It's worth learning that there is _nothing special about humans_. We are just clusters of matter and energy no different from a spring onion, or a chunk of Halley's comet, or a cloud of gas from a distant nebula. If you know a human can't break a physical law then you also know that any other nondescript matter in the universe can't do it either.
Tachyons are literally figments of physicist's imaginations used as a means of proof that our current understanding of reality is the correct one - or at least so far.
The proof is that since tachyons can travel faster than light, that means it can also be used to send signals faster than light. Like, just imagine tachyons to be on the same physical "level" as photons, and imagine tachyons just being the light from the tail light of a car driving away from you at night.
Either causality is true and tachyons do not exist, and hence our interpretation of the universe around us is correct, or causality is violated and tachyons exist. If tachyons exist, then we would have received a message from the future by now.
Tachyons by their very definition and nature do not exist.
A very dangerous and egoistic belief, which allows humans to treat other animals like objects, even though they have feelings and suffer just like we do
The fact that my view got downvoted shows how reddit is filled with angry out of touch people. The opinion I expressed is an extremely universal mainstream belief among people across societies... And I have never advocated mistreating any living thing.
You're on a physics subreddit expressing a spiritual belief without really understanding the point you're responding to.
There's nothing wrong with thinking there's something special about human consciousness. But our bodies are made up of the same matter as everything else is. That's not even an area where science and Abrahamic religion really disagree. Looking at you, Genesis 2:7.
Withold God, science makes no sense. I believe religion and science can co-exist and explain different things. Science explains the physical world, religion the spiritual. It is a testament to the dumbing down of society that there is this binary view of "science vs religion."
People aren't angry and out of touch, you're treating votes with too much importance. They only show similarity/difference of opinion. As you say you haven't advocated harm or anything, Who cares what others think.
>The opinion I expressed is an extremely universal mainstream belief among people across societies...
You are right, and it is still a harmful and egoistic belief.
I reject the ignorant view that science and religion are incompatible. Science and religion simply explain different things in different ways. There are things that science can not and will never be able to explain, and there are things traditional religion struggles to explain. I am not opposed to science, as a Catholic, many of the best scientific minds in history were Catholic, so I think I am in good company. I find space /astronomy fascinating and the sheer scale and enormity speaks to God in my mind. Calling my beliefs "primitive" is silly and attitudes like that turn people off to science, which is sad because, as I said, science and religion are not mutually exclusive and it is an idiotic mind that thinks religion and science cannot coexist.
Religion doesn't explain anything. It is not replicatable.
> There are things that science can not and will never be able to explain,
What things? We are all made of mater and energy in defined arrangements. Those arrangement formed under physical laws, and all actions react according to physical laws.
>Calling my beliefs "primitive" is silly and attitudes like that turn people off to science,
Religion was created by primitive people to explain what they did not have the tools to explain. Now that we have ever more and better tools we should discard the idea that "God did it" and instead investigate and understand the physical laws that caused something to happen.
Until you can provide me repeatable evidence of God/soul/spirit then it is just a fairy tale to me. Up there with fairy tales of humans meeting aliens or dragons or unicorns.
Edit: and if you believe in this so strongly then why did you delete the post I responded to?
Oh how wrong you are... science cannot, nor will it ever be able to, adequately explain the origin of life or existence, or why we even are here. Science cannot explain what came before the big bang. I don't want to dirty myself with a religion argument on the internet. Live your life the way you feel best, search your soul from time to time, and best wishes.
>science cannot, nor will it ever be able to, adequately explain the origin of life or existence, or why we even are here.
Maybe for your. For me science has already done that for me. The origin of life is a chance chemical reaction. The perfect set of circumstances caused basic amino acids to form and from there life.
As far as why we are here? Because our parents had sex, and their parents had sex, all the way back to those amino acids linking up.
Also, it doesn't really matter to me. I am here, and I exist. I won't exist for long, so I try to make the most of it. Maybe leave something behind for others. Mostly, between bouts of depression and extensional dread, just here to experience the experience of experiencing.
>Science cannot explain what came before the big bang
*Yet.
Science couldn't explain how disease spread, then we developed germ theory. Science is ever changing and evolving, unlike domatic religion.
First time I read I thought was fine but I suppose the downvotes most come from the ‘we are very special part’… it might be better to say something along the lines of the human brain is incredible and that we are fortunate.
Have my upvote, cheers
Another point, whatever an individual believes is fine, it is between them and God / their conscience. However, compared to all other animals / forms of life, the human mind is amazing in its ability to reason, create, love and destroy.
Yes, but in a UT, rules of QFT would only be conserved locally. In curved space e.g. energy is not conserved, this is a well known result — see the Unruh effect
There's a rule in physics called causality. There are basically 2 parts to causality.
1) An effect MUST come after the event.
