# Tag Info

2

Usually, when you want to probe the lifetime $\tau$ of a particle (or a quasi-particle), what you basically do is looking for the way the associated wave-function $\psi$ is significantly decreasing : $$\psi\sim\psi_0\,e^{-\left(\frac{1}{\tau}+\,i\frac{E}{\hbar}\right)t}$$ Let us consider a free particle with a given energy $E$. As $\langle E\rangle=E$ is ...

0

Let's say you're the one accelerating towards the other person who is at rest, so after meeting him you're clocks wouldn't agree because of time dilation, right? Let's make the thought experiment more precise. In some inertial frame of reference, a moving clock is located at $x = 0$ when both the coordinate time $t$ and the moving clock time $\tau$ ...

0

All inertial reference frames are equivalent. This is the most basic assumption of Special Relativity as well as Newtonian Mechanics. This means that if you are in an inertial reference frame, say, a car moving with constant velocity, you can never tell if the car is moving or not (unless you look out of the window of course). This is not true for a ...

0

Time dilation is linked to motion. Be it from acceleration, or velocity, or both. It is because the speed of light is invariant for all observers. If this speed is the same, then what changes is 'time.' As for the who experiences time dilation, the answer is both of you. You both feel time dilation with respect to each other. Time dilation is not 'whoah ...

0

The difference between unaccelerated (which includes stationary) and accelerated state is that in case of the latter you can actually feel (and measure) the force causing acceleration. Example: Without looking out the window, you cannot tell whether the train you are in is currently moving or not (relative to Earth) unless there is some acceleration ...

1

Extensive googling hasn't helped me to understand how this observed earth rotation angle is used to compute UT1 As explained in: this lecture Earth's angle of rotation = 2π(0.7790572732640 + 1.00273781191135448(Julian UT1date - 2451545.0)) radians. So one observes Earth's angle of rotation and calculates the Julian UT1 date as a decimal date from that ...

0

Anywhere there is energy there is time dilation. But you have used a linear approximation - which may hide the super - tiny effect of time change as a wave runs though a region of space. In other words, if there was a beam of gravity waves, and one person was in the waves, the other not, the person who experienced the waves would have a small difference ...

0

First, to clear something up, the amount of work done does not depend on the amount of time a force is applied, but on the distance over which the force acts. If you and your friend, Alfred, use the same force to push a block from point A to point B, but it takes you ten years and Alfred ten seconds, you both end up doing the same amount of work, and hence ...

0

Exerting a force over a time interval is not always related to energy being put into the system. The amount of energy given to a system by a force is called the work. This is computed by calculating the projection of the force onto the displacement made by the object. $$\text{(Change in Energy)} = W = \vec{F}\cdot d\vec{l} = F dl \cos(\theta)$$ This ...

0

In general, it takes no energy to apply a force. Energy is described as the potential to do work, which has the same units as energy. Work is defined as a force applied during some distance. From these definitions, it is clear that the duration of the force does not directly impact how much energy is required. For instance, Earth exerts a force of gravity ...

0

The energy you input is equal to the work you perform, that is force times distance. Thus the energy will grow if you continue to apply force and the system on which you apply force continues to move. The rate at which you bring this energy to the system per unit of time is the power, if it is constant through time, then energy equals power times duration. ...

-3

Energy equals mass multiplied by the speed of light squared, and mass equals energy divided by the speed of light squared. What goes up, must come down. Nothing can escape a black hole. Every action has an equal and opposite reaction. Energy cannot be created or destroyed, it only changes form. All things in an enclosed system gain entropy, slow down, ...

-1

The simplest idea is that the collapse of the previous universe caused the big bang. I imagine it as black holes smashing into each other at great speed, immediately causing a nuclear reaction. There are some unproven theories that need to be adjusted, such as the idea that dark energy density remains constant as space expands. Black hole radiation has ...

0

Think of it as a resistors in parallel problem. You have a heat source inside the room and a constant temperature outside (if you assume that the outdoors is infinite and well connected to the walls. Then you have a thermal resistance/area for the wall, ceiling and floor material. Using the total area you have an overall thermal resistance and a ...

