the big bang, you can't apply any current understanding of physics to it. Besides, the big bang wasn't even an "explosion" exactly, but an incredibly fast expansion.

[hypatia_]

Entropy is a pretty tricky subject. Temperature v Entropy graphs are used to represent thermodynamic cycles of steam pistons and turbines. The entropy of steam is greater than the entropy of water. The thing that gets me is that entropy represents disorder yet it can be measured?! or at least calculated. In metric, its units are kJ/kg.K, i.e. work divided by mass and temperature.

The concept of entropy is also used in digital communications compression techniques. More data bits are allocated the more unique a piece of information is. Very few data bits are allocated to very common pieces of information. In a picture, a patch of blue sky does not contain a lot of information, so would be compressed into few bits of data.

I read A Brief History of Time once, in which Stephen Hawking wrote that total entropy increases as time progresses. Highly ordered states tend to break down into lower ordered states. If you drop a glass it breaks into pieces. You can make another glass, but that uses more energy. The net result after making the glass is greater entropy because the fuel you used to make the glass has turned into CO2, and the chemical energy was turned to heat. The CO2 may eventually be turned back into wood via photosynthesis, but this process requires light energy from the sun. After billions and billions of years, all available energy in the universe is turned into heat energy. Heat can be still be converted into work, but only where a heat difference occurs. The larger the heat difference, the more efficient a heat engine is and the more work it can do. However heat flows from hot objects to cold objects until all are the same temperature. The heat death of the universe will occur when everything in the universe is the same temperature. The odd thing about the Big Bang according to Hawking (iirc), was that the conditions of the Big Bang represent very high entropy. Everything was mixed up and very hot. Somehow things went from very high entropy to very low entropy.

So the universe is simply approaching equilibrium. Then what? Stillness? Another bang? Hmm

[kev67]

So the universe is simply approaching equilibrium. Then what? Stillness? Another bang? Hmm

I think I read in Hawking's book that either the universe would keep expanding for ever, or eventually start contracting again into a Big Crunch. There was some conjecture that time would start running backward at that point, at least that was the plot of an episode of Red Dwarf. It depends on whether there is enough mass in the universe for gravity to start pulling everything back in. I think at the moment it has been decided that there is not enough mass to halt eternal expansion. If that is the case then eventually even the black holes would evaporate away due to Hawking Radiation. Quantum mechanic predicts that pairs of matter and anti-matter particles can just re-appear this side of a black hole's event horizon. If the anti-matter particle drifts beneath the event horizon but the matter particle escapes, the black hole is reduced a tiny little bit. Over the eons, even the black holes would cease to be. However, there are a lot of weird things that have not been got to the bottom of yet. Something was causing the universe to expand quicker than it should. Astronomers are still looking for all this dark matter. You would have to ask a professional cosmologist.

[hypatia_]

I think the universe expands to a certain point, perhaps to "stillness," then begins to contract again, and the cycle is eternal. it's like a heart beat.

[Frostball]

I believe the largest scientific consensus and the theory that most current data supports is that the universe is flat. This means that the universe is expected to continue expanding until heat death. The theory of a universe like a heartbeat was popular for some time, but we've since discovered the phenomenon of dark energy that seems to be pulling the universe apart faster and faster all the time, the expectation is for this to continue for ever.

[YesNo]

I've heard that the universe is flat also. That would mean there is no recycling of the matter in the universe in another big bang later on. However, I like the idea of a "heartbeat" to the universe. It is a metaphor that is closer to an organism than a machine. To me, the big bang seems like a cosmic egg, at least, that is how I remember reading Rupert Sheldrake describe it, but who knows how close any of these metaphors are to the truth?

If the universe isn't eternal, but has a beginning and an ultimate end, that means there is an "outside" to it perhaps containing other universes each starting with their own big bangs. If the big bang happened once, I can see it happening many times.

What does that have to do with time travel? Probably nothing, but I suspect if people were able to go back in time, we would have seen them coming back to this time or heard about them coming back in other times. So I doubt we have the ability to do so.

[hypatia_]

If the universe isn't eternal, but has a beginning and an ultimate end, that means there is an "outside" to it perhaps containing other universes each starting with their own big bangs. If the big bang happened once, I can see it happening many times.

.

I don't know if you can assume that something with a beginning and end has to have an "outside" to it. I agree with you that it's entirely possible that there are other universes also "big-banging" though.

I believe the largest scientific consensus and the theory that most current data supports is that the universe is flat. This means that the universe is expected to continue expanding until heat death. The theory of a universe like a heartbeat was popular for some time, but we've since discovered the phenomenon of dark energy that seems to be pulling the universe apart faster and faster all the time, the expectation is for this to continue for ever.

I don't think there's very much scientific evidence supporting the claim that the universe will continue expanding forever.

And the term "dark energy" irritates me. It is mostly a vague term used to fill in holes in relativity. Don't get me wrong, it definitely is labeling something that exists, but I'm not sure we are anywhere close to understanding it or it's relationship with pulling apart the universe.

[free]

I've read that time doesn't exist and that it is an illusion of our senses.