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Questions tagged [order-of-magnitude]

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Order of magnitude of time derivatives of gravitational potential and gravitational vector potential on Earth

[This question is connected with this one. Since the estimation and measurement of spatial gradients and time derivatives have very different levels of difficulties, I thought it best to ask two ...
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Order of magnitude of gravitational vector potential & its gradient on Earth

In post-Newtonian approximation of gravitation, the metric on and around the Earth is taken to have the expression $$ \begin{bmatrix} -1+\frac{2}{c^2}U+ \frac{2}{c^4}(\psi-U^2) + \mathrm{O}(c^{-5}) &...
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-6 votes
2 answers
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Do people have an attractive force?

The definition of gravity is this from google: "the force that attracts a body toward the center of the earth, or toward any other physical body having mass." Ok what about the actual ...
user55665484375's user avatar
1 vote
1 answer
69 views

Order of magnitude of $v=\sqrt{q^2/Mr}$

I'm developing a problem and already found the solution, I know is correct to assume in my problem that the velocity of an electron is: $$v=\sqrt{\frac{q^2}{Mr}},$$ where $q$ is the charge of the ...
Mango Mugger's user avatar
1 vote
2 answers
94 views

Is overusing gravitational slingshots a real concern?

I was thinking of the trading of kinetic energy during a gravitational slingshot maneuver and wondered if the kinetic energy lost during that process makes any noticeable impact on the orbit of the ...
AeroMain27's user avatar
10 votes
5 answers
4k views

Why has it been so hard to come up with testable predictions for string theory? [closed]

String theory has yet to come up with any easily testable predictions despite decades of work. Why is this? Why is it so difficult to come up with testable predictions for string theory? Why is it ...
blademan9999's user avatar
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14 votes
2 answers
2k views

What are the experimental difficulties in measuring the Unruh effect?

The Unruh effect was predicted in 1976. As someone with no background in experimental physics I find it surprising this effect hasn't been measured yet. What are the experimental difficulties (and ...
More Anonymous's user avatar
3 votes
1 answer
136 views

Can double copy address the weakness of gravity?

I hope I didn't miss a post that already answers this question. I am simply wondering if there is a natural framework in the double copy approach to explain the weakness of gravity? I don't require ...
FlatterMann's user avatar
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7 votes
3 answers
1k views

How can we determine the energy scale of a physics theory?

It is very common in physics, when we refer to the most diverse theories, on the most diverse length scales, we also refer to their energy scale. It is through the energy scale that we classify a ...
lucenalex's user avatar
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1 vote
2 answers
167 views

“Massive” v.s. “Supermassive” black holes

I think I understand what a black hole is. When there is enough mass in a given area the “bend” in time space approaches infinite (please correct me if this is wrong). I understand there are different ...
Everett's user avatar
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4 votes
3 answers
1k views

What exactly is order of magnitude?

I am little bit confused with what order of magnitude is. In my book it says, when we write approximate values of quantities in powers of ten i.e $10^b$, then $10^b$ is the order of magnitude. But ...
Daniel Joseph's user avatar
3 votes
1 answer
223 views

What does it mean that gravitation separated from the four forces at $10^{-36}$ seconds?

Physicists have used math to calculate that gravitation separated from the 4 forces at 10^-36 seconds after the big bang, which is even before the inflationary period. The universe was still smaller ...
foolishmuse's user avatar
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3 votes
2 answers
323 views

Is the exact definition of the Planck units important?

Wikipedia says there are other, possibly better ways to define the Planck Units based on whether we want to factor in or out a $2$ or a $\pi$ or a $4\pi$ as the case may be. Most of them represent ...
zucculent's user avatar
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1 vote
0 answers
111 views

Steady Couette flow where the moving wall suddenly stops

Let it be a planar Couette flow for an incompressible fluid with dynamic viscosity $\mu$ and density $\rho$ that has reached the steady-state. Assuming that the plates are placed at the $xz$ plane, ...
Invenietis's user avatar
1 vote
1 answer
41 views

Scaling difficulty of landing a rocket

I am wondering whether it is more difficult to land (as spaceX does) a rocket of height $k L$ than landing a rocket of height $L$? Is there some scaling law? Or at least is there a way to see in the ...
J.Mayol's user avatar
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2 answers
153 views

Why is $\exp(-1)$ a good benchmark in many physics? [closed]

In many subjects in Physics (not only phys though), we often encounter a value which gives $\exp(-1)$, such as a time constant in circuitry ($\exp(-t/RC)$, $t=RC$ gives $exp(-1)$), lifetime, mean free ...
Glen's user avatar
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14 votes
6 answers
3k views

Are neurons more energy efficient than transistors?

