Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in the conscious experience. Time is often referred to as a fourth dimension, along with three spatial dimensions.Time has long been an important subject of study in religion, philosophy, and science, but defining it in a manner applicable to all fields without circularity has consistently eluded scholars.
Nevertheless, diverse fields such as business, industry, sports, the sciences, and the performing arts all incorporate some notion of time into their respective measuring systems.Time in physics is operationally defined as "what a clock reads".The physical nature of time is addressed by general relativity with respect to events in space-time. Examples of events are the collision of two particles, the explosion of a supernova, or the arrival of a rocket ship. Every event can be assigned four numbers representing its time and position (the event's coordinates). However, the numerical values are different for different observers. In general relativity, the question of what time it is now only has meaning relative to a particular observer. Distance and time are intimately related and the time required for light to travel a specific distance is the same for all observers, as first publicly demonstrated by Michelson and Morley. General relativity does not address the nature of time for extremely small intervals where quantum mechanics holds. At this time, there is no generally accepted theory of quantum general relativity. Time is one of the seven fundamental physical quantities in both the International System of Units (SI) and International System of Quantities. The SI base unit of time is the second. Time is used to define other quantities – such as velocity – so defining time in terms of such quantities would result in circularity of definition. An operational definition of time, wherein one says that observing a certain number of repetitions of one or another standard cyclical event (such as the passage of a free-swinging pendulum) constitutes one standard unit such as the second, is highly useful in the conduct of both advanced experiments and everyday affairs of life. To describe observations of an event, a location (position in space) and time are typically noted.
The operational definition of time does not address what the fundamental nature of it is. It does not address why events can happen forward and backward in space, whereas events only happen in the forward progress of time. Investigations into the relationship between space and time led physicists to define the spacetime continuum. General relativity is the primary framework for understanding how spacetime works. Through advances in both theoretical and experimental investigations of space-time, it has been shown that time can be distorted and dilated, particularly at the edges of black holes.
Temporal measurement has occupied scientists and technologists, and was a prime motivation in navigation and astronomy. Periodic events and periodic motion have long served as standards for units of time. Examples include the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum, and the beat of a heart. Currently, the international unit of time, the second, is defined by measuring the electronic transition frequency of caesium atoms (see below). Time is also of significant social importance, having economic value ("time is money") as well as personal value, due to an awareness of the limited time in each day and in human life spans.
There are many systems for determining what time it is, including the Global Positioning System, other satellite systems, Coordinated Universal Time and mean solar time. In general, the numbers obtained from different time systems differ from one another.
Hi All,
I am doing a linear regression in Excel 2007. It is not available within the usual settings so I must. Edit: activate , an add-in called (Duh) Edit' Analysis Toolpak'
What seems strange is that I have to install it each time I use it so that it seems to be installed only when the...
I have a speed estimator that calculates a cyclist's Steady State Velocity v given the rider's power output p (watts), rider mass m (kg) and hill gradient g. For this particular model, headwind and tailwind beyond the drag force conditions are not relevant.
In the model I use, there are three...
Hi all.I would like to know about "binning window".
This paper I'm reading says like this.
Why do "convolving the data with the ##b(t)## before the sampling" and "binning into time bins with a width ##δt##" have the same meaning?
I know I'm addicted to post to PF 😅
But this forum is so...
I tried to calculate the time the charged particle will take to reach the plane using the a and using d=1/2at² and found the t to be equal to root(4εmd/σq).
I guess the time period of oscillation will be double of t (by symmetry), i.e. 2root(4εmd/σq). I don't know if this is correct.
A and B leave their places and start moving towards each other. If they are 50m apart after both 2 min and 3 mins, how far are their places?
I can able to draw a diagram for this problem:
Take distance between their places as D
Speed of A = x meter /minutes
Speed of B = y meter/minutes
So...
Problem: You are playing soccer with some friends while some people nearby are playing hide and seek. When the seeker gets to '4', you kick the soccer ball high in the air. WHen the seeker says '5', the ball is 10 ft in the air. When the seeker gets to '7', the ball is 20 feet in the air. How...
What feature of the equations of classical physics show that space and time are fundamental and how would the equations differ if space and time were not fundamental but emergent? I heard all of this from a previous talk and I would appreciate any help and any further reading recommendations.
Good morning,
I'm trying to workout the time for an element to diffuse at set distance in microns.
I have the distance, the diffusion coefficient, just unsure which equation I actually use.
X= sqrt DT or the other one x= sqrt 2DT.
I can't seem to figure out when you use one and not the...
1. So for an asymptotically far-away observer, something falling towards a black hole will never reach it
2. However, the thing falling in will reach the event horizon is finite affine parameter
3. The Universe has a finite age for an asymptotically far away observer
a) Does this mean that one...