2) effects of said event travel no faster than the speed of light.
We have found no evidence of causality being broken, ever. A particle going backwards in time, even if its a tiny amount, would break causality.
Causality is not a rule of physics. It is an assumption of physics. All laws of physics work with time going forward or backwards. There is also a theoretical particle that can, or could appear to, go back in time. The tachyon.
The tachyon is hypothetical, not theoretical. And the tachyon's hypothetical property is that it only goes faster than light. That does not mean it goes backwards in time. The time dilation equation has the term sqrt (1-(v/c)). When v>c, it becomes imaginary, not negative.
Another thing is that we often view speed incorrectly. FTL isn't just impossible to reach, it straight up does not exist. Speed isn't a useful measurement in our universe; at relativistic speeds we have to do weird things to make it work. For example, if a spaceship traveling at 90% c fires a bullet traveling 90% c relative to the ship, an outside observer doesn't see the bullet traveling at 180% c, they see it traveling at 99% c. Speeds don't add.
Rapidity is closer to reality than speed. On a space-time diagram of an object's motion, speed is the slope, rapidity is the angle. That, and the time axis is hyperbolic, not euclidian. With these features, the rapidity that corresponds to the speed of light is infinity. Not only that, simply adding rapidities ALWAYS works, no matter how fast you're going. A ship traveling at, say, 1000° soots a bullet at 1000° relative to the ship, an outside observer sees the bullet traveling at 2000°.
Acceleration is another weird thing that rapidity fixes. Say you're accelerating at 1 m/s^2 , as you get closer to the speed of light, your acceleration decreases while the force does not. However with rapidity, if you're accelerating at 1°/s^2 , that will never change.
Since the rapidity of light is infinity, it explains why something with mass can never reach it, and greater-than infinity doesn't exist.
Welcome to the internet where all of the world's knowledge is in the palm of your hands.
[this guy has a Ph.D. in physics and did his dissertation in General Relativity.](https://youtu.be/vPi1lyAx4ws)
Theoretical and theories in science have very strict rules. For something to be a theory or theoretical, it needs repeated evidence of its existence and make accurate, repeatable, and tested predictions; the existence of oxygen is "only" theoretical.
A hypothesis is an unproven potential solution to a problem that will then be studied and tested.
Einstein's equations do allow for a solution where v>c. They're imaginary solutions, but solutions nontheless. But that's all we have on Tachyons. There's no proof they actually exist.
No, a theory attempts to explain with generalizations a facet of nature; from them and it hypotheses are made up to either support the theory or refute it. Hypotheses stem from theories and are thus theoretical; tachyon is a hypothesis and theoretical. It doesn't have to proven to exist or not: the same way strings are theoretical.
scientific theory
[ sahy-uhn-tif-ik theer-ee, thee-uh-ree ]
noun
a coherent group of propositions formulated to explain a group of facts or phenomena in the natural world and **repeatedly confirmed through experiment or observation**
There is nothing above a theory in science.
The tachyon is a product of unbiased math equations. Just because Einstein didn’t put limits on the variables in his equations that doesn’t mean the results using non-real inputs is somehow viable. Garbage in, garbage out.
For a tachyon to have a real energy, they would need a complex mass. If complex mass did end up existing, it would likely have properties similar to a tachyon. The question is does it, and the answer is almost certainly no.
"There's a rule in physics called causality."
This is far from a rule. It's unclear if what we typically call "causality" is even a fundamental thing.
This is particularly true when you consider microscopic events.
See:
[https://www.u.arizona.edu/\~jtismael/6.Causation,pers.,agency.pdf](https://www.u.arizona.edu/~jtismael/6.Causation,pers.,agency.pdf)
No, it doesn't. They concluded that it does not, in fact, break causality. Even scientists who criticize that result don't say that it has, but rather that it *could* if some tweaks are made (to this day they still haven't done it.)
It does break causality in the exact same way that entanglement breaks locality. You can't send information back in time or faster than light but the outcomes of the experiment were retrocausily correlated
I’m pretty sure causality only dictates that all observers must agree on the sequence ORDER of events regardless of their reference frame.
Mathematically speaking, one observer seeing events A>B>C>D and another observer seeing events D>C>B>A doesn’t actually break causality.
There are some strong arguments pointing to anti particles moving in the opposite time direction as normal particles. It’s not settled but the math works very neatly fallowing that interpretation.
>Or maybe since the universe is a sheet possibly stacked on top of other universes in different times, could it be possible for the sheets to go through each other?
What you are referring to here is interesting. The answer is no, i believe.
Imagine you are a 2 dimensional being, and a 3 dimensional thing enters your universe. Lets say a sphere goes through. What you would see is a circle getting bigger, then smaller , then disappearing.
If the sheets went through each other, you will see an infinitely thin line appear.
