# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Kryptid on 01/04/2016 20:37:36

Title: How can I solve this relativity "contradiction"?
Post by: Kryptid on 01/04/2016 20:37:36
I'm currently in a debate with someone who is a relativity denialist. He posted this thought experiment in an attempt to "prove" that time dilation cannot exist:

I think the solution to this "contradiction" lies in the relativity of simultaneity (that is, one ship will see itself as arriving at point C before it sees the other arrive). However, I've come to another problem: what does the signal coming from ship B look like from the perspective of ship A? We know that the signal from ship B must be intercepted by both point C and by ship A in all reference frames because you cannot have reference frames with potentially contradictory causal results (i.e. the ship might be programmed to explode upon receiving the signal, and if it receives the signal in one frame but not another, we have a causal contradiction). Will ship A see ship B send the signal before ship B arrives at point C? Any mathematical help would be nice too.
Title: Re: How can I solve this relativity "contradiction"?
Post by: RD on 01/04/2016 22:31:55
"The precise point they pass by C" will depend on how fast the rocket is travelling : if close to the speed of light there will be visual distortion, see ... https://www.youtube.com/watch?v=gTqqD5N3EbM (https://www.youtube.com/watch?v=gTqqD5N3EbM)
https://youtu.be/9lMYhhCkPXE?t=35s (https://youtu.be/9lMYhhCkPXE?t=35s)

The apparent bearing of C as seen from a rocket will change depending on the rocket's speed.
Title: Re: How can I solve this relativity "contradiction"?
Post by: Kryptid on 01/04/2016 23:15:50
That first video is interesting. Of the squares in a single "plane", those closer to us seem to pass by us before those that are further from us. Is that a visual illusion or is space really distorted in that manner at such speeds? The distance that an object is from us affects how it will distort?
Title: Re: How can I solve this relativity "contradiction"?
Post by: jeffreyH on 01/04/2016 23:28:12
I'm currently in a debate with someone who is a relativity denialist. He posted this thought experiment in an attempt to "prove" that time dilation cannot exist:

I think the solution to this "contradiction" lies in the relativity of simultaneity (that is, one ship will see itself as arriving at point C before it sees the other arrive). However, I've come to another problem: what does the signal coming from ship B look like from the perspective of ship A? We know that the signal from ship B must be intercepted by both point C and by ship A in all reference frames because you cannot have reference frames with potentially contradictory causal results (i.e. the ship might be programmed to explode upon receiving the signal, and if it receives the signal in one frame but not another, we have a causal contradiction). Will ship A see ship B send the signal before ship B arrives at point C? Any mathematical help would be nice too.

Title: Re: How can I solve this relativity "contradiction"?
Post by: alancalverd on 02/04/2016 00:11:59
Ask your denialist why the experimental evidence matches the predictions of relativity.
Title: Re: How can I solve this relativity "contradiction"?
Post by: Kryptid on 02/04/2016 20:12:54
I'm currently in a debate with someone who is a relativity denialist. He posted this thought experiment in an attempt to "prove" that time dilation cannot exist:

I think the solution to this "contradiction" lies in the relativity of simultaneity (that is, one ship will see itself as arriving at point C before it sees the other arrive). However, I've come to another problem: what does the signal coming from ship B look like from the perspective of ship A? We know that the signal from ship B must be intercepted by both point C and by ship A in all reference frames because you cannot have reference frames with potentially contradictory causal results (i.e. the ship might be programmed to explode upon receiving the signal, and if it receives the signal in one frame but not another, we have a causal contradiction). Will ship A see ship B send the signal before ship B arrives at point C? Any mathematical help would be nice too.

I think he believes that, since both ships receive a signal from each other at the same time with no delay, that ship A could not see ship B as have dilated time relative to itself (and vice versa). I countered that there would indeed be a delay because both ships will not arrive at point C at the same time in their own reference frames.
Title: Re: How can I solve this relativity "contradiction"?
Post by: hamdani yusuf on 07/04/2016 07:23:03
I think he believes that, since both ships receive a signal from each other at the same time with no delay, that ship A could not see ship B as have dilated time relative to itself (and vice versa). I countered that there would indeed be a delay because both ships will not arrive at point C at the same time in their own reference frames.
If we take A as reference point, where is B when ship A arrives at point C?
Title: Re: How can I solve this relativity "contradiction"?
Post by: hamdani yusuf on 07/04/2016 13:00:39
Or rather,
If we take A as reference point, where is B when ship A is just start moving?
Title: Re: How can I solve this relativity "contradiction"?
Post by: puppypower on 07/04/2016 13:15:10
The easiest way to look at time dilation is in terms of an energy balance; energy conservation, and not in terms of relative reference.

For example, in the twin paradox, only the moving twin ages slower. It is does not matter if the stationary twin pretends he is the twin in relative motion. It is all about who has the actual energy; energy conservation. Only the moving twin had actual energy, added as rocket fuel, for propulsion. Therefore only that twin will show any tangible time dilation. The stationary twin does not age because his energy never changes based on energy conservation.

As a useful analogy, consider the relative reference workout. In this weight loss workout, you sit in the middle of a running track and watch the runners run around the track. In this workout, all you do is pretend you have relative motion. This allows you to burn calories and lose weight while sitting. Most people can intuitively sense this will not work, because energy conservation will trump relative motion. The burning of calories; time dilation, cannot occur unless there is an actual energy expenditure; conservation of energy.

In your example above, if both rockets are the same and used equal energy and move at the same velocity, they both will show the same time dilation everywhere along their flights. The time delay for signals from each ship to reach each other is not relevant to their energy balance. The signal between tends to confuse the issue.

Note:

Kinetic energy is 1/2MV2. Kinetic energy will square the velocity. The squaring of velocity has the impact of normalizing the vector; direction of the velocity. It does not matter if the object is coming or going, since the kinetic energy is only dependent on the scalar of velocity and not the vector. There will be as much time dilation in an expanding or contracting universe, if both have the same velocity.

On the other hand, from earth, an expansion scenario will show a red shift while a contraction scenario will show a blue shift. This will alter the apparent energy balance of the universe, even though there is a constant time dilation. The confusion is a connected to the earth being used the zero state of energy; relative reference workout.
Title: Re: How can I solve this relativity "contradiction"?
Post by: yor_on on 23/03/2018 21:18:54
I know. A old thread, but Kryptid, where is the proposition he made?
How did he express this thought experiment and his conclusion?

Title: Re: How can I solve this relativity "contradiction"?
Post by: Kryptid on 23/03/2018 22:27:15
I know. A old thread, but Kryptid, where is the proposition he made?
How did he express this thought experiment and his conclusion?

I've long since taken the image off of my Photobucket account. I haven't been back to that website in over a year, so I've practically forgotten what his argument was about.