0

You are confused about what is called the Observer Effect. Read about it from here Observer Effect. Also, read some parts of this. The Uncertainty Principle just says that there is a fundamental limit to which the position and momentum of an object can be measured. Also, as PhotonicBoom said, the Observer Effect for Quantum Mechanics is not experienced at a ...

0

A clock is a collection of particles that behaves classically, i.e its a combination of all the wavefunctions of its particles, and due to that "coupling" it does not behave probabilistically anymore. You are refering to the phenomenon of wavefunction collapse due to a conscious observer, but in reality decoherence occurs. Wavefunction collapse happens in ...

0

What muddies the waters a bit are that when I tried to search for the borde-guth thing, the first result was a Christian site, and of course when it was discovered that the universe was expanding, the big bang was taken by many Christian scientists as the creation of the universe by God, and that is still the most likely explanation for why the universe ...

0

In an inertial frame , the clocks at different points of space are synchronized. This synchronization issue is important. Once you synchronize Indian time with the American one, there is no paradox. So it is not a time travel. Anyways , the question was interesting.

0

No, this is not time travel. Imagine you start in India and adjust your watch to US time before you leave. Nothing has changed. You have neither gained nor lost time, but when you get to the US your watch shows the correct local time.

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Time Travel does not mean going from one time zone to another. You did not get those 6.5 hours back again, they just appear to be back to you because you entered a different time zone. I think this definition of Time Travel by David Lewis’ is perfect and will explain why you are wrong: An object time travels if and only if the difference between its ...

0

If you leave earth at age 30 and live for 30 years near a black hole, time will pass more slowly for you and normal for the people on the earth. I don't know the exact age you will be when you spend 30 years near a black hole, but when you return to earth you will be younger than others who had the same age as yours when you left. In other words, others at ...

6

The time used in describing the evolution of the universe is comoving time. This is the time that would be measured by a freely moving observer on their wristwatch (assuming the high temperatures didn't melt both the observer and the wristwatch :-). Time is not a simple thing to define in general relativity, however we can always unambiguously define proper ...

19

This is a common point of confusion, not only with regards to inflation, but any time an expanding universe comes up... The "cosmic speed limit" as you call it says that no particle or signal can move through spacetime faster than the speed of light. Spacetime is a very specifically defined thing, described with a coordinate system. There is no restriction, ...

2

Here is a diagram that describes what happens when a photon hits your eye. It is in two dimensions, one is time the other is space. The photon interacts with the electromagnetic interaction with an atom in the retina of the eye, where the electron which is bound in the atom goes to a higher energy level and the photon is absorbed giving its energy to ...

5

There is some discussion about this in the question How does a photon experience space and time?. You'll commonly hear it said that photons don't experience time, but this is somewhat misleading. Observers moving at different velocities have different coordinate systems, and these systems are related by the Lorentz transformation. If you apply the ...

0

The subsolar point is the point on the earth's surface where the sun is directly overhead. The formula you give uses the longitude of this. Take the difference of this from the longitude for the poles of whichever geomagnetic reference model you are using.

-1

Oliver Heaviside showed in the end of the 19th century, that if the gravity field travels at a speed, then it behaves much the same way as the electric field: that is, magnetism is a consequence of the electric field travelling at a fixed speed, and likewise, co-gravitation or gravitomagnetism is a consequence of gravity of gravity travelling at a speed. So ...

1

No. The standard metric for cosmology is given by: $$ds^{2} = - dt^{2} + a(t)^{2}\left(d^{3}{\vec x}^{2}\right)$$ where the term inside the parenthees represents the 3-metric of a homogenous three space. As you can see, there is no difficulty with evaluating the age of the universe: $$T = \int\sqrt{-g}\,\,x^{a}y^{a}z^{a}\epsilon_{abcd} = \int dt$$ ...

0

Can I suggest a different way of doing this? The first thing you should always do with experimental data is graph it to get an idea what it looks like. The graph of your data looks like: The blue dots show the data points, and they obviously lie on a straight line (give or take experimental error). So I used linear regression to fit a straight line to ...

0

Our perception of time is irregular. "A watched pot never boils" and the effect of being able to perceive minute details when in a crisis - pebbles shot from a wheel and the colour of a band around the tyre as you are about to be run over for example.