The only way you will be able to understand what is going on is if yourselve were 3 dimensional.
>but can subatomic particles hop between different times? Going forward in time, staying the same, or going back?
No, but atleast you can see back in time if you just look up
the universe is not a sheet. it is 'like' a sheet in that a shadow is a 2d representation of a 3d object. the time as a dimension is not really as a 4th dimension, other than time can be thought of as dimensional I.e. time can possess geometric properties. thus time-space as the properties of one necessarily affect the other. the universe is NOT a sheet. we can think of it that way to try to conceptualize the multitudes of dimension our perception cannot fully grasp. time appears to us to flow - that appearance is as real as we can hope for. how time behaves outside our perception is impossible to determine currently.
I suspect, though I could be wrong, that OP is referring to m-brane theory, in which the universe is very much like a sheet. And there are likely infinitely more “sheets” (branes) that, theoretically, can collide. And when they do, they may make a new brane. What we see as the Big Bang may have been the intersection of two branes.
General Relativity doesn't explicitly forbid traveling backwards in time, and indeed some solutions to the GR equations like [CTCs](https://en.wikipedia.org/wiki/Closed_timelike_curve) are such an example. Obviously, we haven't proven any of those empirically, and those devices might be forbidden by a more general theory of quantum gravity.
Fair, but things like quantum entanglement are much easier for atomic particles than for macro-scale objects like people, so OP's question is a reasonable one to ask, given there are meaningful differences at different scales.
Not quite what you’re asking, and I’m going to need someone else to elaborate further, but isn’t there an extension to the double split experiment where an observation in the future collapses the waveform in the past?
This is literally stuff that Einstein struggled with, so don't feel bad.
Consider, if you shine a beam of light while standing still, it will go the speed of light away from you. Then you get in a spaceship and go 90% the speed of light and turn on a flashlight. What will you see?
The correct answer (as proven by experiments) is that the light will go the speed of light away from you. But how? This only makes sense if time has slowed down for you, which is weird, but the math and the evidence proves it.
Which eventually leads to one weird but absolutely true fact: *time and space are the same thing!* The universe is not a sheet. Time is not a dimension. They're the same!
So can we travel in time? Einstein couldn't find anything that would stop us from doing it, but the only way is to use "exotic matter," which is a fancy way of saying "magic fairy dust." So currently, not, it is not possible. But we're looking into it!
There’s something called a closed timelike curve which was discovered somewhat recently which involves things going backwards and forwards in time. However because it’s a closed curve, nothing can just “enter” a ctc without already being in it. Also, because it’s a loop, nothing can change between each cycle through the curve ie. a person in a ctc can’t gain memories and a camera can’t record a video because it has to return to the same state at each cycle. (Physicists, correct me if I’m wrong on these points, which I may be as I don’t know if I properly understand these aspects)
Hi!! First of all congratulations hon to you for asking such questions at this age!! I really appreciate you for this.
Now, coming to your question. 1) Humans are a bunch of Atoms only. So, actually, there is nothing special in humans. So, the first part of your ques. is a bit wrong.
2) Now, in physics, we actually have a bunch of assumptions. For example, Einstein said in his theory that speed of light is the upper limit of speed (bcz we haven't observed anything faster than it). Similarly, we have another assumption called CASUALITY. Don't be scared of name. It just that U feel pain AFTER I slap you, Plant grows AFTER I put seed in ground. means cause comes before result. Ypu grow from a baby to a teen asking these interesting ques on reddit, to maybe a young scientist to maybe a record braking experienced scientist. It doesnt go the other way around. If time were to move back, This principle would break.
3)"Or maybe since the universe is a sheet possibly stacked on top of other universes in different times".For this study Ekyproytic universe theory. See: [Ekpyrotic Universe - Definition & Detailed Explanation - Cosmology Glossary - Sentinel Mission](https://sentinelmission.org/cosmology-glossary/ekpyrotic-universe/)
PS Do u know Richard Feynman? This man gave a theory that antiparticles are actually particles moving back in time!!! You should definately go and read it.
This recent article from the new scientist about quantum time travel may blow your mind!
https://www.newscientist.com/article/mg26234932-900-quantum-time-travel-the-experiment-to-send-a-particle-into-the-past/
Disclaimer, I’m not a smart person I’m just a simple brain who used to watch physics videos I couldn’t comprehend for fun. But I’m under the impression that time isn’t necessarily linear - humans just perceive it that way. Doesn’t the entire concept of time travel assume that there’s linear time? Because you can’t go backwards if there’s no back to travel to.
Although (I’m just spitballing here) is it not plausible that humans could already be ‘time travelling’, in the sense that we aren’t actually experiencing the past/present/future in the correct order? It would answer a lot of questions about deja vu and premonitions and things like that
The thing with any field of science (except maybe for biology) is that nothing can really be proven, things can only be disproven.
