A rough calculation or an approximation of the value, number, quantity, or extent of something so that it is usable for some purpose even if the input data may be incomplete or uncertain.
Questions tagged [estimation]
1205 questions
270
votes
5 answers
If I sliced the universe in half, would the slice go through a star?
This question is based on a discussion with a 10-year old. So if it is not clear how to interpret certain details, imagine how a 10-year old would interpret them.
This 10-year old does not know about relativistic issues, so assume that we are living…
user78574
141
votes
2 answers
How many photons are received per bit transmitted from Voyager 1?
As of 2024, according to https://voyager.jpl.nasa.gov/ , Voyager 1 is around one light·day away from Earth and still in radio contact. When Voyager 1 sends messages to Earth, roughly how many photons are (1) transmitted and (2) received per bit?
Craig Gidney
- 7,172
104
votes
4 answers
Would a pin head heated to 15 million degrees Celsius kill everyone in a 1000 mile radius?
The YouTube video How Hot Can it Get? contains, at the 2:33 mark, the following claim:
A pin head heated to 15 million degrees will kill everyone in a 1000 miles radius.
On what basis can this claim be true?
Some of the things I can think…
Jus12
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95
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If we had a "perfectly efficient" computer and all the energy in the Milky-way available, what number could it count to?
The idea for this question comes from an example in cryptography, where supposedly 256-bit symmetric keys will be enough for all time to come (brute-forcing a 256-bit key is sort-of equivalent to counting to $2^{255}$, with some constant in front of…
cooky451
- 1,069
95
votes
5 answers
Does a gun exert enough gravity on the bullet it fired to stop it?
My question is set in the following situation:
You have a completely empty universe without boundaries.
In this universe is a single gun which holds one bullet.
The gun fires the bullet and the recoil sends both flying in opposite directions.…
JadaLovelace
- 1,449
79
votes
8 answers
Does quantum mechanics play a role in the brain?
I'm interested in whether the scale of processes that occur in the brain is small enough to be affected by quantum mechanics. For instance, we ignore quantum mechanics when we analyze a game of tennis because a tennis ball is much too large to be…
QCD_IS_GOOD
- 7,145
76
votes
13 answers
If visible light has more energy than microwaves, why isn't visible light dangerous?
Light waves are a type of electromagnetic wave and they fall between 400-700 nm long. Microwaves are less energetic but seem to be more dangerous than visible light. Is visible light dangerous at all and why not?
suse
- 1,298
71
votes
3 answers
How big would my telescope have to be if I wanted to see the Mars rover from my backyard?
I imagine that with a big enough telescope, I would be able to zoom in and see the Mars rover in enough detail to make out the details (like the wheels, cameras, etc.). How large would the telescope have to be? (or how can I calculate this value?)
Josh
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Why isn’t CERN afraid of a fusion reaction in the LHC?
Given that they can reach terrifying energies and temperatures, why isn’t fusion of protons a concern? After all, they start with a plasma and ram protons into each other.
At some point the strong force will overcome the proton-proton electric…
aquagremlin
- 1,729
64
votes
6 answers
Why do we use capacitors and not batteries in defibrillator?
Why do we use capacitors in defibrillators and not batteries?
I know that capacitors are used to store electrical energy but isn't the function of a battery just the same?
Moreover, I know that batteries are used to make capacitors work in a…
musicinmyheart
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62
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11 answers
Why don't solar panels contribute to global warming?
I've been wondering this for a while but I have not yet encountered an explanation.
This is from my understanding of physics, which is by no means expert, so sorry for my crude explanation:
Energy within earth can be considered a closed system; it…
Joeri Hendrickx
- 731
59
votes
4 answers
How strong is the force of ice expanding when freezing?
Why does water contract on melting whereas gold, lead, etc. expand on melting? reminded me about something I've been wondering myself for some time.
We know that water expands as it freezes. The force is quite formidable - it can cause solid steel…
Vilx-
- 3,501
53
votes
5 answers
Freefall into snow
In the movie Frozen, the following dialogue takes place:
Anna: "It's a hundred-foot drop."
Kristoff: "It's two hundred."
Anna: "Okay, what if we fall?"
Kristoff: "There's 20 feet of fresh powder down there. It will be like landing on a pillow...…
user3932000
- 1,167
50
votes
4 answers
Could I survive at (or near) absolute zero with a very, very, very thick sweater?
Imagine I'm in an infinitely large vacuum and have a special apparatus built into my body that allows me to breath, eat, pee/poo, etc. and never age. The vacuum is similar to deep space and has no heat source or visible light and is therefore quite…
Behacad
- 607
49
votes
9 answers
Why is air not sucked off the Earth?
People said outside earth is a vacuum. But the air does not get sucked from the Earth's surface. Some said it is due to gravity and some said the speed of air molecules are not high enough to escape. We know vacuum will suck air like your vacuum…
Weidong Tong
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