# What is Existence: Definition and 570 Discussions

Existence is the ability of an entity to interact with physical or mental reality. In philosophy, it refers to the ontological property of being.

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1. ### I If we had a TOE, would we be able to explain why there is something rather than nothing?

If we could have one day theory of everything thing, would we be able to explain why there is something rather than nothing and would we be able to know why there are physical laws?

7. ### Exploring the Origins and Diversity of Life in the Universe

Flipboard, Big Think URL, Astro-Physics interest.
8. ### I Integrity of matter / space and time

I have probably a basic question from Space, Time and Matter area. My 11 years old daughter asked me once why we exist physically in a stable form if everything is infinite. We had a conversation about it but then it got me thinking about this and it seems I can't find the answer. There is...
9. ### I Biphoton: Existence of layered or multiple entanglements

I read this recent article describing photon quantum entanglement to produce higher resolution microscope. https://phys.org/news/2023-05-quantum-entanglement-photons-microscope-resolution.html I am curious if quantum entanglement could exist in layers with a third or more entanglement feature...
10. ### I Proof of Lorentz Gauge Existence: Help Understanding Schutz 8.3

In Schutz 8.3, while proving that a Lorentz gauge exists, it is stated that $$\bar h^{(new)}_{\mu\nu} = \bar h^{(old)}_{\mu\nu} - \xi_{\mu,\nu} - \xi_{\nu,\mu} + \eta_{\mu\nu}\xi^\alpha_{,\alpha}$$ where ##\bar h## is the trace reverse and ##\xi^\alpha## are the gauge functions. Then it follows...
11. ### A Extended Wigner’s Friend Scenario and the existence of the reality

https://backreaction.blogspot.com/2022/02/has-quantum-mechanics-proved-that.html It is unclear for me, why from these experiments the tabloids made the conclusion that "the reality does not exist"? Does the essence of this experiment lie in the fact that it confirmed the Wigner's friend...
12. ### I Existence and Uniqueness of Inverses

Existence: Ax = b has at least 1 solution x for every b if and only if the columns span Rm. I don't understand why then A has a right inverse C such that AC = I, and why this is only possible if m≤n. Uniqueness: Ax = b has at most 1 solution x for every b if and only if the columns are...
13. ### Proving that the inverse of a rational number exists

Problem statement : I cope and paste the problem as it appears in the text below. Attempt : Not being a math student, I try and prove the above statement using an "intuitive" way. Let us have a rational number ##b = \frac{n}{m}##. Multiplying with ##a## from the right, we see ##ab =...
14. ### B Proof of the existence of atoms

It is said that some physicists doubted the existence of atoms in 1900 until Einstein proved their existence a few years later. Did Mendeleev's creation of the periodic table in the 1870s already prove the reality of atoms by giving the known elements atomic masses?
15. ### A Does the existence of a POVM require an ancilla?

In DeMuynck's paper, POVMs: a small but important step beyond standard quantum mechanics, he describes a "generalized quantum mechanics" in which a generalized observable can be represented by POVM. In contrast, most other references that I have seen discussing this talk about first...
16. ### A Existence of unique solutions to a first order ODE on this interval

I am trying to find a way to prove that a certain first order ode has a unique solution on the interval (1,infinity). Usually the way to do this is to show that if x' = f(t,x) (derivative with respect to t), then f(t,x) and the partial derivative with respect to f are continuous. However, this...
17. ### B Another proof of the existence of extreme values on open intervals

Hello, PF This is Theorem 8 of Chapter 4 of the ninth edition of Calculus, by Robert A. Adams: "Existence of extreme values on open intervals". I have an alternative and easier proof, based on epsilon-delta arguments, but it's not mine, and I don't understand it completely. The fact is that...
18. ### DP: proving existence of optimal substructure for "Sherlock and Cost"

I was attempting to solve the "Sherlock and Cost" problem from HackerRank using DP: But before I went to come up with a recursive relation, I wanted to find if the problem possesses an optimal substructure, and I was following these steps as written at CLRS book: Mentor note: Inline images of...
19. ### I Evidence for existence of a 9th Planet in the solar system

Could the existence of the 9th planet of the solar system is possible under these arguments of existence of it some where in the out scurt of solar system? The evidence for Planet 9 comes from its gravitational pull on other bodies. If the planet exists, its gravity will affect the orbits of...
20. ### I Is the existence of a Dyson Sphere impossible?