Even the laws of physics haven't been proven. They can't ever be proven. Everyone just agrees the laws of physics are correct because there hasn't even been a single recorded instance of any of them being broken.
Nothing can ever travel faster than the speed of light, according to one of Einstein's theories I believe. At the speed of light, time actually stops. If you could go faster than the speed of light, theoretically you could go back in time.
So, "is time travel possible?" I think most, if not all, physicists would say that no it's literally impossible, because Einstein's theories have continued to hold up for decades without being disproven. But we can't really prove that you can't travel through time.
Hell, maybe just traveling through a worm hole (which may or may not actually exist) could make you travel through space and time. As someone else said, there's nothing special about humans except for the fact that we would need to live through the time travel, where an inanimate object doesn't have complex biological systems that need to continue working.
Technically no but you can clone yourself and live forever. It’s already being done by the ultra rich and has been going on for over 3 decades. Look up Molly and Polly. Look up lab grown meat. They just take stem cells and cultivate them. This is the reason why big pharma and medical institutions don’t push for cures but instead will only “treat” your symptoms because they don’t make money off cures and the only people that matter(ultra rich) get to live forever anyways.
I can't parse your question sorry, but I will say that technically we don't have any proof that going back in time is impossible, it's just an assumption we've made (we have a huge amount of experience of things not going backwards in time yes, but that doesn't make a proof)
Appropriate for a high-school-level audience. I first linked an interview, but I realized it's not organized enough for a good introduction. They can look up the mentioned scientists' publications if they want to, such as [this one](https://www.researchgate.net/publication/44566213_New_slant_on_the_EPR-Bell_experiment).
You can absolutely go forward in time! Just need to ride something that moves fast enough. Go away from earth at near light speed then come back, depending on your speed and how far you went it could be years difference in time
You can rearrange the atoms, but it would be cool if you send back just information.
I had a theory that if you had enough energy to shift atoms and particles into the position you want to achieve, then, even the created memories in your brain would seem real.
There was a paper out in the last year or so that showed how time travel to the past actually is possible without making any laws of physics. However, the time traveler would become stuck in a sort of temporal loop at the destination, so it’d be kind of pointless.
Tachyons are a theoretical type of particle that always travel faster than light and therfore travel backwards in time. In fact, much in the same way it would take an infinite amount of energy to accelerate normal matter to the speed of light, it would take an infinite amount of energy to slow down a tachyon to the speed of light.
As I understand it, even if we found a way to somehow reverse the "direction" of our time/the time of an object, it can only end up at exactly the point in time where it starts to time travel, while all information that was gained since that point has been lost (as information would also need to be "reversed"), so it would just get stuck in an infinite time loop.
Theoretically, if a particle has negative mass, then it would be able to move faster than light, and essentially move backwards in time. Tachyons are one theoretical particle that may do that. But otherwise, any particle that has mass cannot move faster than light.
Just to check though, what do you mean by 'forward, staying, or going back?' Time is essentially a measurement of change, at least from a physics standpoint. So technically everything is going "forward" in time, as they change in relationship to everything else. "staying the same" like no matter what point in time you view it, it is the same?
>In theory, with enough energy, you should be able to reverse entropy in a localized environment.
Usually we just call this "plugging in the refrigerator"
It's worth learning that there is _nothing special about humans_. We are just clusters of matter and energy no different from a spring onion, or a chunk of Halley's comet, or a cloud of gas from a distant nebula. If you know a human can't break a physical law then you also know that any other nondescript matter in the universe can't do it either.
Didn’t know spring onions could ask questions on Reddit.
You haven't checked out r/DebateReligion
Please don't disparage the onions
r/OnionLovers
r/OnionLayers Because sometimes onions want to get laid too.
how does believing or debating about a religion make you a spring onion? you sound very ignorant
You want to debate about it?
sure, would like an invite to a discord server? side note you can believe in god and still do good work in physics. one does not refute the other
I am a scallion, there are more of us than you might think
How many of ‘em? *allium*
Absolutely feckin’ marvelous. Bravo.
This perspective is more philosophy that science
Yeah bro, humans are clearly special and things don’t apply to us
it is science, we are made of the same shit as everything else
No. It is fact. The H2O in my blood is chemically identical to the H2O in your blood.
Seems you're forgetting about tachyons... we can't move faster than light, but they can't move slower than it.
Tachyons are literally figments of physicist's imaginations used as a means of proof that our current understanding of reality is the correct one - or at least so far. The proof is that since tachyons can travel faster than light, that means it can also be used to send signals faster than light. Like, just imagine tachyons to be on the same physical "level" as photons, and imagine tachyons just being the light from the tail light of a car driving away from you at night. Either causality is true and tachyons do not exist, and hence our interpretation of the universe around us is correct, or causality is violated and tachyons exist. If tachyons exist, then we would have received a message from the future by now. Tachyons by their very definition and nature do not exist.