0

Is the flow of time regular? Picture a leaf floating downstream on a river in the pitch dark. As the river gets narrow it speeds up, and as it gets wider it slows down. The leaf has no light to see the shoreline so from it's perspective there is no change in the flow of the river. Now what if the light turned on? The leaf could now see the shoreline, ...

0

The event horizon of a black hole is a very weird and complicated place. According to my undergrad GR course, at the event horizon of a black hole, time becomes a space-like coordinates, and space becomes a time-like coordinate. From what I remember, a time-like coordinate is one in which you absolutely have to move forward. Therefore, beyond the black hole ...

5

You can define the age of the universe roughly as the proper time for a hypothetical observer who is comoving with the galaxies and not too near a strongly gravitating object. This is imprecise because the galaxies are themselves moving around and the age would depend on exactly the worldline of the observer and how it moved to avoid heavy objects that ...

1

My favorite POV on this I derived from reading Hawking's bestseller. Consider yourself in two possible states $A$ and $B$ of the universe. The more information about state $A$ does your mind(brain, ...) in state $B$ possess(have records of, ...) the more you feel in state $B$ that state $A$ is past(remembered, ...) Thus time is about having information. ...

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An observer with zero comoving velocity (i.e. zero peculiar velocity). Such an observer can be defined at every point in space. They will all see the same Universe, and the Universe will look the same in all directions ("isotropic"). Note that here I'm talking about an "idealized" Universe described by the FLRW metric: \mathrm{d}s^2 = ...

0

As BICEP2 has shown, spacetime has been significantly irregular, enough to change how electromagnetism propagates. Especially considering relativity, time is not regular. Deviations from a "uniform rate of time" are not easily observed, but different rates are now measured daily worldwide: GPS must account for a small (per second) rate difference between ...

0

Under Special Relativity the flow of time should be inferred to be regular for a single observer because the speed of light is invariant with regards to the single observer. Observers in the same reference frame will measure the same value for the speed of light, and as a consequence experience the same flow of time. Your perception of time may vary as ...

2

Absolutely no. The best known counter-examples are the clocks on board the GPS satellites. If the flow of time was "regular" , they'd run just as fast as any other clock. In reality, they run slower - precisely as predicted by relativity theory. So there's a clear discrepancy between us down here and a satellite that's just a few hundred kilometers up.

-1

Energy, Space and Time all are granular. The difference betwenn them are the unbelievably small dimensions of the smallest space and time steps, as opposed to the rather largish smallest energy quantum h. Which is large enough to have been proven experimentally 100 years ago. (Which is what earned Einstein his Nobel prize.) The granularity of time and ...

0

Some Richard Feynman quotes which I think clarify the scientific view on this sort of question: "Religion is a culture of faith; science is a culture of doubt." "I can live with doubt and uncertainty and not knowing. I think it is much more interesting to live not knowing than to have answers that might be wrong." Physicists have learned a lot about the ...

1

The "scientific view of creation" is the Big Bang. It's as widely accepted as gravity. Nobody doubts it exists, we're mostly discussing how it works. As for the conservation of energy, that basically states that at two points in time the total amount of energy is equal. You need those two points, though. And there is no proof that there is a point in time ...

35

Note: This answer addresses the question in its original form: Is the flow of time regular? How would we come to know if the whole universe along with everything in it stops for a while(may be a century). Is there a way to know if flow of time is smooth,or irregular? Flow with respect to what? Regular with respect to what? How would we ...

0

Since practical science creates mathematical models to describe the observable reality as good as possible, the question of creation is quite irrelevant here. Nonetheless it might be interesting philosophical question how a "physical creationism" might look like while acknowledging what we know scientifically in physics. The physics department of the ...

21

Have a look at my answer to Is there a proof of existence of time?. The problem with your question is that the concept of the flow of time is an elusive one. We measure flows with respect to time, for example velocity is $dx/dt$. So how can we measure the flow of time? If we simply say it's $dt/dt$ then obviously that is always one. The only possible ...

3

The simple answer is that in our everyday world where velocities are much smaller than the velocity of light, yes time is as regular as space. If you rule a football field as 100meters by 100 it will stay that way whenever you measure it ( unless there is an earthquake of some such disruption). We have rulers defined in France for the meter, and we have ...

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