Specifically a monolithic Dyson Sphere; also, how would a Dyson Swarm work / be a better option?

38. ### B Existence of parallels in axiomatic plane geometries

Parallels exist in both Euclidean and Hyperbolic geometry. Yet each includes a separate postulate that declares the number of parallels to a line in a plane through a given point. But it seems that if both geometries have parallels then their existence - as opposed to how many of them - should...
39. ### I Riemann Integration ... Existence Result .... Browder, Theorem 5.12 ....

I am reading Andrew Browder's book: "Mathematical Analysis: An Introduction" ... ... I am currently reading Chapter 5: The Riemann Integral and am currently focused on Section 5.2 Existence Results ... ... I need some help in understanding the proof of Theorem 5.12 ...Theorem 5.12 and its...
40. ### MHB Riemann Integration ... Existence Result .... Browder, Theorem 5.12 ....

I am reading Andrew Browder's book: "Mathematical Analysis: An Introduction" ... ... I am currently reading Chapter 5: The Riemann Integral and am currently focused on Section 5.2 Existence Results ... ... I need some help in understanding the proof of Theorem 5.12 ...Theorem 5.12 and its...
41. ### B Unraveling the Tachyon and Photon Debate: Exploring Faster-Than-Light Particles

A tachyon or tachyonic particle is a hypothetical particle that always travels faster than light. Most physicists believe that faster-than-light particles cannot exist because they are not consistent with the known laws of physics. - Tachyon definition The photon is a type of elementary...
42. ### I On what plane of existence do quantum computations occur?

I was recommended by another mentor to purchase a good book on MWI, which I think should be a thread or poll of its own. Anyway, I might have debased myself too much in that other topic, as I understand on an abstract level how QM works. In my own words, I feel as though possible worlds are...
43. ### B What parameters of physics are most important to the existence of life?

The universe after the big event was a lot of lifeless stuff. However, as things settled down the rules behind the curtain were such that life was allowed to develop, they may have even been such that they encouraged the things to happen that were conducive to the process that has resulted in...
44. ### Chemistry Calculating Hybridisation and Existence of a Compound with Boron

One would easily calculate its hybridisation by the above formula which comes out to be sp. But my doubt is that will the compound even exist?As boron will become electron deficient and how we will calculate no. of bond pairs and lone pairs.Please clear my doubt.
45. ### A Exploring the Existence of Baryons with Positive Strangeness

Hi all, I read on "Intoduction to Elementary Particle Physics" (A. Bettini) that baryons with positive strangeness cannot exist. I don't know what to conclude from this sentence: sigma-baryons have negative strangeness, since there's a sigma as valence quark. But these baryons have, of course...
46. ### A Does Bohmian Mechanics yield the existence of a multiverse?

David Deutsch, a theoretical physicist, talks about David Bohm in his book "the Fabric of Reality": "[w]orking out what Bohm’s invisible wave will do requires the same computations as working out what trillions of shadow photons will do. Some parts of the wave describe us, the observers...
47. ### I Are existence proofs outlawed in multi-valued logics?

First, is my assumption that all consistent multi-valued logics obey the principle of explosion from a false proposition correct? If so, how would one prove that? (I assume it is, because if not, then by the definition of intuitionist logic by Wolfram Mathworld...
48. ### A Why the fine-tuning argument for improbable existence is a fallacy

"In 1961, physicist Robert H. Dicke claimed that certain forces in physics, such as gravity and electromagnetism, must be perfectly fine-tuned for life to exist anywhere in the universe. Fred Hoyle also argued for a fine-tuned universe in his 1984 book Intelligent Universe. Much as been written...
49. ### I Conserved Stress-Energy in Gravitational Theories

My post https://www.physicsforums.com/threads/indirectly-coupling-gravitational-field-wei-tou-ni-stress-energy.969033/ got no replies. So I formulated those statements on the stress-energy tensor (SET) which are of most interest to me. I would be very grateful if you either confirmed them or...
50. ### I Invariant symbol implies existence of singlet representation

I don't understand what the last paragraph of the attached page means. Why does the Kronecker delta being an invariant symbol mean that the product of a representation R and its complex conjugate representation has the singlet representation with all matrices being zero? Doesn't the number...