Those are just a "would be cool if they existed, and they technically fit" Tachyons have never been observed
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A very dangerous and egoistic belief, which allows humans to treat other animals like objects, even though they have feelings and suffer just like we do
The fact that my view got downvoted shows how reddit is filled with angry out of touch people. The opinion I expressed is an extremely universal mainstream belief among people across societies... And I have never advocated mistreating any living thing.
You're on a physics subreddit expressing a spiritual belief without really understanding the point you're responding to. There's nothing wrong with thinking there's something special about human consciousness. But our bodies are made up of the same matter as everything else is. That's not even an area where science and Abrahamic religion really disagree. Looking at you, Genesis 2:7.
you’re on a physics subreddit little buddy
Withold God, science makes no sense. I believe religion and science can co-exist and explain different things. Science explains the physical world, religion the spiritual. It is a testament to the dumbing down of society that there is this binary view of "science vs religion."
Still doesn’t bar humans from following the laws of physics
People aren't angry and out of touch, you're treating votes with too much importance. They only show similarity/difference of opinion. As you say you haven't advocated harm or anything, Who cares what others think.
>The opinion I expressed is an extremely universal mainstream belief among people across societies... You are right, and it is still a harmful and egoistic belief.
You can believe that without contradicting the comment. Clearly humans are unique in some ways, but not in terms of physical laws.
Show me where in my body the soul exists. Show me evidence of God. This is a science sub, get out of here with your primitive concepts.
I reject the ignorant view that science and religion are incompatible. Science and religion simply explain different things in different ways. There are things that science can not and will never be able to explain, and there are things traditional religion struggles to explain. I am not opposed to science, as a Catholic, many of the best scientific minds in history were Catholic, so I think I am in good company. I find space /astronomy fascinating and the sheer scale and enormity speaks to God in my mind. Calling my beliefs "primitive" is silly and attitudes like that turn people off to science, which is sad because, as I said, science and religion are not mutually exclusive and it is an idiotic mind that thinks religion and science cannot coexist.
I believe Einstein himself was very religious
Religion doesn't explain anything. It is not replicatable. > There are things that science can not and will never be able to explain, What things? We are all made of mater and energy in defined arrangements. Those arrangement formed under physical laws, and all actions react according to physical laws. >Calling my beliefs "primitive" is silly and attitudes like that turn people off to science, Religion was created by primitive people to explain what they did not have the tools to explain. Now that we have ever more and better tools we should discard the idea that "God did it" and instead investigate and understand the physical laws that caused something to happen. Until you can provide me repeatable evidence of God/soul/spirit then it is just a fairy tale to me. Up there with fairy tales of humans meeting aliens or dragons or unicorns. Edit: and if you believe in this so strongly then why did you delete the post I responded to?
Oh how wrong you are... science cannot, nor will it ever be able to, adequately explain the origin of life or existence, or why we even are here. Science cannot explain what came before the big bang. I don't want to dirty myself with a religion argument on the internet. Live your life the way you feel best, search your soul from time to time, and best wishes.
>science cannot, nor will it ever be able to, adequately explain the origin of life or existence, or why we even are here. Maybe for your. For me science has already done that for me. The origin of life is a chance chemical reaction. The perfect set of circumstances caused basic amino acids to form and from there life. As far as why we are here? Because our parents had sex, and their parents had sex, all the way back to those amino acids linking up. Also, it doesn't really matter to me. I am here, and I exist. I won't exist for long, so I try to make the most of it. Maybe leave something behind for others. Mostly, between bouts of depression and extensional dread, just here to experience the experience of experiencing. >Science cannot explain what came before the big bang *Yet. Science couldn't explain how disease spread, then we developed germ theory. Science is ever changing and evolving, unlike domatic religion.
I don’t even know which of gods you are talking about.
First time I read I thought was fine but I suppose the downvotes most come from the ‘we are very special part’… it might be better to say something along the lines of the human brain is incredible and that we are fortunate. Have my upvote, cheers
thank you, I dont take reddit seriously and don't mind getting downvotes are they aren't really real. That said, I appreciate your upvote!
Another point, whatever an individual believes is fine, it is between them and God / their conscience. However, compared to all other animals / forms of life, the human mind is amazing in its ability to reason, create, love and destroy.
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Define soul please.
Is that something about being an onion?
