All Questions

7k views

How can ants carry items much heavier than themselves?

This morning I saw an ant and suddenly a question came to my mind: how do ants actually carry items much heavier than themselves? What's the difference (in physics) between us and them?
7k views

Why didn't the Big Bang create heavy elements?

In the case of a supernova explosion it is possible to create heavy elements through fusion. Supernovae have a tremendous amount of energy in a very small volume but not as much energy per volume as ...
21k views

What Is Energy? Where did it come from?

The simplistic undergrad explanation aside. I've never really understood what energy really is. I've been told that it's something when converted from one kind of something to another kind does some ...
8k views

Why don't choir voices destructively interfere so that we can't hear them?

Sound is propagated by waves. Waves can interfere. Suppose there are two tenors standing next to each other and each singing a continuous middle-C. Will it be the case that some people in the ...
7k views

Will a blanket warm you if you are underwater?

Suppose a man falls into very cold water and gets their foot stuck under a heavy rock. Fortunately, his head is above water and someone is able to call for help. The paramedics want to keep him warm ...
13k views

Does gravity exist in a vacuum?

My understanding has always been that it does from conventional science courses, but really thinking about it, I was wondering if this is really the case. To my limited understanding there is a ...
39k views

Why does the atmosphere rotate along with the earth?

I was reading somewhere about a really cheap way of travelling: using balloons to get ourselves away from the surface of the earth. The idea held that because the earth rotates, we should be ...
3k views

Is temperature a Lorentz invariant in relativity?

If an observer starts moving at relativistic speeds will he observe the temperature of objects to change as compared to their rest temperatures? Suppose the rest temperature measured is $T$ and the ...
2k views

What causes insects to cast large shadows from where their feet are?

I recently stumbled upon this interesting image of a wasp, floating on water: Assuming this isn't photoshopped, I have a couple of questions: Why do you see its image like that (what's the ...
6k views

Why does dry spaghetti break into three pieces as opposed to only two?

You can try it with your own uncooked spaghetti if you want; it almost always breaks into three when you snap it. I am asking for a good physical theory on why this is along with evidence to back it ...
4k views

Is there a symmetry associated to the conservation of information?

Conservation of information seems to be a deep physical principle. For instance, Unitarity is a key concept in Quantum Mechanics and Quantum Field Theory. We may wonder if there is an underlying ...
10k views

Why is quantum entanglement considered to be an active link between particles?

From everything I've read about quantum mechanics and quantum entanglement phenomena, it's not obvious to me why quantum entanglement is considered to be an active link. That is, it's stated every ...
10k views

Moon's pull causes tides on far side of Earth: why?

I have always wondered and once I even got it, but then completely forgot. I understand that gravity causes high and low tides in oceans, but why does it occur on the other side of Earth?
9k views

A list of inconveniences between quantum mechanics and (general) relativity?

It is well known that quantum mechanics and (general) relativity do not fit well. I am wondering whether it is possible to make a list of contradictions or problems between them? E.g. relativity ...
5k views

Is there a small enough planet or asteroid you can orbit by jumping?

I just had this idea of orbiting a planet just by jumping and then flying upon it on its orbit kind of like superman. So, Would it be theoretically possible or is there a chance of that small body to ...
7k views

Can Maxwell's equations be derived from Coulomb's Law and Special Relativity?

As an exercise I sat down and derived the magnetic field produced by moving charges for a few contrived situations. I started out with Coulomb's Law and Special Relativity. For example, I derived the ...
20k views

Is it possible that there is a color our human eye can't see?

Is it possible that there's a color that our eye couldn't see? Like all of us are color blind to it. If there is, is it possible to detect/identify it?
13k views

How long can you survive 1 million degrees?

I asked my Dad this once when I was about 14, and he said that no matter how short the amount of time you were exposed to such a great temperature, you would surely die. The conversation went ...
2k views

Experimental test of the non-statisticality theorem?

Context: The paper On the reality of the quantum state (Nature Physics 8, 475–478 (2012) or arXiv:1111.3328) shows under suitable assumptions that the quantum state cannot be interpreted as a ...
4k views

Is there a way for an astronaut to rotate?

We know that if an imaginary astronaut is in the intergalactic (no external forces) and has an initial velocity zero, then he has is no way to change the position of his center of mass. The law of ...
4k views

How to measure the wavelength of a laser pointer?

I'm working on something and I need to know the wavelength of the laser pointer that I'm using. Can you suggest me a way, using some optics formulae, or anything else to calculate the wavelength?
18k views

Does centrifugal force exist?

Currently in my last year of high school, and I have always been told that centrifugal force does not exist by my physics teachers. Today my girlfriend in the year below asked me what centrifugal ...
5k views

Why did Feynman's thesis almost work?

A bit of background helps frame this question. The question itself is in the last sentence. For his PhD thesis, Richard Feynman and his thesis adviser John Archibald Wheeler devised an astonishingly ...
6k views

Why is the Sun almost perfectly spherical?

Relatively recent measurements indicate that the Sun is nearly the roundest object ever measured. If scaled to the size of a beach ball, it would be so round that the difference between the widest ...
22k views

Proof that the Earth rotates?