The is a question about gravitational time dilation and escape velocity. As others have pointed out, you may use escape velocity to calculate gravitational time dilation in a gravitational field. (Interestingly, you can't use gravity to calculate gravitational time dilation, which makes...
I already found ##I(t)## using Kirchhoff's laws, I got the equation ##V-RI-L\frac{dI}{dt}=0\Rightarrow L\frac{dI}{dt}=V-RI## then I solved the differential equation getting ##I(t)=\frac{V}{R}\left[1-e^{-\frac{R}{L}t}\right]##. My problem is founding the voltage as a function of time ##V(t)##, I...
I am performing some calculations but struck with confusion whether I am doing it correct or wrong due to contradictions of these calculations on different calculators websites. I hope here someone will help me with the validation of my calculations.
Battery Capacity = 150 Ah
Battery...
I have a copper cylinder that is at 0C, how much time will be needed for it to equilibrate with 10kg of water at 75C?
Copper cylinder:
Mass: 105.7 g
Specific heat: 0.385 J/gC
Initial Temp: 0C
Final Temp: 75C ish
SA: 25 cm^2
Water:
Mass: 10000g
Specific heat: 4.184 J/gC
Initial Temp: 75C...
My problem started when I took my alternator apart to grease bearings when I put it back to together dash light came on so took it apart seen wire to one of the brushes was broken soldier back together
it work for a short while the light was back on seen soldier had broke again so I changed...
Summary: S5-HVS1 travel time
If S5-HVS1 is going 10 times faster than the rest of the stars of the milky way, does that mean that time is going slower than us?
How much slower is time going, 10 times?
Scenario: Three types of scifi hyperdrives are available to you.
Class I: A small drive that can be fitted on small vessels. Hyperspace travel time is a lightyear covered per 30 minutes. Yet in reality, outside 30 days passes for every 30 min of hyperspace travel. So about 2 hours would get you...
with distance between planets as 4x10^8m measured by you on the ship
My attempt:
t' = γ(t - ux/c^2)
γ = 5/3
u = 0.8c
t = 0.9s
x = 4x10^8m
answer is: -0.278
Therefore not possible
My question is what if we traveled rightwards, from p2 to p1, would the answer change?
Should my above information...
I'm having a hard time understanding how exactly to evaluate the expression}
$$\partial_t \mathcal{T}\exp\left(-i S(t)\right)\quad \text{where}\quad S(t)\equiv\int_{t_0}^tdu \,H(u) .$$
The confusing part for me is that if we can consider the following:
$$\partial_t \mathcal{T}\exp\left(-i...
Given the example g = \frac{GM}{R^{2}}, we may compute the change in field strength if the mass is changed by a small amount dM to be$$dg = \frac{G dM}{R^{2}}$$and also if R is changed by dR,$$dg = \frac{-2 GM dR}{R^{3}}$$If, however, both the mass and radius are changed by a small amount at the...
Hi,
Can anyone please help me with the following:
I have found the velocity of projection, no problem, it is v = 2*sqrt(10)
Also, in obtaining this value, I have also found the extension in the string when in equilibrium, it is x = 2
Now on to the time of flight.
The given answer is: t =...
I able to calculate this 2 things:
relative speed of A and B = 3 + 1; 4m/sec
Time for meeting for first time in opposite direction = 100/(3+1); 25 sec
I can't able to find distance in Meeting for first time for opposite direction.
I have a question relates to a 3 levels system. I have the Hamiltonian given by:
H= Acos^2 bt(|1><2|+|2><1|)+Asin^2 bt(|2><3|+|3><2|)
I have been asked to find that H has an eigenvector with zero eigenvalues at any time t
First, create a rocket ship with:
* a clock
* a 3-axis accelerometer
* a computer
* a 3-axis external thruster
The rocketeer begins in Earth orbit and sets the clock to Earth time. Then the ship takes off on a random trip through our universe. The pilot will arbitrarily point and apply the...
Hi everyone,
I’m a student in Ireland and I’m still in high school and the teachers were saying that its finally time for us to choose what paths we should take in terms of choosing subjects for our final high school years. Now my main question is that should I become an astrophysicist...
I can show that ##\frac{d}{dt} \langle \psi (t) \vert X^2 \vert \psi (t) \rangle = \frac{1}{m} \langle \psi (t) \vert PX+XP \vert \psi (t) \rangle##.
Taking another derivative with respect to time of this, I get ##\frac{d^2}{dt^2} \langle \psi (t) \vert X^2 \vert \psi (t) \rangle = \frac{i}{m...
For instance, if a stream of muons were released from a box near a massive object and traveled on a straight path slowly (at a non-relativistic velocity) away from that object, a faraway observer would notice that the particles would take longer to decay than a muon typically would in empty...
I couldn't match this question with another topic, so I made a new topic.