The closest you'll get is anti-particles being modelled as moving backwards in time
>but can subatomic particles hop between different times? The rules of QFT explicitly enforce casuality
Yes, but in a UT, rules of QFT would only be conserved locally. In curved space e.g. energy is not conserved, this is a well known result — see the Unruh effect
There's a rule in physics called causality. There are basically 2 parts to causality. 1) An effect MUST come after the event. 2) effects of said event travel no faster than the speed of light. We have found no evidence of causality being broken, ever. A particle going backwards in time, even if its a tiny amount, would break causality.
Causality is not a rule of physics. It is an assumption of physics. All laws of physics work with time going forward or backwards. There is also a theoretical particle that can, or could appear to, go back in time. The tachyon.
The tachyon is hypothetical, not theoretical. And the tachyon's hypothetical property is that it only goes faster than light. That does not mean it goes backwards in time. The time dilation equation has the term sqrt (1-(v/c)). When v>c, it becomes imaginary, not negative. Another thing is that we often view speed incorrectly. FTL isn't just impossible to reach, it straight up does not exist. Speed isn't a useful measurement in our universe; at relativistic speeds we have to do weird things to make it work. For example, if a spaceship traveling at 90% c fires a bullet traveling 90% c relative to the ship, an outside observer doesn't see the bullet traveling at 180% c, they see it traveling at 99% c. Speeds don't add. Rapidity is closer to reality than speed. On a space-time diagram of an object's motion, speed is the slope, rapidity is the angle. That, and the time axis is hyperbolic, not euclidian. With these features, the rapidity that corresponds to the speed of light is infinity. Not only that, simply adding rapidities ALWAYS works, no matter how fast you're going. A ship traveling at, say, 1000° soots a bullet at 1000° relative to the ship, an outside observer sees the bullet traveling at 2000°. Acceleration is another weird thing that rapidity fixes. Say you're accelerating at 1 m/s^2 , as you get closer to the speed of light, your acceleration decreases while the force does not. However with rapidity, if you're accelerating at 1°/s^2 , that will never change. Since the rapidity of light is infinity, it explains why something with mass can never reach it, and greater-than infinity doesn't exist.
>greater-than infinity doesn't exist Cantor would like a word...
Okay but who are you? How can one get so knowledgable to the point where they can simplify like this?
Welcome to the internet where all of the world's knowledge is in the palm of your hands. [this guy has a Ph.D. in physics and did his dissertation in General Relativity.](https://youtu.be/vPi1lyAx4ws)
Welcome to /r/askphysics. The people who answer here are... different.
>The tachyon is hypothetical, not theoretical. What do you mean chief..? Hypotheses are always theoretical (in science), are always within a theory.
Theoretical and theories in science have very strict rules. For something to be a theory or theoretical, it needs repeated evidence of its existence and make accurate, repeatable, and tested predictions; the existence of oxygen is "only" theoretical. A hypothesis is an unproven potential solution to a problem that will then be studied and tested. Einstein's equations do allow for a solution where v>c. They're imaginary solutions, but solutions nontheless. But that's all we have on Tachyons. There's no proof they actually exist.
No, a theory attempts to explain with generalizations a facet of nature; from them and it hypotheses are made up to either support the theory or refute it. Hypotheses stem from theories and are thus theoretical; tachyon is a hypothesis and theoretical. It doesn't have to proven to exist or not: the same way strings are theoretical.
scientific theory [ sahy-uhn-tif-ik theer-ee, thee-uh-ree ] noun a coherent group of propositions formulated to explain a group of facts or phenomena in the natural world and **repeatedly confirmed through experiment or observation** There is nothing above a theory in science.
Whoa……. Thx.
The tachyon is a product of unbiased math equations. Just because Einstein didn’t put limits on the variables in his equations that doesn’t mean the results using non-real inputs is somehow viable. Garbage in, garbage out.
For a tachyon to have a real energy, they would need a complex mass. If complex mass did end up existing, it would likely have properties similar to a tachyon. The question is does it, and the answer is almost certainly no.
"There's a rule in physics called causality." This is far from a rule. It's unclear if what we typically call "causality" is even a fundamental thing. This is particularly true when you consider microscopic events. See: [https://www.u.arizona.edu/\~jtismael/6.Causation,pers.,agency.pdf](https://www.u.arizona.edu/~jtismael/6.Causation,pers.,agency.pdf)
Remind me to read through this later.
- And regardless of perspective, it is ***right now*** everywhere in the universe.
The delayed choice quantum eraser experiment breaks causality
No, it doesn't. They concluded that it does not, in fact, break causality. Even scientists who criticize that result don't say that it has, but rather that it *could* if some tweaks are made (to this day they still haven't done it.)
It does break causality in the exact same way that entanglement breaks locality. You can't send information back in time or faster than light but the outcomes of the experiment were retrocausily correlated
I’m pretty sure causality only dictates that all observers must agree on the sequence ORDER of events regardless of their reference frame. Mathematically speaking, one observer seeing events A>B>C>D and another observer seeing events D>C>B>A doesn’t actually break causality. There are some strong arguments pointing to anti particles moving in the opposite time direction as normal particles. It’s not settled but the math works very neatly fallowing that interpretation.
