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1500 questions
193
votes
21 answers
Given Newton's third law, why are things capable of moving?
Given Newton's third law, why is there motion at all? Should not all forces even themselves out, so nothing moves at all?
When I push a table using my finger, the table applies the same force onto my finger like my finger does on the table just with…
user16458
- 1,973
192
votes
15 answers
Why does space expansion not expand matter?
I have looked at other questions on this site (e.g. "why does space expansion affect matter") but can't find the answer I am looking for.
So here is my question: One often hears talk of space expanding when we talk about the speed of galaxies…
SoulmanZ
- 2,035
190
votes
5 answers
Why is Google's quantum supremacy experiment impressive?
In the Nature paper published by Google, they say,
To demonstrate quantum supremacy, we compare our quantum processor against state-of-the-art classical computers in the task of sampling the output of a pseudo-random quantum circuit. Random…
Bridgeburners
- 2,046
186
votes
2 answers
Why do we not have spin greater than 2?
It is commonly asserted that no consistent, interacting quantum field theory can be constructed with fields that have spin greater than 2 (possibly with some allusion to renormalization). I've also seen (see Bailin and Love, Supersymmetry) that we…
James
- 2,851
182
votes
8 answers
Why do shadows from the sun join each other when near enough?
I was laying on my bed, reading a book when the sun shone through the windows on my left. I happened to look at the wall on my right and noticed this very strange effect. The shadow of my elbow, when near the pages of the book, joined up with the…
turnip
- 3,648
182
votes
5 answers
Gauge symmetry is not a symmetry?
I have read before in one of Seiberg's articles something like, that gauge symmetry is not a symmetry but a redundancy in our description, by introducing fake degrees of freedom to facilitate calculations.
Regarding this I have a few questions:
Why…
Revo
- 16,956
179
votes
7 answers
Why do we actually see the sun?
I haven't yet gotten a good answer to this: If you have two rays of light of the same wavelength and polarization (just to make it simple for now, but it easily generalizes to any range and all polarizations) meet at a point such that they're 180…
user22862
179
votes
2 answers
When separating an Oreo cookie, why does the cream stick to just one side only?
There is probably some reason for this, but I can't figure out what it is. I agree that it probably doesn't happen 100% of the time, but most all of the time, the cream is clinging to just one of the cookie sides.
Jiminion
- 2,639
179
votes
14 answers
Why does holding something up cost energy while no work is being done?
I read the definition of work as
$$W ~=~ \vec{F} \cdot \vec{d}$$
$$\text{ Work = (Force) $\cdot$ (Distance)}.$$
If a book is there on the table, no work is done as no distance is covered. If I hold up a book in my hand and my arm is stretched,…
SMUsamaShah
- 5,307
179
votes
3 answers
How does a knife cut things at the atomic level?
As the title says. It is common sense that sharp things cut, but how do they work at the atomical level?
wtoh
- 2,037
177
votes
1 answer
Why does NASA use gold foil on equipment and gold-coated visors?
I've read several websites about equipment covered with gold foil and astronaut helmet visors are coated with gold. However, their explanations are devoid of almost all physics content. Can someone explain the basic concept of why gold foil is so…
Smith
- 1,593
177
votes
21 answers
How do you make more precise instruments while only using less precise instruments?
I'm not sure where this question should go, but I think this site is as good as any.
When humankind started out, all we had was sticks and stones. Today we have electron microscopes, gigapixel cameras and atomic clocks. These instruments are many…
Vilx-
- 3,081
- 4
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- 22
171
votes
15 answers
What is a field, really?
There was a reason why I constantly failed physics at school and university, and that reason was, apart from the fact I was immensely lazy, that I mentally refused to "believe" more advanced stuff until I understand the fundamentals (which I,…
Dan
- 1,869
170
votes
2 answers
Why do sunbeams diverge even though the sun is much more than a few kilometers away?
Consider this picture of sun beams streaming onto the valley through the clouds.
Given that the valley is only (at a guess) 3km wide, with simple trigonometry and the angles of the beams, this gives the result that the position of the light source…
user56903
168
votes
2 answers
Why is my dryer radioactive?
My Geiger counter measures a background radiation level in my home of 0.09–0.11 μSv/h.
When I stick it inside the dryer right after it finishes a cycle (while the clothes are still inside), it registers a radiation level of 0.16–0.18 μSv/h.
What…
Marsroverr
- 863