# B Relativity problem

1. Aug 11, 2016

### alan_longor

hello .

-so if a magical spaceship flies from earth at 80% the speed of light . time should go slower for the person inside the spaceship due to time dilation . so time goes slower for him . the thing is if we change the way we look at it and reverse it . aren't we moving away from the spaceship at 80% the speed of light to ?

-why does time have a rate ? so time has a current rate , if we move it slows down . what get the first rate to exist in the first place ?

-if humans do not exist and no intelligent being exists , nothing that can have a notion of time exists .
does time itself exist then ?

-if i have two tennis balls , and i throw one and let go of the other . one of them should fall down while the other goes up . now if we stop the flow time , they will both be still in place though if time runs again one of them will go up and the other will go down , what's the physical difference in space that get's one to go up and the other to fall ? is the information about movement stored inside the 3 dimensional space ?
if you know everything about the 3 dimensional space at a given time , can you tell what happens next in time ?

-is the information that describes reality changing ? or is it constant and well determined ? .
i mean , i know that we are going through time and things are changing . but you take one time frame with one 3 dimensional space .. isn't the third dimension the time axis of the second dimension ? though we see space in that exact time frame as something well determined and fixed . and if a 4th dimensional creature looks at us and our time he will see everything that ever happened but it will be stable and fixed in one 4 dimensional frame . and you can keep going up in dimensions and the same observation keeps happening . so how can we know ?

Last edited: Aug 11, 2016
2. Aug 11, 2016

### BvU

No. (That isn't a question, it is a supposition - and incorrect). Time passes at one second per second for the traveller, so it does not go slower to him. But if the persons that remain on earth look at the traveller's watch, they see it advance at a slower rate (0.6 seconds on the traveller's watch per second on their own watch in your example). There is asymmetry: the traveller is the only one who accelerates.
dunno
yes

Two tennis balls -- they both accelerate towards the earth. Gravitation. There's no difference in space, only in initial conditions.
Classical answer: yes. Equations of motion and such. More modern answer: no. Why not ? Because you can't know everything you need accurately enough. Fundamentally, due to the uncertainty relationships.

Caveat: this is a 'layman's answer' -- I'm curious to find out what the real experts have to say!

3. Aug 11, 2016

### hsdrop

that's like asking if a tree falls in the woods with no one around does it make a noise in short i believe it does it's also like asking if no one was around for the big bang did it happen and again yes i believe it did scientist and philosophers have been going round and round for ages with this same question in my point of view it a little bit self centered to think that something didn't happen if someone didn't see it

also i think there is a forum just for "relativity and special relativity"

4. Aug 11, 2016

### Staff: Mentor

Yes, we can either consider the earth to be at rest while the spaceship is moving at .8c, or we can consider the spaceship to be at rest while the earth is moving in the opposite direction at .8c; both descriptions are equally valid and consistent.

Either way both observers will find that their clock, which is at rest relative to them, is running normally while the other clock, which is moving relative to them, is time-dilated by a factor of .6. That is, both observers will correctly conclude that the other clock is running slow. This appears to be a contradiction (how can A be slower than B and B be slower than A?), but in fact it makes sense if you also consider the relativity of simultaneity - there are many posts explaining this already.

5. Aug 11, 2016

### girmv112358

I'm not sure time is real. I think relative motion is time. Because motion occurs at relative rates we say it occurs in time, but then why is time traveling into the past an impossible paradox while traveling forward is perfectly reasonable? Motion can't be altered after it occurs. Time dilation can be described perfectly as motion in certain directions slowing down or speeding up. Time doesn't slow down in a space ship traveling near c, the hands on the clock would simply defy physics if they maintained their usual earth speed while also moving in one direction much faster. The Pythagorean theorem can prove that

6. Aug 11, 2016

### Stephanus

Perhaps I can answer it not through quotation.

hello .

Ok

-so if a magical spaceship flies from earth at 80% the speed of light . time should go slower for the person inside the spaceship due to time dilation .
No, that is wrong!. Time for a person inside the spaceship still ticks at the same rate, whatever it is. Perhaps your question should be.
Time for a person outside the spaceship which is not comoving with the ship will look slower.
I think this needs a further explanation.

so time goes slower for him . the thing is if we change the way we look at it and reverse it . aren't we moving away from the spaceship at 80% the speed of light to ?
Yes! We are moving away from the spaceship at 80% the speed of light.

-why does time have a rate ? so time has a current rate , if we move it slows down . what get the first rate to exist in the first place ?
-if humans do not exist and no intelligent being exists , nothing that can have a notion of time exists .
does time itself exist then ?

I think @hsdrop 's answer is right
Perhaps what you meant was, if all matters in the universe are vanished into energy or the universe becomes heat death, does time itself exist? But I think that belongs to cosmology?
Again @hsdrop is right.
-if i have two tennis balls , and i throw one and let go of the other . one of them should fall down while the other goes up . now if we stop the flow time , they will both be still in place though if time runs again one of them will go up and the other will go down , what's the physical difference in space that get's one to go up and the other to fall ?
Now, this is a tricky question. You stop the flow of time...
For whom/what. You and the earth? Or you and the earth and the whole universe?
If you look at a spaceship that travels almost at the speed of light, you'll see that its time slows down or almost stop or if you look and object before it enters the event horizon, you'll see that time for the object will slow down.
But to stop time in a closed system? What about all the trillions of atom in that system? What about the state of the electrons in that system? If somehow you manage to stop the time in a closed system and all the electron stop, it will be in absolute zero temperature, or that system might not be in our universe anymore. I can't answer further, it will be a speculation. The only region where time stop is inside an event horizon. And scientist concluded that everything inside the event horizon is not part of our universe.
To name a few.

is the information about movement stored inside the 3 dimensional space ?
The same answer goes. I don't know it's speculation I think.

if you know everything about the 3 dimensional space at a given time , can you tell what happens next in time ?
Now, I think it is quantum mechanic predeterminism? While there are some aspect as Heisenberg Uncertainity involded, I can't answer further.

-is the information that describes reality changing ? or is it constant and well determined ? .
i mean , i know that we are going through time and things are changing . but you take one time frame with one 3 dimensional space .. isn't the third dimension the time axis of the second dimension ? though we see space in that exact time frame as something well determined and fixed . and if a 4th dimensional creature looks at us and our time he will see everything that ever happened but it will be stable and fixed in one 4 dimensional frame . and you can keep going up in dimensions and the same observation keeps happening . so how can we know ?

I wonder, nobody haven't answered this

7. Aug 11, 2016

### Staff: Mentor

This is too vague to even give a basis for discussion.

Have you actually worked out, mathematically, how a rapidly moving clock's hands would appear to move? Or, to take an easier case, have you worked out how a light clock--a clock composed of two mirrors with a beam of light bouncing back and forth between them--would appear to someone relative to whom it was moving rapidly? Start with the case of a light clock moving rapidly in a direction perpendicular to that in which the beam of light bounces. Remember to include the fact that the light itself moves at c relative to all observers.

8. Aug 11, 2016

### alan_longor

thank you very much .