In terms of order of magnitude, how does a the energy consumption of a typical mammalian neuron (in the brain) compare with the state of the art MOSFET?
user1576720's user avatar
1 vote
2 answers
39 views

Explain the theory behind this problem(if possible using number line or graph or any other method of pictorial representation) [closed]

In a situation in which data are known to three significant digits, we write 6.379 m = 6.38 m and 6.374 = 6.37 m. When a number ends in 5, we arbitrarily choose to write 6.375 m = 6.38 m. We could ...
Deepak K R's user avatar
2 votes
0 answers
1k views

How many waves are in the ocean? [closed]

XKCD #2741 mentions in the title text It's cool how, when there's a number lots of people are curious about, but which isn't easy to measure, some random guess will get cited everywhere and become ...
Jacob Manaker's user avatar
0 votes
1 answer
529 views

Is it just a coincidence that the range of order of magnitude of length and time is $10^{41}$ does it have some explanation?

The ratio of the longest and shortest lengths of objects in our universe is about $10^{41}$. Interestingly enough, the ratio of the longest and shortest time intervals associated with the events and ...
user avatar
13 votes
3 answers
2k views

Comparing the strength of gravity and electricity

I often see and hear people claiming that "the gravitational force is much weaker than the electromagnetic force". Usually, they justify it by comparing the universal gravity constant to ...
ByoTic's user avatar
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6 votes
1 answer
87 views

How to incorporate HEP into the naive picture of QM?

When I explain QM to non-physicists, I sometimes say that quantum effects are typically noticeable on very small scales. For example, a QM particle in the harmonic potential behaves mostly classically,...
mavzolej's user avatar
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3 votes
1 answer
203 views

What is the smallest time that the current technology can measure?

Many physical phenomena are associated with unbelievably small time scales. Let me give a few examples. The time scale associated with visible light is $\sim$ a femtosecond ($10^{-15}$ sec), The ...
Solidification's user avatar
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0 answers
119 views

What is the value of electroweak scale? Depends on literature?

Depending on the literature, we see for the electroweak scale the following typical values : 100 GeV, 125 GeV (Higgs mass), 246 GeV (vev), 1 TeV So what is really the value of electroweak scale?
Mathieu Krisztian's user avatar
2 votes
2 answers
599 views

Order of magnitude of zero?

I was wondering what exactly the order of magnitude is of 0. Just by calculating it you obviously get $-\infty$ because of the logarithm but is this really correct?
Joppe De Jonghe's user avatar
0 votes
1 answer
881 views

What does the resistance of same order means in wheatstone bridge means?

As we know that in order to increase the sensitivity of wheat stone bridge resistance are of same order but here what exactly order means can anyone give me an example of this order?
mayank bisht's user avatar
0 votes
3 answers
1k views

Understanding importance of Planck energy

Planck length is considered to be smallest length possible in the universe. Planck time is smallest time interval possible. Similarly what is importance of Planck energy because it is neither ...
Mahesh's user avatar
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4 votes
2 answers
1k views

How do physicists compare the relative strengths of the four forces?

Since the four forces are different, with different force carriers, how are they (seemingly) directly compared? I often read that the weak force, for example, is many orders of magnitude stronger ...
Kurt Hikes's user avatar
  • 4,433
2 votes
2 answers
469 views

Nucleus vibration

What are the frequencies of the vibrations of the atom's nucleus? Is it in the quadrillions? Vibrating molecules is not the same thing - which is addressed as phonon vibration.
Art Snow 's user avatar
-2 votes
1 answer
66 views

Multiple levels of expansion of space? [closed]

It can easily be seen from the plot that there are at least 3 gaps between objects in the large, there is the gap between the planets and the moons, and between the planets and stars, and between ...
OzOz's user avatar
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1 vote
1 answer
71 views

Why is quantum gravity so tough to be proved experimentally?

A great deal of particle physics experiments are going on in CERN and similar experimental labs and their study is based on quantum field theory? But I could not understand why quantum gravity is so ...
JamesP's user avatar
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1 vote
1 answer
157 views

The answer to this question is not close to the age of the universe, then why do we say it is?

I saw this question in our textbook A great physicist of the century (P.A.M. Dirac) loved playing with numerical values of Fundamental constants of nature. This led him to an interesting ...
NxtGen's user avatar
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0 votes
2 answers
146 views

Why does everyone seem to assume that gravitational waves will always be very small? [duplicate]

The size or effective distortion field of a gravitational-wave perturbation at any given location in space-time is determined by the distance separating the source and that location. This describes a ...
debyton's user avatar
  • 47
-1 votes
1 answer
143 views

Order of magnitude radiation measures conversion?

Standard unit of ionizing radiation dose is Sievert. I can get a rough idea of how dangerous absorbing various amounts is from https://xkcd.com/radiation/ and other sources. There are many other ...
Max M's user avatar
  • 79
2 votes
1 answer
174 views

Why does the universe manifest scale?

