Tag Info

New answers tagged

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 ...


0

If it is admissible the question and answer to 'How old is the universe ?' then we can not drop the absolute time notion. I can elaborate on other ways but one reason is enough to justify my answer.


0

How can we justify dropping the absolute time hypothesis? By simply looking at what clocks do. A clock doesn't actually "measure the flow of time". It isn't some cosmic gas meter. The passage of time is just a figure of speech. A clock clocks up some kind of regular cyclical local motion and displays a cumulative result that we call the time. Time is a ...


1

"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 ...


-1

I can only offer an opinion rather than a peer-reviewed authoritative response. But I hope it's of some use. We can read various descriptions about falling into a black hole, such as this on Baez. There's also Andrew Hamilton's website. I'm afraid to say I think they're wrong. Take a look at The Formation and Growth of Black Holes on mathspages, and you can ...


0

No, relativity is about reference frames. The person falling into a black hole will pass through the event horizon, but due to time dilation, no one else can observe it.


0

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 ...


0

It is not just absolute time that is being thrown out the window, it is also absolute rest and absolute motion being tossed as well. But to start, it must be understood that Time is a dimension. It is 1 dimension of the 4 dimensional structure known as Space-Time. If you are moving across the dimension of time, then time passes by. If however, you were able ...


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 ...


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

if A and C are moving at equal velocities 5c then they should meet B at the same time ,If the stationary object B stands at the mid point of the motion path then A will cut the track to B at 5c and C will do the same so suppose that half the distance is 5 kilos then Then both A will meet B and C after 1/c time ..so the velocity each one will see the other ...


0

We know particles that exists outside of time: Photons, travelling at the speed of light, see their path (and their lifetime) relativistically contracted to a point (and an instant of no duration). It must obviously be mathematically possible to describe what happens to a photon in its own rest frame. We just do not know how: Just changing our frame of ...


0

No complete formulation of physics without time is possible. To be physical, a formulation must explain and predict the observable universe, of which time is a fundamental feature. In a timeless formulation, no quantities can change and no events can cause or be caused. Since we overwhelmingly find that quantities do change and events have causal relations ...


0

I suppose the only way you could "sync" a particle with a clock is to measure a phase (for example a time-dependent one accumulated by an upper state with regard to a lower state for virtue of having a difference frequency $\Delta \nu = h \Delta E$). Then this phase might tell you (a bit) about the time offset that you would have had to apply to use this ...


1

suppose it is possible to accelerate matter at speed of light By this you must mean suppose that relativistic mechanics is, at its root, wrong. What will the time reflects on these two clocks? Since you've stipulated that relativistic mechanics is wrong, which incorrect, non-relativistic mechanics would you like to apply to this problem?


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


1

As @Hypnosifl points out, a single event cannot have $\Delta t$. You must define two events such as a light flashing or the beginning and end of a process or a particle moving from point A to point B. You must the define the pair of events (call them $A$ and $B$ with both a time coordinate and a spacial coordinate, e.g. $$ \pmatrix{ct_A \\ x_A} \text{ and } ...


2

The basic confusion is in your comment that "During $\Delta t_3$ an event occurs in $O_3$'s frame that is measured as $\Delta t_2 = \gamma^\prime \Delta t_3$". In SR a single "event" occurs at a single point in spacetime--an interval like $\Delta t$ can only describe the time between a pair of events. What's more, the time dilation formula $\Delta t_B = ...


0

I personally like the view pesented in this paper. So, different snapshots of the universe at dfferent times, should actually be considered to be different universes which are related to each other by being correlated. While awkward from an intuitive point of view, it is a far more natural from the point fo view of quantum mechanics.


1

In classical mechanics, time is the unique parametrisation of dynamical systems. In relativity theory, one then sees that time is somewhat more than this, because there exists a global symmetry (the Poincaré-group) that involes time and space on an equal basis (called spacetime). Also, one can show that parametrisation by time is not the only way to do ...


0

"Time" is very difficult to define properly, in General Relativity time is the 4th dimension of what is known as "spacetime" and this dimension is one which you may only move "forward" and you must move through spacetime at the speed of light, which is why time slows down as you move near the speed of light. Other than this, time is not well defined; you ...


-2

The idea that space is expanding is a relation between it's size and time. Time expanding would be a relation between time and time, so it can't???


4

It's really an either/or proposition, i.e. either space is expanding or the time experienced by distant objects is dilated, depending on how you view the situation. We choose the former description because it is better. To expand (excuse the pun!) on what I mean, the measurable result of time dilation is red-shift and indeed distant cosmological objects ...


0

You ask Is there more time, longer time or is the time part not affected at all by expansion? First off, Is there more time? I don't know because I dont know exactly what time is? Do you? Did Einstein? No, I think he said he didn't in one of his books? Does anybody? Probably not. Is there longer time is an easier question because I don't think that ...


1

You are entirely correct: when assigning JD real numbers to UTC calendar dates, it is simply impossible to name any moment during the leap second — while an analog rendering of a UTC time can say “23:59:60.25”, the JD will provide no name for any moment of that entire second. This can be seen if you visit the standard JPL HORIZONS system: ...


0

Let me take my idea of what i think are your assumptions as far as I can. From your question "The way I understand it, I'll illustrate with a simplified example. Say I am a point particle. At any one moment in time, I can take 2 states. Then time progression would be a binary tree, where any "descendant" of me in the branches would be different from the ...


2

You raise two issues: ΔT, and the HORIZONS timescales. Let us tackle each in turn. 1. What is Delta-T? You are correct that HORIZONS is using a confusing term here. What the HORIZONS menu calls Delta-T is an entirely different quantity than the ΔT you will see defined and used in many other references on astronomy. Briefly: What HORIZONS calls Delta-T ...


2

The uncertainty principle is still true in its usual form, but it refers to your knowledge of the state. Suppose your state is just one electron, you can confirm this if you observe the system for a time $\Delta t$ and you don't see additional particles. However, due to the uncertainty principle you can only measure particles that increase the energy of the ...


9

There is a 1961 paper by Aharonov and Bohm on this subject, in which there is defined, among other things, a characteristic time for an operator's expectation value to deviate significantly, measured by the initial dispersion in that operator. This result is essentially a theorem we will prove here (Theorem 2). Let $\mathcal{S}$ be a Hilbert space, $A$ a ...


0

Time is not an operator, s.t. this type of uncertainty relation differs from the usual form, in which participate operators. (There are though attempts to define time as an operator in time-arrival problems). And though, in nuclear physics we are well acquainted with unstable (radioactive) nuclei. The unstable nuclei are so-called resonant states, and the ...


3

Ok, so the Energy-Time "Uncertainty Principle" is often way misrepresented, but it does mean something. In $\Delta t \Delta E \geq \frac{\hbar}{2}$ the $\Delta t$ represents the amount of time is takes for the energy expectation value to change by one standard deviation. It does not represent a measurement. Note: This is explained in Griffith's "Quantum ...


0

Check Shape Dynamics. In some sense, time doesn't exist in this formalism.


0

The proof is very simple. But for the answer you must ask first: what is time? And that is a bit more difficult. In special relativity (Minkowski diagrams) we currently distinguish between the observed time and the proper time. Observed time is only relative to each observer, but it has the advantage that we can build up a time axis, permitting to say that ...


0

The relativity of simultaneity is not an axiom, the axiom is that the light velocity is the same in every frame of coordinates. A spot of light travels at the same velocity, c with respect to you, and at the same velocity $c$ with respect to a traveler traveling with respect to you at an arbitrary velocity. So, assume that you send two spots of light to ...



Top 50 recent answers are included