Exploring the Concept of Time Traveling

[Azrion]

I am curious about time traveling.

According to Einstein's special relativity, the easiest way to travel into the future is by approaching the speed of light or faster.

Now assume this setup:

• Sunlight travels to Earth at c (speed of light).
• We have the technology to reach speeds faster than c with a spaceship.

If Person A travels from Earth to sun, back and forth (infinitely), the light coming from the sun slows down (for Person A) since A travels faster than c. Let's say Person A travels much faster than c. Wouldn't the light from the sun take forever to reach Earth (from the perspective of Person A)? Thus, how can Person A travel into the future if A needs to wait longer until the light reaches earth? Wouldn't Person A inside the spaceship get older and older while nothing has changed on Earth for Person B?

Did I misunderstand the concept?

 

[lomidrevo]

We have the technology to reach speeds faster than c with a spaceship.

Here is where your "concept" breaks down, as it is impossible for massive particles to travel at the speed of light or faster.

 

[Ibix]

We have the technology to reach speeds faster than c with a spaceship.

This is impossible in a universe governed by relativity. We cannot answer your question using relativity because it is analogous to asking "if up were down, how would we move up without moving down?" - i.e., it's self-contradictory. And we have no other theory that let's you describe someone traveling faster than light, so we cannot answer your question on any other basis either.

light coming from the sun slows down

This is not correct. A fundamental premise of the theory of relativity is that the speed of light is always the same for all inertial observers. That, incidentally, is why you can't describe someone moving at or above the speed of light, since you can't have light always overtaking you if you are traveling at or above its speed.

 

[PeroK]

According to Einstein's special relativity, the easiest way to travel into the future is by approaching the speed of light or faster.

The easiest way to travel into the future is just to wait. The future will come soon enough.

Did I misunderstand the concept?

Yes.

 

[Azrion]

I was interested in the idea of how people assume that we are traveling into the future when reaching speed of light. I know that it is impossible to reach speed of light with a spaceship. However, I want to know what makes people think that we may end up traveling into the future and not otherwise? Thus, I gave a example to picture an unrealistic scenario.

 

[PeroK]

I was interested in the idea of how people assume that we are traveling into the future when reaching speed of light. I know that it is impossible to reach speed of light with a spaceship. However, I want to know what makes people think that we may end up traveling into the future and not otherwise? Thus, I gave a example to picture an unrealistic scenario.

As far as I'm aware, you're the only person who thinks this! Who are these other people?

 

[lomidrevo]

It doesn't make any sense to ask this question within the special relativity framework (nor any other currently accepted mainstream theory), $c$ is the limit.

 

[Azrion]

As far as I'm aware, you're the only person who thinks this! Who are these other people?

Since I am a kid we always hear it. In documentaries or web articles.
Here is a quote I quickly googled (from cosmosmagazine.com):

Speed. This is the easiest and most practical way to get to the far future – go really fast. According to Einstein's theory of special relativity, when you travel at speeds approaching the speed of light, time slows down for you relative to the outside world

I like to see an example of what they claim.

 

[PeroK]

I like to see an example of what they claim.

There is time dilation; and there is differential ageing.

What's possible is for two people to start at the same point in spacetime (place and time), take different paths through spacetime and meet up at the same point in spacetime and find that more time has passed for one than the other. This is called differential ageing and is a simple consequence of spacetime geometry.

The simplest example is called the twin paradox. You'll find about a hundred threads on here about that.

 

[Azrion]

This is called differential ageing and is a simple consequence of spacetime geometry.

Since this is a consequence of spacetime geometry, we can't really talk about time traveling here (at least what the mainstream thinks it is).

So we can conclude that time traveling is impossible simply by reaching speed of light(?)
Especially, when taken the same path where differential ageing has no effects on it.

I feel betrayed by media

 

[PeterDonis]

Here is a quote I quickly googled (from cosmosmagazine.com)

That quote does not say "move at the speed of light", much less "move faster than the speed of light". It only says "speeds approaching the speed of light". The scenario you posed in your OP has nothing whatever to do with what the quote you gave is saying.

I like to see an example of what they claim.

Sure, any "twin paradox" scenario will do. For example, suppose you have a spaceship that can travel at 87% of the speed of light. The time dilation factor for that speed is 2. So say you travel to Alpha Centauri and back in your spaceship; for simplicity we'll say the journey is 4 light years (in an assumed frame in which both Earth and Alpha Centauri are at rest) each way. According to Earth clocks, it will take you about 9.2 years to make the trip. But according to your clocks, on your ship, it will take only half that long, about 4.6 years. So when you get back, you will have aged only 4.6 years, but you will be 9.2 years into the future of the Earth that you left.

The closer your speed gets to the speed of light, the bigger the time dilation factor. For example, suppose your spaceship could travel at 99.99999999% of the speed of light. The time dilation factor for that speed is about 60,000. So you could travel to the center of the galaxy and back, about 30,000 light-years each way, in just 1 year by your clock. You would age only 1 year during the trip, but when you got back, you would be 60,000 years into the future of the Earth that you left.

 

[Nugatory]

Here is a quote I quickly googled (from cosmosmagazine.com):

Stuff luke this is the reason why this forum has its rule requiring that sources be serious textbooks or peer-reviewed and published scientific papers.

If you are genuinely interested in relativity, you will want to get hold of a proper textbook and learn the real thing instead of depenidng on random drivel flowing around the internet. I personally am partial to Taylor and Wheeler's "Spacetime Physics", and other members here will have ther suggestions for good books at various levels.