I'll try outline my question in clear terms, articulating specific aspects that are its primary motivators. I'm just beginning in my exploration of physics as a student, but a persistent question that ...
Daniel C. Lucas's user avatar
-4 votes
2 answers
1k views

Why do people not have gravitational attraction? [closed]

Gravitational theory says every thing that has mass attract each other. So why don't people attract each other and overlap
user227045's user avatar
0 votes
2 answers
230 views

How do you calculate Reynolds and Mach's numbers before solving the Navier-Stokes equations?

Apologies in advance if the question is trivial. I am accustomed to electromagnetics but an amateur on fluid dynamics. My understanding is that the Navier-Stokes equations are solved to determined ...
Max_89's user avatar
  • 3
2 votes
1 answer
80 views

Sun's energy and grand unification

According to Wikipedia, The approximate grand unification energy value is equal to $1×10^{25}$ eV or $10^{16}$ GeV This is equal to $1602176$ J. Now, The Earth receives 174 petawatts (PW) ...
OmG's user avatar
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1 vote
2 answers
185 views

When is the order of magnitude not equal to the exponent of scientific notation?

Explain why the order of magnitude is sometimes not the same as the exponent in scientific notation. It is because of the units?
CountDOOKU's user avatar
1 vote
3 answers
205 views

Where is the line between Quantum and Relativity?

Its often said QM is for the very small and GR for the very large. This brings to mind that there should be some limit at which one starts to apply and the other stops. Now I know there are more ...
christo183's user avatar
2 votes
1 answer
186 views

Different approch on Order of magnitude confusion [closed]

My problem: How many orders of magnitude larger is the sun $(1.99$ x $10^{30} kg)$ than the moon $(7.32$ x $10^{22} kg)$. Justification 1: So according to my teacher, we can do this question by ...
CountDOOKU's user avatar
3 votes
2 answers
252 views

What is the point of generalizing a more specific result to an order of magnitude?

In my textbook, an example wants me to find an estimate of the number of cells in a human brain. It gives the volume of the brain as $8 \times 10^{-3}\ \rm m^3$ which it then estimates further as $...
MichaelFox's user avatar
26 votes
4 answers
17k views

If an apple is magnified to the size of the earth, then the atoms in the apple are approximately the size of the original apple

Quoting from the Feynman Lectures on Physics - Vol I: The atoms are 1 or $2 \times 10^{−8}\ \rm cm$ in radius. Now $10^{−8}\ \rm cm$ is called an angstrom (just as another name), so we say they are ...
Lone Learner's user avatar
-1 votes
1 answer
609 views

What would happen if gamma-ray burst from a supernova burst hit the sun? [closed]

What would happen if gamma-ray burst from a supernova burst hit the sun? Would the sun explode? Would the sun expand. Have a longer lifetime? Shorter Lifetime? Because people are nit-picky about stuff ...
yolo's user avatar
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0 votes
0 answers
121 views

Why are the Planck charge and Planck mass values so much larger than observed particles? [duplicate]

The Planck charge and mass values seem rather unusual. Is this an indicator that there is a lack of understanding in current theory, or is there a logical explanation for the magnitude of these two ...
user199479's user avatar
2 votes
1 answer
273 views

How much bigger is $a$ than $b$ when we write $a \gg b$?

When a condition of some physical quantity $a$ and $b$ is presented, say $a \gg b$, how much bigger do we say $a$ has to be than $b$? $10$ times? $1000$ times? $10^6$ times? Some context: I am ...
user avatar
2 votes
1 answer
66 views

How much faster is the chain reaction in a power plant than that of natural uranium ore? What about a nuclear bomb?

How much faster does the fissile uranium in a power plant 'break down' than an equivalent amount of naturally decaying U-235? How much faster is the chain reaction in a bomb compared to a power plant?...
Kurt Hikes's user avatar
  • 4,433
-3 votes
1 answer
153 views

Theory on how to break the speed of light [closed]

I am 14 years old and I think I have a good grasp on physics but I have a question. Imagine you were to shrink everything in the universe (except for yourself) down to the size of an atom and it was ...
Samuel carson's user avatar
2 votes
2 answers
216 views

Do you create gravitational waves by clapping your hands?

I was thinking that given that GW's can be created by the merger of both black holes and neutron stars I don't see why any two colliding objects wouldn't also be able to create gravitational waves, ...
Sam Cottle's user avatar
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1 vote
0 answers
61 views

Physical reason for light incoherence

In my physics notes it is stated that the light phase changes every 10^-8 seconds, hence light from 2 light original light sources. I understand how light from incoherent light doesn't allow for ...
raw_asparagus's user avatar