/sci/ - Science & Math

>>3593771

Alright. How about two satellites, both in low-earth orbit, making many circuits of the earth per day, and keeping the same relative orbital positions to each other. They're both the same distance from the center of gravity; they're both moving at the same speed around that center of gravity; but they *are* revolving around each other, from the perspective of the other, with respect to the fixed stars. Do they experience time dilation, relative to each other? Or do they keep the same time?

>>3593703

Nobody's responding, so I'll say what I think might be the rebuttal to this.

While movement and position are not absolute, direction is. (Or at least, mostly is. It might experience some bendiness in the presence of gravitational fields.) Therefore, rotational movement around the sun, keeping the same distance to the earth, would still be relative motion to the earth.

>>3593682
>In rotational motion, the edges are moving relative to the center. I think that's all he meant.

But how do you know you are? For all you know, the center of mass of the nearest fifty galactic superclusters could, by chance, happen to be residing currently in the middle of our sun, with everything in the nearest 500 megaparsecs revolving around that point, in which case the spaceship might actually be moving much slower than you could measure just from reference points alone.

There are no absolute reference points: only relative motion can be measured, or is relevant in physics. So, while the spacecraft might have a high relative velocity compared to Neptune or a distant star, it still would only have very low relative motion compared to the earth; and therefore there should not be significant time dilation.

>>3593655
>Here's a thing: time dilation isn't dependent on moving relative to another object. It's dependent on /moving/.

:S
But you CAN'T be moving, EXCEPT relative to something else. ALL motion is relative. No motion is absolute.

>>3593648
>Uhh... If it moved around the sun, it would also occasionally move towards as well as away from the earth.

I mean, it's so far away from the sun that, moving at near-lightspeed, it completes a circuit of the sun in one year, and thus is always the same distance from the earth. I didn't think to specify something like that, sorry.

>If you mean it flies around the earth: the answer is yes, there is time dilation.

:/
But it has zero velocity relative to the earth. It changes *direction* from the earth, relative to other objects, but not distance.

Ooh! Another question.

A spaceship is flying in a circle around the sun at near lightspeed. Does the astronaut in the spaceship still experience time dilation relative to the earth, or can he only experience time dilation if he is travelling towards or away from the earth?

>>3593565
>this statement is simply false. there is no such thing as a reference frame of light.

But it's only false because it's impossible to have a reference frame of light, because time wouldn't pass in it; all speed would be infinite. Hence, the statement is, at least for practical purposes, if not in technical truth, accurate.

>>3593563

Er, wait. His perception of time would be slowing down at the same rate his receipt of signals would; so while he's accelerating, he would NOT perceive time on earth slowing down. Would he?

And then when he stops accelerating, and is going at a constant speed, he should start receiving messages very slowly. Then when he starts decelerating, the messages start reaching him more quickly, though still not at normal speed. It's only once he's back at the same speed as earth that he starts receiving messages in realtime, but they're delayed.

Then when he turns around and starts heading back, the signals start reaching him really fast, and it's like time on earth is rapidly accelerating. When he arrives home, his grandchildren are older than him.

It makes sense. It's the Doppler effect, applied on relativistic scales and terms.

>>3593552

Alright. Next question.

As the astronaut's ship accelerates, signals from earth start reaching it at a slower rate, from the perspective of earth. But wouldn't, due to time dilation, the signals appear to start reaching the astronaut faster? The people on earth start receiving his replies at a slower rate; but shouldn't he be receiving theirs at a faster rate, relative to his own perception of time? The video said he would perceive the people on earth as slowing down.

>>3593520
>A deep understanding of WHY all this is makes any sense requires a lot of math and thinking, not to mention the observations that tell us this is what the universe is really like, and not just a neat idea. It comes down to the physics of the universe obeying a Lorentz transformation rather than a Galilean one.

That's not really the "why", though; that's the "how". Measuring just how much the clocks seem to dilate when perceived from different reference points, and all that. That's all quantification, but it's not qualification.

The qualification – the why – is a simple property statement: lightspeed is, relative to itself, infinite. It is impossible to get any closer to lightspeed than you're already going, even if you are constantly accelerating relative to some other point.

