Time Dilation Effects - Understand without Clocks

[mrSpring]

So I am having some hard time understanding exactly the effect of moving near light-speed on time. Most of the examples mention clocks as a way of measurement but I can understand why would a clock which is a mechanical or electrical device for measuring time would be effected with motion. That why I want to neglect the clock thing and get and a new measurement element

My question:

If I am on Earth and I am going to travel to a star which is one light year away from earth.
To survive for (one year) I drink exactly one tank of water every month so for one year trip I will need exactly 12 tanks of water
Now I got into my spaceship and successfully reached my final destination after a year of travel.

How many tanks did I consume?

12 as calculated or less?

Thank you very much

 

[Drakkith]

How fast were you going? You may or may not need more than 12 tanks. At 0.86c, time would pass about 50% the rate at which it does on Earth, putting your travel time (as measured by your water drinking) at just over half a year if my understanding is correct. Faster than that and you'd need less water, slower and you'd need more.

Most of the examples mention clocks as a way of measurement but I can understand why would a clock which is a mechanical or electrical device for measuring time would be effected with motion.

Everything is a clock. A block of uranium can be a clock by measuring the decay. A pulse of light can be a clock. The natural aging process can be a clock. The point is that the laws of physics don't differentiate between what we call clocks and everything else that we don't. Everything follows the same rules.

 

[Ibix]

If I am on Earth and I am going to travel to a star which is one light year away from earth.
To survive for (one year) I drink exactly one tank of water every month so for one year trip I will need exactly 12 tanks of water

This is a clock, closely related to the concept of a sand timer. A clock is simply a way to record elapsed time by counting a repeating process - your need to rehydrate yourself in this case. You can't measure time without a clock.

Now I got into my spaceship and successfully reached my final destination after a year of travel.

It is very important in relativity to be crystal clear about who is measuring what. The year of travel is measured by earthbound clocks, presumably. And presumably you are envisioning your ship traveling at 99.99% of light speed relative to Earth, so that the transit time is only very slightly more than a year.

The question is, then, how much time does the shipboard observer experience? The answer is much less than the earthbound observer - 3.65 days at the speed I suggested. So about 0.12 tanks of water used.

So I am having some hard time understanding exactly the effect of moving near light-speed on time.

I strongly recommend looking up the "block universe" and its more rigorous friend the Minkowski diagram. It isn't that motion affects time, so much as motion affects the natural choice of which direction in spacetime you want to call time. Clocks (including your water-clock) measure that direction so, if they are moving with respect to each other, measure different things.

 

[pervect]

You survive if your velocity (which you didn't specify) is greater than $\approx$ 70.7 percent of the speed of light, which algebraically is c dived by the square root of two.

At this velocity, it takes 1.414 years Earth time to travel one light year. But the time dilation factor is also 1.414, so it takes one year of ship time to reach your destination, and you'll drink your year's supply of water (12 tanks), arriving at your destination as you finish the last of your water.

If you fill up your water tanks when you arrive, then immediately come home, when you return home your brother, who stayed on Earth, will have aged 2.828 years, while you will have only aged 2 years.

 

[Janus]

Just to add to pervect's answer. For you, in ship the 1 light year distance as measured from the Earth will only be 0.707 light years when you have a 0.707 c speed relative to the Earth. This is because, by your measurement, it is the Earth and destination point that are moving at 0.707 relative to you, and the distance between them is length contracted. At 0.707c, it takes 1 yr to cover that distance.

As someone above has already alluded to, Relativity isn't about mechanical or electrical clocks being effected by motion, it is how inertial frame with relative motion with respect to each other measure time and space differently from each other.

 

[PeroK]

So I am having some hard time understanding exactly the effect of moving near light-speed on time. Most of the examples mention clocks as a way of measurement but I can understand why would a clock which is a mechanical or electrical device for measuring time would be effected with motion. That why I want to neglect the clock thing and get and a new measurement element

My question:

If I am on Earth and I am going to travel to a star which is one light year away from earth.
To survive for (one year) I drink exactly one tank of water every month so for one year trip I will need exactly 12 tanks of water
Now I got into my spaceship and successfully reached my final destination after a year of travel.

How many tanks did I consume?

12 as calculated or less?

Thank you very much

You have a fundamental misunderstanding here: motion is relative. The spaceship is traveling at near the speed of light relative to the Earth-Star reference frame. But, there is no physical experiment that will tell the spaceship that it has a specific absolute velocity. A clock on the spaceship is no more "in motion" that a clock "at rest" on the Earth.

Time dilation is symmetric. In the reference frame of the space ship, clocks (and water supplies) on Earth are dilated.

The asymmetry arises from the spaceship changing its inertial reference frame. That is an absolute thing.

Also, if the spacehip returns to Earth and its crew are younger than their Earthbound contemporaries, then that is called differential ageing. That's not, strictly speaking, time dilation.

 

[FactChecker]

You are not aware or affected by your own inertial motion. Your reference frame can be considered stationary, so your water will last as long as you ignore external measurements of time and use your own clocks to determine when to drink.
Any relativity effects are only apparent to those in other inertial reference frames. They would say that you have not synchronized time correctly in different positions along your direction of motion. In their time, you are drinking water slower than 1/their_month. By their time measurements, you also take longer to get to your destination than you think. So it all balances out.

[Edit] I overlooked that the original distance measurement was in the Earth reference frame. I will have to rethink this.