Can the surface of a 3-dimension cube be diffeomorphic to a 3-dimension sphere?
We all know the surface of a cube homeomorphic to a sphere $S^3$ by retraction, but I'm confused that whether the surface of a cube can be diffeomorphic to $S^3$.
smooth-manifolds
add a comment |
We all know the surface of a cube homeomorphic to a sphere $S^3$ by retraction, but I'm confused that whether the surface of a cube can be diffeomorphic to $S^3$.
smooth-manifolds
Do you mean the surface of the unit hypercube in $Bbb R^4$, with the differential structure inherited from $Bbb R^4$? I don't really know what happens at the edges and vertices there, but it looks messy.
– Arthur
Dec 2 '18 at 14:51
Can you define what you mean by "3-dimensional cube" and by "3-dimensional sphere"? I would think that the former is the three-fold product of the unit interval, and the latter is the unit sphere in $Bbb R^4$. But those two spaces are not homeomorphic (e.g. their homology distinguishes them).
– Danu
Dec 2 '18 at 15:34
I think you mean a $3$ dimensional ball, which is a solid object like the earth. We use sphere to represent the surface of a ball.
– Ross Millikan
Dec 2 '18 at 16:07
In addition, in order to ask if two things are diffeomorphic, both things must be smooth manifolds. So, you must first choose some kind of atlas on the cube.
– Jason DeVito
Dec 4 '18 at 14:24
So the question is, if there exist a kind of atlas on cube, such that the cube with the atlas can be a smooth manifolds.
– Lau
Dec 4 '18 at 14:26
add a comment |
We all know the surface of a cube homeomorphic to a sphere $S^3$ by retraction, but I'm confused that whether the surface of a cube can be diffeomorphic to $S^3$.
smooth-manifolds
We all know the surface of a cube homeomorphic to a sphere $S^3$ by retraction, but I'm confused that whether the surface of a cube can be diffeomorphic to $S^3$.
smooth-manifolds
smooth-manifolds
edited Dec 4 '18 at 14:27
asked Dec 2 '18 at 14:35
Lau
541315
541315
Do you mean the surface of the unit hypercube in $Bbb R^4$, with the differential structure inherited from $Bbb R^4$? I don't really know what happens at the edges and vertices there, but it looks messy.
– Arthur
Dec 2 '18 at 14:51
Can you define what you mean by "3-dimensional cube" and by "3-dimensional sphere"? I would think that the former is the three-fold product of the unit interval, and the latter is the unit sphere in $Bbb R^4$. But those two spaces are not homeomorphic (e.g. their homology distinguishes them).
– Danu
Dec 2 '18 at 15:34
I think you mean a $3$ dimensional ball, which is a solid object like the earth. We use sphere to represent the surface of a ball.
– Ross Millikan
Dec 2 '18 at 16:07
In addition, in order to ask if two things are diffeomorphic, both things must be smooth manifolds. So, you must first choose some kind of atlas on the cube.
– Jason DeVito
Dec 4 '18 at 14:24
So the question is, if there exist a kind of atlas on cube, such that the cube with the atlas can be a smooth manifolds.
– Lau
Dec 4 '18 at 14:26
add a comment |
Do you mean the surface of the unit hypercube in $Bbb R^4$, with the differential structure inherited from $Bbb R^4$? I don't really know what happens at the edges and vertices there, but it looks messy.
– Arthur
Dec 2 '18 at 14:51
Can you define what you mean by "3-dimensional cube" and by "3-dimensional sphere"? I would think that the former is the three-fold product of the unit interval, and the latter is the unit sphere in $Bbb R^4$. But those two spaces are not homeomorphic (e.g. their homology distinguishes them).
– Danu
Dec 2 '18 at 15:34
I think you mean a $3$ dimensional ball, which is a solid object like the earth. We use sphere to represent the surface of a ball.
– Ross Millikan
Dec 2 '18 at 16:07
In addition, in order to ask if two things are diffeomorphic, both things must be smooth manifolds. So, you must first choose some kind of atlas on the cube.
– Jason DeVito
Dec 4 '18 at 14:24
So the question is, if there exist a kind of atlas on cube, such that the cube with the atlas can be a smooth manifolds.
– Lau
Dec 4 '18 at 14:26
Do you mean the surface of the unit hypercube in $Bbb R^4$, with the differential structure inherited from $Bbb R^4$? I don't really know what happens at the edges and vertices there, but it looks messy.