A question, though: if, for the spaceship, a 10-lightyear journey only lasts a week, and fuel is burned at the same rate throughout, do the people on earth, for whom the journey seems to last several years, perceive the spaceship's fuel consumption as dropping to a very low level once the spaceship is near lightspeed?

>>3593472
>Hmmmm.... I don't really understand what you're thinking, so we haven't really connected yet.

Okay. Let me describe a hypothetical experiment.

You have a spaceship. This spaceship has as much power as you want it to have. Not infinite, but as much as you could possibly care to equip it with. You're going to use this ship to try and accelerate as close to the speed of light as you can.

Onboard the spaceship, there is a device that shoots a ray of light, forward (in the direction of travel, away from the earth). In front of this device is another device, that detects the light hitting it, and tells you how long the light took to cross the distance between the two devices; in other words, the device measures the speed of light, relative to you, while you're travelling.

Now, you set off from earth, accelerating. Behind you, earth zips away, growing more and more distant, at a speed approaching the speed of light.

But, no matter how fast you go, your twin devices keep giving you the same reading for the speed of light. It's still faster than you by the same degree. You're not getting any closer to it. Therefore, it seems to be accelerating "with" you, counterintuitively.

Alright. I'm going to summarize the impression I'm getting from these videos. The videos are not stating this explicitly, which makes me worried that I might be fucking this up.

Lightspeed is the impossible speed. All speeds are equally infinitely less than lightspeed. If, for example, you were to choose the planet earth as your arbitrary absolute reference point, and start flying away from it, constantly accelerating, you would perceive that light almost seems to be accelerating "with" you, in that you're not getting any closer to its speed. However, due to length contraction (?), the earth appears to be accelerating away from you at an increasing velocity which slowly approaches the speed of light.

Am I completely off, here?

>>3593400

The question I'm asking, however, is why, when the person on the starship returns to the earth, all his grandhchildren are older than him. If he always perceived earth's clocks as moving slower than his, then there's no room for them to have suddenly sped up and resulted in the passage of many years during his absence.

>>3593384

Or does the difference only arise during acceleration and deceleration?

>>3593378

In other words, when the "mover" arrives at another planet, and contacts the "stander" on the original planet, more time would have elapsed for the "stander"; so the "stander's" clock would have HAD to have been moving faster.

OP here, I just paused at 6:17 in the second video.

Why does the person with the "moving" clock perceive the "still" clock as moving slower? Shouldn't he perceive the "still" clock as moving faster?

>>3593267
>Light is ALWAYS at c. It's time and space that are fuzzy.

The problem is that you're being vague. You're giving generals, when I'm looking for the specifics of a given scenario.

Take the scenario in the diagram in >>3593214. If the spacecraft is moving away from the planet at 0.1c, what exactly is the relationship between the passage of time in the two reference frames, that causes the light to be perceived in both as moving at exactly C?

>>3593242
>If your time moves slower, you perceive light as moving faster.

So... shouldn't the light relative to the spacecraft be perceived as moving 1.1c, or something?

>>3593204
>Because the frame of reference in which the planets are motionless and the frame of reference in which the spacecraft are motionless are different, and thus will experience different distances and durations.

Explain, then, the exact relationship between the two reference frames in the diagram in >>3593214, where the relative speed of the spacecraft from the planet is 0.1c. What about that relationship causes the light to appear to be moving at exactly C in both reference frames?

>>3593188
>What is that?

I am aware that there is no such thing as a real absolute reference point. That's why I specified that it's a "theoretical" absolute reference point; IE, a point that has been arbitrarily designated to be "absolute".

Here's a better and simpler diagram of my question.

>>3593189
>That's the entire point - the speed of light is the same in all inertial reference frames. You're just saying it doesn't make sense to you, which is perfectly understandable.

:(
I created this thread because I wanted someone to help me understand it.

>>3593170

But how? How can they be C relative to both the spacecraft and the green planet?

I do not understand relativity theory. Someone please explain this diagram to me.

Hello, /sci/. Today, I'd like to be educated.

I've been doing a lot of research lately but it's mostly tl;dr, so I'm asking you instead: How would neurotransmitters react to psychadelics (DMT, shrooms, LSD, salvia?, dextramethormphane, etc.) on someone who is about to have paranoia schizophrenia.

inb4 op should just do research
inb4 dextramethormphane and salvia are not psychadelics