Timeline for How to understand $E=mc^2$?
Current License: CC BY-SA 4.0
14 events
| when toggle format | what | by | license | comment | |
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| May 9, 2022 at 9:05 | comment | added | m4r35n357 | @MichaelWalsby also there is no such thing as "resistance to acceleration" due to relativity. You can continue to accelerate as long as you have the fuel to do so! | |
| Jul 14, 2019 at 15:30 | comment | added | Alfred Centauri | @MichaelWalsby, keep in mind that if one accepts that the mass of an object increases with speed, one also accepts that the mass of the (relatively) moving object increases more in the direction of motion than in the directions orthogonal to the motion, i.e., $m_{||} \ne m_\perp$ | |
| Jul 14, 2019 at 15:06 | comment | added | MarianD | @Michael, your approach “Obsolete things are sometimes useful” is very common, but in this particular situation it's counter-productive as it prevent extirpation of such problematic, confusing term. Usefulness and correctness are two different things, and in physics is better IMHO to prefer the second one. See my edited answer. | |
| Jul 14, 2019 at 15:04 | history | edited | MarianD | CC BY-SA 4.0 |
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| Jul 14, 2019 at 14:37 | comment | added | Michael Walsby | Obsolete things are sometimes useful. You can be killed just as dead and at just as great a distance with a WW1 Lee Enfield .303 as with the most expensive modern rifle of similar calibre.. | |
| Jul 14, 2019 at 14:26 | comment | added | MarianD | @Michael, the increased momentum prevents a particle to achieving the speed of light. BTW it isn't my idea to avoid using the term “relativistic mass” — it's not so modern (about 50-year old) approach with roots in the recommendation of Einstein himself (in spite he used it in the beginning, but then he stopped and explained, why), so it will be better to argue with him :-) | |
| Jul 14, 2019 at 13:09 | comment | added | Michael Walsby | Marian, if relativistic mass increase doesn't exist, what is it which exerts the ever-increasing resistance to acceleration which prevents a particle from ever achieving the velocity of light in a vacuum? It's no good saying it's inertia - the inertia of what? As you say, everyone nowadays accepts that mass is a form of energy, which is why the masses of subatomic particles can be expressed in electron volts. | |
| Jul 14, 2019 at 12:30 | comment | added | Alfred Centauri | @Andy, $c$ is the invariant speed - an object with speed $c$ in one inertial frame of reference (IRF) has speed $c$ in all IRFs (by the Lorentz transformation). A such, the invariant speed $c$ is a universal 'conversion factor' between time and length. Since the Lorentz transformations 'mix' the dimensions of time and length, it shouldn't be surprising that the conversion factor $c$ is ubiquitous in relativistic expressions. | |
| Jul 14, 2019 at 12:04 | comment | added | Andy | @Aaron: thank you for a great phrase. I remember now that nothing can travel faster than light, but this phrase makes it much easier to remember. | |
| Jul 14, 2019 at 11:27 | comment | added | BioPhysicist | @Andy $c$ is more of "the speed limit of the universe", and photons happen to move at this speed. This speed is not unique to just light. | |
| Jul 14, 2019 at 11:20 | comment | added | Andy | Newtonian kinetic energy is E=1/2mv^2. My C is not lightspeed. It is just some unknown constant which I seek to find. Since E=mc^2 does not applies to photons why should the constant involve the speed of a photon at all? | |
| Jul 14, 2019 at 11:14 | comment | added | MarianD | The reason is that the formula for kinetic energy has the speed squared. | |
| Jul 14, 2019 at 11:03 | comment | added | Andy | Yes but why is the coefficient c^2 and not say pi? Is it possible to understand this using Einsteins box? If not how can I understand this? | |
| Jul 14, 2019 at 10:52 | history | answered | MarianD | CC BY-SA 4.0 |