– Arthur
Dec 2 '18 at 14:51
Do you mean the surface of the unit hypercube in $Bbb R^4$, with the differential structure inherited from $Bbb R^4$? I don't really know what happens at the edges and vertices there, but it looks messy.
– Arthur
Dec 2 '18 at 14:51
Can you define what you mean by "3-dimensional cube" and by "3-dimensional sphere"? I would think that the former is the three-fold product of the unit interval, and the latter is the unit sphere in $Bbb R^4$. But those two spaces are not homeomorphic (e.g. their homology distinguishes them).
– Danu
Dec 2 '18 at 15:34
Can you define what you mean by "3-dimensional cube" and by "3-dimensional sphere"? I would think that the former is the three-fold product of the unit interval, and the latter is the unit sphere in $Bbb R^4$. But those two spaces are not homeomorphic (e.g. their homology distinguishes them).
– Danu
Dec 2 '18 at 15:34
I think you mean a $3$ dimensional ball, which is a solid object like the earth. We use sphere to represent the surface of a ball.
– Ross Millikan
Dec 2 '18 at 16:07
I think you mean a $3$ dimensional ball, which is a solid object like the earth. We use sphere to represent the surface of a ball.
– Ross Millikan
Dec 2 '18 at 16:07
In addition, in order to ask if two things are diffeomorphic, both things must be smooth manifolds. So, you must first choose some kind of atlas on the cube.
– Jason DeVito
Dec 4 '18 at 14:24
In addition, in order to ask if two things are diffeomorphic, both things must be smooth manifolds. So, you must first choose some kind of atlas on the cube.
– Jason DeVito
Dec 4 '18 at 14:24
So the question is, if there exist a kind of atlas on cube, such that the cube with the atlas can be a smooth manifolds.
– Lau
Dec 4 '18 at 14:26
So the question is, if there exist a kind of atlas on cube, such that the cube with the atlas can be a smooth manifolds.
– Lau
Dec 4 '18 at 14:26
add a comment |
1 Answer
1
active
oldest
votes
Let me answer this in lower dimensions:
First, consider the bi-unit square $S$ (the boundary of $[-1, 1] times [-1, 1]$ in $Bbb R^2$) and the unit circle $C$ in $Bbb R^2$.
There's a nice map ("radial projection") from the first to the second defined as follows:
$$
f(x, y) = begin{cases}
(frac{x}{sqrt{y^2+1}}, frac{y}{sqrt{y^2 + 1}})& x = pm 1 \
(frac{x}{sqrt{x^2+1}}, frac{y}{sqrt{x^2 + 1}})& y = pm 1 \
end{cases}
$$
which cane be written, more generally, as $f(x, y) = frac{1}{sqrt{x^2 + y^2}} (x, y)$, but I wanted to emphasize that it's defined on the square, and that at the four corners, the expressions involved shift from a dependence on $x$ to a dependence on $y$ or vice versa.
The inverse of $f$ is
$$
g(x, y) = begin{cases}
(frac{x}{|x|}, frac{y}{|x|}) & |x| ge |y|\
(frac{x}{|y|}, frac{y}{|y|}) & |x| le |y|
end{cases}
$$
Now one smoothness structure on $S$ can be described as follows: we say that a function
$$
u: S to Bbb R
$$ is smooth if and only iff
$$
u circ g : C to Bbb R
$$
is smooth.
With this definition, the square $S$ is a smooth manifold, and it's diffeomorphic to the circle $C$, with $g$ being the diffeomorphism.
There's a small caveat here, though: the inclusion map
$$
i : S to Bbb R^2: (x, y) mapsto (x, y)
$$
that embeds the square in the plane is not a smooth embedding.
What about higher dimensions? Well, an exact analog to $f$ can be written using more variables (and the "general" formula that I gave after the "cases" formula); the analog of $g$ involves 3 cases for a cube in 3-space (look at $|x|, |y|, |z|$: each case handles the situations where one of these is the largest).
When we get to 4-space, it's the same deal, but with another variable, and the formula for $g$ has four cases.
But everything else I said (including the fact that with the resulting smoothness structure, the standard embedding of the square/cube/hypercube is not a smooth embedding) remains true.
what's $s$ in $scirc g$?
– Lau
Dec 5 '18 at 3:16
Fixed. It's "u" -- just a typo. Sorry about that.
– John Hughes
Dec 5 '18 at 12:44
I think I have got your point, thanks a lot.