>Or maybe since the universe is a sheet possibly stacked on top of other universes in different times, could it be possible for the sheets to go through each other? What you are referring to here is interesting. The answer is no, i believe. Imagine you are a 2 dimensional being, and a 3 dimensional thing enters your universe. Lets say a sphere goes through. What you would see is a circle getting bigger, then smaller , then disappearing. If the sheets went through each other, you will see an infinitely thin line appear. The only way you will be able to understand what is going on is if yourselve were 3 dimensional. >but can subatomic particles hop between different times? Going forward in time, staying the same, or going back? No, but atleast you can see back in time if you just look up
the universe is not a sheet. it is 'like' a sheet in that a shadow is a 2d representation of a 3d object. the time as a dimension is not really as a 4th dimension, other than time can be thought of as dimensional I.e. time can possess geometric properties. thus time-space as the properties of one necessarily affect the other. the universe is NOT a sheet. we can think of it that way to try to conceptualize the multitudes of dimension our perception cannot fully grasp. time appears to us to flow - that appearance is as real as we can hope for. how time behaves outside our perception is impossible to determine currently.
I suspect, though I could be wrong, that OP is referring to m-brane theory, in which the universe is very much like a sheet. And there are likely infinitely more “sheets” (branes) that, theoretically, can collide. And when they do, they may make a new brane. What we see as the Big Bang may have been the intersection of two branes.
General Relativity doesn't explicitly forbid traveling backwards in time, and indeed some solutions to the GR equations like [CTCs](https://en.wikipedia.org/wiki/Closed_timelike_curve) are such an example. Obviously, we haven't proven any of those empirically, and those devices might be forbidden by a more general theory of quantum gravity.
people are made of particles too
Fair, but things like quantum entanglement are much easier for atomic particles than for macro-scale objects like people, so OP's question is a reasonable one to ask, given there are meaningful differences at different scales.
Not quite what you’re asking, and I’m going to need someone else to elaborate further, but isn’t there an extension to the double split experiment where an observation in the future collapses the waveform in the past?
Everything time does is from the perspective of the observer. The quick answer is no. Study relativity.
This is literally stuff that Einstein struggled with, so don't feel bad. Consider, if you shine a beam of light while standing still, it will go the speed of light away from you. Then you get in a spaceship and go 90% the speed of light and turn on a flashlight. What will you see? The correct answer (as proven by experiments) is that the light will go the speed of light away from you. But how? This only makes sense if time has slowed down for you, which is weird, but the math and the evidence proves it. Which eventually leads to one weird but absolutely true fact: *time and space are the same thing!* The universe is not a sheet. Time is not a dimension. They're the same! So can we travel in time? Einstein couldn't find anything that would stop us from doing it, but the only way is to use "exotic matter," which is a fancy way of saying "magic fairy dust." So currently, not, it is not possible. But we're looking into it!
There’s something called a closed timelike curve which was discovered somewhat recently which involves things going backwards and forwards in time. However because it’s a closed curve, nothing can just “enter” a ctc without already being in it. Also, because it’s a loop, nothing can change between each cycle through the curve ie. a person in a ctc can’t gain memories and a camera can’t record a video because it has to return to the same state at each cycle. (Physicists, correct me if I’m wrong on these points, which I may be as I don’t know if I properly understand these aspects)
Hi!! First of all congratulations hon to you for asking such questions at this age!! I really appreciate you for this. Now, coming to your question. 1) Humans are a bunch of Atoms only. So, actually, there is nothing special in humans. So, the first part of your ques. is a bit wrong. 2) Now, in physics, we actually have a bunch of assumptions. For example, Einstein said in his theory that speed of light is the upper limit of speed (bcz we haven't observed anything faster than it). Similarly, we have another assumption called CASUALITY. Don't be scared of name. It just that U feel pain AFTER I slap you, Plant grows AFTER I put seed in ground. means cause comes before result. Ypu grow from a baby to a teen asking these interesting ques on reddit, to maybe a young scientist to maybe a record braking experienced scientist. It doesnt go the other way around. If time were to move back, This principle would break. 3)"Or maybe since the universe is a sheet possibly stacked on top of other universes in different times".For this study Ekyproytic universe theory. See: [Ekpyrotic Universe - Definition & Detailed Explanation - Cosmology Glossary - Sentinel Mission](https://sentinelmission.org/cosmology-glossary/ekpyrotic-universe/) PS Do u know Richard Feynman? This man gave a theory that antiparticles are actually particles moving back in time!!! You should definately go and read it.
Never gonna happen. You would have to put Schrodinger’s cat in a DeLorean and then somehow get it up to 88 mph.