What is the proof, without leaving the Earth, and involving only basic physics, that the earth rotates around its axis? By basic physics I mean the physics that the early physicists must've used to ...
7k views

Why do atomic clocks only use caesium?

Modern atomic clocks only use caesium atoms as oscillators. Why don't we use other atoms for this role?
10k views

Quantum Field Theory from a mathematical point of view

I'm a student of mathematics with not much background in physics. I'm interested in learning Quantum field theory from a mathematical point of view. Are there any good books or other reference ...
6k views

Can a Skydiver Land On a Large Slide and Survive?

Please forgive my lack of artistic ability, but here's my question: Consider that a skydiver, without using his parachute, were to fall exactly parallel to a giant curved slide that starts at ...
9k views

What's the point of Hamiltonian mechanics?

I've just finished a Classical Mechanics course, and looking back on it some things are not quite clear. In the first half we covered the Lagrangian formalism, which I thought was pretty cool. I ...
5k views

Do solar systems typically spin in the same direction as their galaxy?

Is the net angular momentum vector of our solar system pointing in roughly the same direction as the Milky Way galaxy's net angular momentum vector? If yes or no, is that common for most stars in the ...
4k views

How small does sand have to be to get wet?

I think of sand as a lot of very small rocks. Suppose I have a pile of rocks, each about 1cm in size, and the pile is a meter tall. If I pour a bucket of water on the rocks, most of the water will ...
13k views

How long a straw could Superman use?

To suck water through a straw, you create a partial vacuum in your lungs. Water rises through the straw until the pressure in the straw at the water level equals atmospheric pressure. This ...
5k views

Is it possible to “see” atoms?

As per my knowledge, atoms are small beyond our imaginations. But there is an image on Wikipedia that shows silicon atoms observed at the surface of silicon carbide crystals. The image: How can we ...
6k views

If dark matter only interacts with gravity, why doesn't it all clump together in a single point?

I'm a complete layperson. As I understand, dark matter theoretically only interacts with the gravitational force, and doesn't interact with the other three fundamental forces: weak nuclear force, ...
6k views

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 ...
4k views

What is information?

We're all familiar with basic tenets such as "information cannot be transmitted faster than light" and ideas such as information conservation in scenarios like Hawking radiation (and in general, ...
8k views

What is spin as it relates to subatomic particles?

I often hear about subatomic particles having a property called "spin" but also that it doesn't actually relate to spinning about an axis like you would think. Which particles have spin? What does ...
6k views

What justifies dimensional analysis?

Dimensional analysis, and the notion that quantities with different units cannot be equal, is often used to justify very specific arguments, for example, you might use it to argue that a particular ...
8k views

Why is water clear?

Water appears transparent to visible light, yet most other objects are opaque. Why is that? Is there an explanation why water appears transparent? Is water transparent at all wavelengths, or are ...
12k views

Why does a window become a mirror at night?

In day, when you look in the room through the window out, you can clearly see what happens outside. At night when it's dark outside but there's light inside you can look in the window but it becomes a ...
3k views

What happened to David John Candlin?

This is an ultra-soft question about relatively recent history. While reading some of Mandelstam's papers, I noticed that he cites David John Candlin consistenly whenever he does anything with ...
14k views

Why does a candle blow out when we blow on it? Our breath is 16% oxygen and only 4% CO2

Don't say that a layer of carbon dioxide covers the flame, because our breath has more oxygen than carbon dioxide. Also, our breath does not cool the flame as it is itself warm. So what is happening ...
5k views

Why isn't length contraction permanent even though time dilation is?

It's my understanding that when something is going near the speed of light in reference to an observer, time dilation occurs and time goes slower for that fast-moving object. However, when that ...
5k views

Why does a cup with 100 g water float when placed on another cup with 50 g of water?

Imagine we have cup A with 50 g of water and cup B (smaller in width than A) with 100 g of water. Now put cup B into cup A. If the width of both cups are of comparable size then the cup with ...
4k views

Is there something similar to Noether's theorem for discrete symmetries?

Noether's theorem states that, for every continuous symmetry of an action, there exists a conserved quantity, e.g. energy conservation for time invariance, charge conservation for $U(1)$. Is there any ...
7k views

Dimensionless Constants in Physics

Forgive me if this topic is too much in the realm of philosophy. John Baez has an interesting perspective on the relative importance of dimensionless constants, which he calls fundamental like alpha, ...
3k views

Do all black holes have a singularity?

If a large star goes supernova, but not enough mass collapses to form a black hole, it often forms a neutron star. My understanding is that this is the densest object that can exist because of the ...
3k views

Intuitively, why are bundles so important in Physics?

I've seem the notion of bundles, fiber bundles, connections on bundles and so on being used in many different places on Physics. Now, in mathematics a bundle is introduced to generalize the ...
21k views

What happens to the energy when waves perfectly cancel each other?

What happens to the energy when waves perfectly cancel each other (destructive interference)? It appears that the energy "disappear" but the law of conservation of energy states that it can't be ...
2k views

Why does our voice sound different on inhaling helium?

This question (and answer) is an attempt to clear the air on what appears to be a very simple issue, with conflicting or unclear explanations on the internet. Arguments, negations, etc are invited. ...

15 30 50 per page