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1500 questions
154
votes
2 answers
Does the Planck scale imply that spacetime is discrete?
On a quantum scale the smallest unit is the Planck scale, which is a discrete measure.
There several question that come to mind:
Does that mean that particles can only live in a discrete grid-like structure, i.e. have to "magically" jump from one…
vonjd
- 3,801
154
votes
8 answers
Why is nuclear waste more dangerous than the original nuclear fuel?
I know the spent fuel is still radioactive. But it has to be more stable than what was put in and thus safer than the uranium that we started with. That is to say, is storage of the waste such a big deal? If I mine the uranium, use it, and then bury…
Anthony B
- 1,493
153
votes
13 answers
Is time continuous or discrete?
I was coding a physics simulation, and noticed that I was using discrete time. That is, there was an update mechanism advancing the simulation for a fixed amount of time repeatedly, emulating a changing system.
I though that was interesting, and now…
jcora
- 2,139
153
votes
2 answers
Why does a mirror split my laser beam?
Last night my daughter was asking why a mirror "always does that" (referring to reflecting a spot of light). To help her figure it out, I grabbed my green laser pointer so she could see the light traveling from the source and reflecting off the…
Wayne Werner
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150
votes
7 answers
Why do people categorically dismiss some simple quantum models?
Deterministic models. Clarification of the question:
The problem with these blogs is that people are inclined to start yelling at each other. (I admit, I got infected and it's difficult not to raise one's electronic voice.) I want to ask my question…
G. 't Hooft
- 5,521
150
votes
10 answers
Why is my hand not burned by the air in an oven at 200 °C?
I have this problem from University Physics with Modern Physics (13th Edition):
The inside of an oven is at a temperature of 200 °C (392 °F). You can put your hand in the oven without injury as long as you don't touch anything. But since the air…
InfZero
- 1,493
147
votes
8 answers
Why does a remote car key work when held to your head/body?
I was trying to unlock my car with a keyfob, but I was out of range. A friend of mine said that I have to hold the transmitter next to my head. It worked, so I tried the following later that day:
Walked away from the car until I was out of…
Yababaa
- 2,269
146
votes
7 answers
Why doesn't water boil in the oven?
I put a pot of water in the oven at $\mathrm{500^\circ F}$ ($\mathrm{260^\circ C}$ , $\mathrm{533 K}$). Over time most of the water evaporated away but it never boiled. Why doesn't it boil?
Hovercouch
- 1,451
146
votes
3 answers
Why are the windows of bridges of ships always inclined?
What is the reason that the windows of ships' bridges are always inclined as shown in the above picture?
veronika
- 2,867
146
votes
15 answers
What happens to the energy when waves perfectly cancel each other?
What happens to the energy when waves completely cancel each other out via destructive interference? It seems like the energy just disappears, but that would violate the law of energy conservation.
My guess is that the kinetic energy is transformed…
aortizmena
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144
votes
6 answers
If you view the Earth from far enough away can you observe its past?
From my understanding of light, you are always looking into the past based on how much time it takes the light to reach you from what you are observing.
For example when you see a star burn out, if the star was 5 light years away then the star…
JD Isaacks
- 1,863
143
votes
24 answers
How do I experimentally measure the surface area of a rock?
I hope this is the right place to ask this question.
Suppose I found a small irregular shaped rock, and I wish to find the surface area of the rock experimentally. Unlike for volume, where I can simply use Archimedes principle, I cannot think of a…
Pritt Balagopal
- 3,237
142
votes
11 answers
How fast does gravity propagate?
A thought experiment: Imagine the Sun is suddenly removed. We wouldn't notice a difference for 8 minutes, because that's how long light takes to get from the Sun's surface to Earth.
However, what about the Sun's gravitational effect? If gravity…
Stefano Borini
- 3,970
142
votes
13 answers
Is anti-matter matter going backwards in time?
Some sources describe antimatter as just like normal matter, but "going backwards in time". What does that really mean? Is that a good analogy in general, and can it be made mathematically precise? Physically, how could something move backwards in…
Gerard
- 7,189
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