– Lau
Dec 5 '18 at 12:47
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3022708%2fcan-the-surface-of-a-3-dimension-cube-be-diffeomorphic-to-a-3-dimension-sphere%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Let me answer this in lower dimensions:
First, consider the bi-unit square $S$ (the boundary of $[-1, 1] times [-1, 1]$ in $Bbb R^2$) and the unit circle $C$ in $Bbb R^2$.
There's a nice map ("radial projection") from the first to the second defined as follows:
$$
f(x, y) = begin{cases}
(frac{x}{sqrt{y^2+1}}, frac{y}{sqrt{y^2 + 1}})& x = pm 1 \
(frac{x}{sqrt{x^2+1}}, frac{y}{sqrt{x^2 + 1}})& y = pm 1 \
end{cases}
$$
which cane be written, more generally, as $f(x, y) = frac{1}{sqrt{x^2 + y^2}} (x, y)$, but I wanted to emphasize that it's defined on the square, and that at the four corners, the expressions involved shift from a dependence on $x$ to a dependence on $y$ or vice versa.
The inverse of $f$ is
$$
g(x, y) = begin{cases}
(frac{x}{|x|}, frac{y}{|x|}) & |x| ge |y|\
(frac{x}{|y|}, frac{y}{|y|}) & |x| le |y|
end{cases}
$$
Now one smoothness structure on $S$ can be described as follows: we say that a function
$$
u: S to Bbb R
$$ is smooth if and only iff
$$
u circ g : C to Bbb R
$$
is smooth.
With this definition, the square $S$ is a smooth manifold, and it's diffeomorphic to the circle $C$, with $g$ being the diffeomorphism.
There's a small caveat here, though: the inclusion map
$$
i : S to Bbb R^2: (x, y) mapsto (x, y)
$$
that embeds the square in the plane is not a smooth embedding.
What about higher dimensions? Well, an exact analog to $f$ can be written using more variables (and the "general" formula that I gave after the "cases" formula); the analog of $g$ involves 3 cases for a cube in 3-space (look at $|x|, |y|, |z|$: each case handles the situations where one of these is the largest).
When we get to 4-space, it's the same deal, but with another variable, and the formula for $g$ has four cases.
But everything else I said (including the fact that with the resulting smoothness structure, the standard embedding of the square/cube/hypercube is not a smooth embedding) remains true.
what's $s$ in $scirc g$?
– Lau
Dec 5 '18 at 3:16
Fixed. It's "u" -- just a typo. Sorry about that.
– John Hughes
Dec 5 '18 at 12:44
I think I have got your point, thanks a lot.
– Lau
Dec 5 '18 at 12:47
add a comment |
Let me answer this in lower dimensions:
First, consider the bi-unit square $S$ (the boundary of $[-1, 1] times [-1, 1]$ in $Bbb R^2$) and the unit circle $C$ in $Bbb R^2$.
There's a nice map ("radial projection") from the first to the second defined as follows:
$$
f(x, y) = begin{cases}
(frac{x}{sqrt{y^2+1}}, frac{y}{sqrt{y^2 + 1}})& x = pm 1 \
(frac{x}{sqrt{x^2+1}}, frac{y}{sqrt{x^2 + 1}})& y = pm 1 \
end{cases}
$$
which cane be written, more generally, as $f(x, y) = frac{1}{sqrt{x^2 + y^2}} (x, y)$, but I wanted to emphasize that it's defined on the square, and that at the four corners, the expressions involved shift from a dependence on $x$ to a dependence on $y$ or vice versa.
The inverse of $f$ is
$$
g(x, y) = begin{cases}
(frac{x}{|x|}, frac{y}{|x|}) & |x| ge |y|\
(frac{x}{|y|}, frac{y}{|y|}) & |x| le |y|
end{cases}
$$
Now one smoothness structure on $S$ can be described as follows: we say that a function
$$
u: S to Bbb R
$$ is smooth if and only iff
$$
u circ g : C to Bbb R
$$
is smooth.
With this definition, the square $S$ is a smooth manifold, and it's diffeomorphic to the circle $C$, with $g$ being the diffeomorphism.
There's a small caveat here, though: the inclusion map
$$
i : S to Bbb R^2: (x, y) mapsto (x, y)
$$
that embeds the square in the plane is not a smooth embedding.
What about higher dimensions? Well, an exact analog to $f$ can be written using more variables (and the "general" formula that I gave after the "cases" formula); the analog of $g$ involves 3 cases for a cube in 3-space (look at $|x|, |y|, |z|$: each case handles the situations where one of these is the largest).
