# Tag Info

5

One piece of physics that you've missed is the most pulsars spin down due to the emission of magnetic dipole radiation. For instance, the crab pulsar has a period of 33.5028 (plus a few more sig figs) milliseconds, but slows down by 38 nanoseconds per day. Furthermore, the size of several more increasing order derivatives is known accurately. So in ...

3

The link Qmechanic has suggested is a duplicate and does discuss the question you ask. However there is another point that is worth making here. In general relativity we describe the universe as a manifold equipped with a metric, and the metric is the FLRW metric that desciribes expanding spacetime. However the FLRW metric does not include the point(s) at ...

3

The experiment is real. If you take an atomic clock that is accurate and stable enough and you fly it around the world, it will disagree with an identical clock that has remained on the ground. This is because of the combination of two effects: relativistic time dilation, which means that any clock that moves will run more slowly compared to one that's ...

3

Yes, in a sense, clocks are always wrong, namely in the sense that finding two that "agree" by continuously always showing the exact same time would require a very peculiar arrangement, crucially involving the observer's speed and position relative to the clocks! However, physicists have adopted another sense of what being simultaneous (or clocks agreeing) ...

3

To measure time, a duration, you need two moments – when you press "start" and "stop" button on the stopwatch, respectively. But because the two objects are moving relatively to each other, it isn't possible for them to "meet" at both moments. If their locations coincide at the "start" moment, for example, so that their clocks may be compared at this "start" ...

2

"Unfortunately, due to time dilation the time for mass to fall into the event horizon becomes infinite, so that nothing can cross the horizon within in the life time of the universe." This can not be understood as any objective statement about coordinate-independent physical realities, since it's only true in certain coordinates like Schwarzschild ...

2

Is time an illusion? No. I think it's best to think of it as something like heat. You know what heat is, especially if you put your hand on a stove: szzz aaargh! Heat is definitely not some illusion. However it is an "emergent property". Think about the kinetic theory of gases. The temperature of a hot gas is something like a measure of the average kinetic ...

1

Hard to know why you got a different answer in your calculation, but here are some general considerations. Assume you have a circuit like this: You would think that you can easily compute the time constant $\tau = R_1 C_1 = 10^{-4}s$. However, it is most likely that your real circuit isn't actually like this. First - capacitors are notoriously ...

1

Yes, both special relativity and general relativity have to be taken into account. The total time dilation is given by $$\frac{\text{d}\tau}{\text{d}t} = \sqrt{ \left(1 - \frac{2GM}{rc^2}\right) - \left(1 - \frac{2GM}{rc^2}\right)^{-1}\frac{v^2}{c^2}},$$ where $\text{d}\tau$ is the time measured by a moving clock at radius $r$, and $\text{d}t$ is the ...

1

Where is the flaw in my thinking? In your concept of time. It's little more than a cumulative measure of local motion, see A World without Time: The Forgotten Legacy of Godel and Einstein]. Your macroscopic motion relative to some other guy results in you measuring his local motion to be slow, whilst he measures your local motion to be slow. This sounds ...

1

Identical frames? Yes! So, let's disregard technical feasibility, and assume we have something similar to a CCD camera sensor, but made of unobtanium, and just "fast enough", always. I will call it uCCD. It has no thermal noise, of course. Now, we take a normal picture, with shutter set to 1/60 of a second. What did the uCCD sensor do? Each pixel collected ...

1

force = acceleration * mass, hence acceleration will be $a=50N/22kg \approx 2.27m/s^2$ Distance it moves might be found by integration: $\int_0^{1.2}v(t)dt=\int_0^{1.2}atdt$, since speed $v(t)=at$ Answer to (B) then is 1/2*1.2*(2.27*1.2)=1.63, which seems pretty close to what you have got

Only top voted, non community-wiki answers of a minimum length are eligible