Suppose we have past H and present P at a certain moment. In present P a measurement is made. For matter of speaking we adopt MWI, so we have the two measurement outcomes A and B diverging in two realities A and B in...
do parralel timelines have to run concurrently to our time? what I mean by this is basically if there is a version of me or you out there in a parralel universe right now in 1963 for example just living like normal or do all parralel timelines have to be in the same timeframe as us?
I am assuming this is the interaction picture, so I start with $$|\psi>=c_1(t)|1>+c_2(t)|2>$$. Plugging this into the Schrodinger equation,
I get the equations $$i\hbar c_1(t)=<1|H'|2>c_2(t)$$ and $$i\hbar c_2(t)=<1|H'|2>c_1(t)$$. I am assuming H' (the perturbation) is $$H'= − f(t)[...
How did you find PF?: youtube
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i need a falling mass over time /joules per kilo over 1hr time
also need to know how to figure gearing to maintain fall over time in regards to a set resistance such as a 5 kw alternator
Firstly, I calculated the relative speed between the two rockets, finding v=1.6c/1.64. Then, I applied the length contraction: the length of the moving rocket will be 0.6L due to this phenomena, so the total distance traveled by one rocket, with respect to the the other, will be 1.6L. Therefore...
I got acceleration by dividing force by m then replaced a by dv/dt and then integrated it to get velocity as a fxn of time and hence got kinetic energy but problem is my ans does not match with any option can someone please compare their ans
vy=vter + (vy0 -vter) e-th/τ where tau=m/b EQ 1
Okay, for part a, I used Eq 1
I let vy=vy(th)=0 --->The reasoning is that the projectile would stop moving for a short time when it hits the incline, but I have a feeling that reasoning is faulty
I let vy0=v0sinθ
Then the equation became...
Hi, I am struggling with a calculation.
A boat costs x to maintain and I and a friend decide to split the costs 60/40, where I put in 60% of the cost.
However, I will have the boat less than my friend, he will have it 3/8 of the time and I will have it 5/8 of the time.
So what is my actual...
Hi,
I'm a 3rd year (Scottish so a 4 year undergrad degree) student doing Physics. Obviously many of you will have been through a Physics/Maths degree and this question is for you.
I'm finding that the volume of content this year is so much that I spend all my time keeping up on course notes...
An electric field E(t) (such that E(t) → 0 fast enough as t → −∞)
is incident on a charged (q) harmonic oscillator (ω) in the x direction,
which gives rise to an added ”potential energy” V (x, t) = −qxE(t).
This whole problem is one-dimensional.
(a) Using first-order time dependent perturbation...
I actually have a solution available to me, but I don't understand what it's doing so I'll include my attempt at a solution and briefly describe the correct solution that I don't understand.
ΔE Δt ≥ ħ/2 (Uncertainty)
ΔE = hΔf (De Broglie)
ΔE = hc/Δλ
Substituting,
(hc/Δλ)Δt ≥ ħ/2
Rearranging...
I was not able to derive the charge on the capacitor. But then, I arbitrarily assumed ##\phi=B.A## (Dot product of Magnetic field and Area)
Then, proceeding as follows,
##\phi=BA\cos(\omega_0 t)##
##\frac{d\phi}{dt}=−BA\omega_0\sin(\omega_0 t)##
Now at ##t=0, \phi=BA\cos(0)=BA##
Therefore...
Comparing high precision atomic clocks, one flying in a airplane and one on the ground had demonstrated permanent time dilation presumably due to special relativity (speed) and/or general relativity (gravity) .
While similar experiment with a ruler would demonstrate length contraction only...
Hi,
I recently learned that if you can travel at the speed of light, or nearly, you can reach the Andromeda Galaxy within 30 years, due to time dilation and bypassing 2.5 million years on Earth. Is this true?
I've already posted this question on the mathematics website of stack exchange, but I've received more help here in the past so will share it here as well.
I am developing a tool for missile trajectory (currently without guidance). One issue is that the aerodynamic equations on the missile are...
Recently I've started reading Weinberg QFT, Vol 1, to introduce myself better to quantum field theory, after finishing courses in qft at the university. Reading through the second chapter, I've found myself confused by his treatment of degenerate multiplets in Appendix C. Here is the equations...
If a medium with speed of light ##c_1## is considered, shall the Lorentz transformation be considered relative to it or to speed of light in the vacuum ?
I don't know if we could send particles like muons through water for example, to check this with their life time.
Summary: Olympic problem from kinematics
Hello,
could anyone help me with the following problem? I don't quite get how exactly does it work.
After being kicked by a footballer, a ball started to fly straight towards the goal at velocity v = 25m/s making an angle α = arccos 0.8 with the...
Hello, my name is Jack and I'm a year 11 student in Australia. After listening to, and reading some information regarding quantum entanglement, I'm still a little unsure about the solution to a thought experiment:
Let's say that I create a situation in which multiple pairs of particles are...