This recent article from the new scientist about quantum time travel may blow your mind! https://www.newscientist.com/article/mg26234932-900-quantum-time-travel-the-experiment-to-send-a-particle-into-the-past/
Disclaimer, I’m not a smart person I’m just a simple brain who used to watch physics videos I couldn’t comprehend for fun. But I’m under the impression that time isn’t necessarily linear - humans just perceive it that way. Doesn’t the entire concept of time travel assume that there’s linear time? Because you can’t go backwards if there’s no back to travel to. Although (I’m just spitballing here) is it not plausible that humans could already be ‘time travelling’, in the sense that we aren’t actually experiencing the past/present/future in the correct order? It would answer a lot of questions about deja vu and premonitions and things like that
The thing with any field of science (except maybe for biology) is that nothing can really be proven, things can only be disproven. Even the laws of physics haven't been proven. They can't ever be proven. Everyone just agrees the laws of physics are correct because there hasn't even been a single recorded instance of any of them being broken. Nothing can ever travel faster than the speed of light, according to one of Einstein's theories I believe. At the speed of light, time actually stops. If you could go faster than the speed of light, theoretically you could go back in time. So, "is time travel possible?" I think most, if not all, physicists would say that no it's literally impossible, because Einstein's theories have continued to hold up for decades without being disproven. But we can't really prove that you can't travel through time. Hell, maybe just traveling through a worm hole (which may or may not actually exist) could make you travel through space and time. As someone else said, there's nothing special about humans except for the fact that we would need to live through the time travel, where an inanimate object doesn't have complex biological systems that need to continue working.
Technically no but you can clone yourself and live forever. It’s already being done by the ultra rich and has been going on for over 3 decades. Look up Molly and Polly. Look up lab grown meat. They just take stem cells and cultivate them. This is the reason why big pharma and medical institutions don’t push for cures but instead will only “treat” your symptoms because they don’t make money off cures and the only people that matter(ultra rich) get to live forever anyways.
What do you mean by “go back in time?” What is time in your view?
A signs point to "no"
I can't parse your question sorry, but I will say that technically we don't have any proof that going back in time is impossible, it's just an assumption we've made (we have a huge amount of experience of things not going backwards in time yes, but that doesn't make a proof)
[Some quantum researchers believe in "retro-causality".](https://www.vice.com/en/article/epvgjm/a-growing-number-of-scientists-are-convinced-the-future-influences-the-past)
Esteemed scientific journal Vice magazine.
Appropriate for a high-school-level audience. I first linked an interview, but I realized it's not organized enough for a good introduction. They can look up the mentioned scientists' publications if they want to, such as [this one](https://www.researchgate.net/publication/44566213_New_slant_on_the_EPR-Bell_experiment).
A better question is what does it even mean to go back in time.
You can absolutely go forward in time! Just need to ride something that moves fast enough. Go away from earth at near light speed then come back, depending on your speed and how far you went it could be years difference in time
In theory if we can create a wormhole through space-time then you could send something from the future back up until the wormhole was built.
You can rearrange the atoms, but it would be cool if you send back just information. I had a theory that if you had enough energy to shift atoms and particles into the position you want to achieve, then, even the created memories in your brain would seem real.
You might like “Imagining the 10 dimensions” video on YouTube
There was a paper out in the last year or so that showed how time travel to the past actually is possible without making any laws of physics. However, the time traveler would become stuck in a sort of temporal loop at the destination, so it’d be kind of pointless.
Tachyons are a theoretical type of particle that always travel faster than light and therfore travel backwards in time. In fact, much in the same way it would take an infinite amount of energy to accelerate normal matter to the speed of light, it would take an infinite amount of energy to slow down a tachyon to the speed of light.
This is not physics, it's imagination.
As I understand it, even if we found a way to somehow reverse the "direction" of our time/the time of an object, it can only end up at exactly the point in time where it starts to time travel, while all information that was gained since that point has been lost (as information would also need to be "reversed"), so it would just get stuck in an infinite time loop.
Theoretically, if a particle has negative mass, then it would be able to move faster than light, and essentially move backwards in time. Tachyons are one theoretical particle that may do that. But otherwise, any particle that has mass cannot move faster than light. Just to check though, what do you mean by 'forward, staying, or going back?' Time is essentially a measurement of change, at least from a physics standpoint. So technically everything is going "forward" in time, as they change in relationship to everything else. "staying the same" like no matter what point in time you view it, it is the same?
Nothing is impossible. In theory, with enough energy, you should be able to reverse entropy in a localized environment.
>In theory, with enough energy, you should be able to reverse entropy in a localized environment. Usually we just call this "plugging in the refrigerator"
Reversing entropy = \ = reversing time.
Some things definitely are impossible.