 

[lomidrevo]

I remember one episode in Sean Carroll's podcast, talking about time travel, so maybe you would be inrested to hear that:
https://www.preposterousuniverse.co...4-solo-how-time-travel-could-and-should-work/

However, note that he discuss not only scientific point of view, but also viewpoint of an advisor for sci-fi movies. So be careful
I haven't listened all this episode, maybe just the first half, so I don't know all the content, but he covers some interesting insights from SR, GR and QM.

 

[PeroK]

I personally am partial to Taylor and Wheeler's "Spacetime Physics", and other members here will have ther suggestions for good books at various levels ...

... The first chapter of Morin's book is free online here:

https://scholar.harvard.edu/files/david-morin/files/relativity_chap_1.pdf

 

[PeterDonis]

It's total nonsense

I don't think that's accurate as far as the specific quote given (although it might be a fair description of the article as a whole; I don't know since I haven't read it). In post #11 I gave examples of what I think the specific quote given was describing.

I agree that the source given is not a valid source for PF discussion and a relativity textbook would be a much better place to learn what relativity says.

 

[Nugatory]

I don't think that's accurate as far as the specific quote given (although it might be a fair description of the article as a whole; I don't know since I haven't read it). In post #11 I gave examples of what I think the specific quote given was describing.

I agree that the source given is not a valid source for PF discussion and a relativity textbook would be a much better place to learn what relativity says.

Yep - I edited that part out after I saw that it didn't clearly say what was claimed. Advice about not learning from th einternet is still good, I think

 

[phinds]

I feel betrayed by media

As well you should. We have MANY threads here on PF that have been started by people who, like you, have been completely misled by pop-science presentations. Remember, such presentations are entertainment, NOT education.

 

[vanhees71]

Yep - I edited that part out after I saw that it didn't clearly say what was claimed. Advice about not learning from th einternet is still good, I think

Well, it's at least very strangely worded. What does it mean to say "travelling into the future". Isn't that what everything does "all the time", no matter whether you discuss relativistic or Newtonian physics? And what does it have to do with moving at speeds close to $c$ within relativistic physics? First of all you have to tell, which reference frame you are using to say something has a "high speed". Is there anything more fundamental to relativity than the conclusion that Leibniz was right after all in saying that there's no absolute space nor absolute time but all motion is relative?

I'd also say the above quote from this website is pretty much nonsense. Nowadays with the WWW it's not the problem to get information about anything you like. The problem is to figure out, whether it's serious science-based information or not. The lesson to be learned from this example is that you have to be very critical against any information. Using textbooks from a good scientific publisher is already a pretty good approach to be quite sure to get correct scientific information. I'd consider peer-reviewed original scientific papers from trustworthy publishers the most safe option.

Even there you have to be critical. This Summer when rewriting the introductory part for my quantum mechanics lecture notes I started to think a bit more about the photoeffect and the classic measurement using Millikan's method of the stopping potential. While of course the determination of $h$ is everywhere correct, while almost all textbooks present the constant contribution $\Phi$ in the formula
$$U_{\text{stop}}=h \nu - \Phi$$
wrong. It's not the "work function" of the cathode (emitting electrode) but that the anode (collector electrode). They forget the contact potential when connecting the cathode and anode, which may be (and in the original experiments by Millikan in fact have been) made of different materials. BTW: Millikan got it right and also verified this in a long series of careful experiments (with the big struggle with electrodes changing by oxidation, leading to different values for $\Phi$ when repeating an experiment even with the same apparatus). That almost all textbooks are wrong is well-known for decades (even from the very beginning of the discussed experiment), but usually textbook writers copy from each other, particularly if it's about "such a simple issue".

 

[lomidrevo]

Nowadays with the WWW it's not the problem to get information about anything you like. The problem is to figure out, whether it's serious science-based information or not. The lesson to be learned from this example is that you have to be very critical against any information. Using textbooks from a good scientific publisher is already a pretty good approach to be quite sure to get correct scientific information.

As a layman, I totally agree :-) The most interesting physics that I have managed to learn surely comes from verified (or well-known) textbooks. When I have enough time and I try to focus on a particular subject, I also like to follow open lectures, which are usually provided for free by many prominent universities, like Stanford, MIT, Yale.. One needs to sacrifice quite lot of free time to go over that, which is not always easy to combine with job, kids, wife and other regular duties. But the award is much deeper understanding. (usually, but not always the case )
Years ago, when I was reading only pop-sci books or articles provided on news portals aimed for general public, I used to have a mess in my head , quite lot of misunderstanding about the real physics.
I still read those, from time to time, but I know that not everything what is written there can be taken seriously.

I'd consider peer-reviewed original scientific papers from trustworthy publishers the most safe option.

For laymen like me, this is probably not the most suitable source of information. Firstly, these papers are not typically accessible to general public - either behind paywall or academic subscription needed. Secondly, papers typically involve the latest progress in very specific research and are written by professionals for professionals. So usually it is a bit difficult (or at least very time consuming) for me to follow them. Therefore I better stay with combo of textbooks and lectures. For breakthroughs I mostly rely on popular version of the articles, newspapers + extra discussions and insights here on PF

 

[vanhees71]

Sure, it was just a hint to be careful with online sources though there are some pretty good ones. Wikipedia is pretty good, and I'd also trust online-lecture notes on web sites of universities (professors, lecturers) as much as textbooks. Since nowadays the publishers don't have a proper copyediting anymore but just print the LaTeX source files of the author there are as much typos in a textbook as there are in manuscripts provided directly by the lecturers ;-).