When we get to 4-space, it's the same deal, but with another variable, and the formula for $g$ has four cases.
But everything else I said (including the fact that with the resulting smoothness structure, the standard embedding of the square/cube/hypercube is not a smooth embedding) remains true.
what's $s$ in $scirc g$?
– Lau
Dec 5 '18 at 3:16
Fixed. It's "u" -- just a typo. Sorry about that.
– John Hughes
Dec 5 '18 at 12:44
I think I have got your point, thanks a lot.
– Lau
Dec 5 '18 at 12:47
add a comment |
Let me answer this in lower dimensions:
First, consider the bi-unit square $S$ (the boundary of $[-1, 1] times [-1, 1]$ in $Bbb R^2$) and the unit circle $C$ in $Bbb R^2$.
There's a nice map ("radial projection") from the first to the second defined as follows:
$$
f(x, y) = begin{cases}
(frac{x}{sqrt{y^2+1}}, frac{y}{sqrt{y^2 + 1}})& x = pm 1 \
(frac{x}{sqrt{x^2+1}}, frac{y}{sqrt{x^2 + 1}})& y = pm 1 \
end{cases}
$$
which cane be written, more generally, as $f(x, y) = frac{1}{sqrt{x^2 + y^2}} (x, y)$, but I wanted to emphasize that it's defined on the square, and that at the four corners, the expressions involved shift from a dependence on $x$ to a dependence on $y$ or vice versa.
The inverse of $f$ is
$$
g(x, y) = begin{cases}
(frac{x}{|x|}, frac{y}{|x|}) & |x| ge |y|\
(frac{x}{|y|}, frac{y}{|y|}) & |x| le |y|
end{cases}
$$
Now one smoothness structure on $S$ can be described as follows: we say that a function
$$
u: S to Bbb R
$$ is smooth if and only iff
$$
u circ g : C to Bbb R
$$
is smooth.
With this definition, the square $S$ is a smooth manifold, and it's diffeomorphic to the circle $C$, with $g$ being the diffeomorphism.
There's a small caveat here, though: the inclusion map
$$
i : S to Bbb R^2: (x, y) mapsto (x, y)
$$
that embeds the square in the plane is not a smooth embedding.
What about higher dimensions? Well, an exact analog to $f$ can be written using more variables (and the "general" formula that I gave after the "cases" formula); the analog of $g$ involves 3 cases for a cube in 3-space (look at $|x|, |y|, |z|$: each case handles the situations where one of these is the largest).
When we get to 4-space, it's the same deal, but with another variable, and the formula for $g$ has four cases.
But everything else I said (including the fact that with the resulting smoothness structure, the standard embedding of the square/cube/hypercube is not a smooth embedding) remains true.
Let me answer this in lower dimensions:
First, consider the bi-unit square $S$ (the boundary of $[-1, 1] times [-1, 1]$ in $Bbb R^2$) and the unit circle $C$ in $Bbb R^2$.
There's a nice map ("radial projection") from the first to the second defined as follows:
$$
f(x, y) = begin{cases}
(frac{x}{sqrt{y^2+1}}, frac{y}{sqrt{y^2 + 1}})& x = pm 1 \
(frac{x}{sqrt{x^2+1}}, frac{y}{sqrt{x^2 + 1}})& y = pm 1 \
end{cases}
$$
which cane be written, more generally, as $f(x, y) = frac{1}{sqrt{x^2 + y^2}} (x, y)$, but I wanted to emphasize that it's defined on the square, and that at the four corners, the expressions involved shift from a dependence on $x$ to a dependence on $y$ or vice versa.
The inverse of $f$ is
$$
g(x, y) = begin{cases}
(frac{x}{|x|}, frac{y}{|x|}) & |x| ge |y|\
(frac{x}{|y|}, frac{y}{|y|}) & |x| le |y|
end{cases}
$$
Now one smoothness structure on $S$ can be described as follows: we say that a function
$$
u: S to Bbb R
$$ is smooth if and only iff
$$
u circ g : C to Bbb R
$$
is smooth.
With this definition, the square $S$ is a smooth manifold, and it's diffeomorphic to the circle $C$, with $g$ being the diffeomorphism.
There's a small caveat here, though: the inclusion map
$$
i : S to Bbb R^2: (x, y) mapsto (x, y)
$$
that embeds the square in the plane is not a smooth embedding.
What about higher dimensions? Well, an exact analog to $f$ can be written using more variables (and the "general" formula that I gave after the "cases" formula); the analog of $g$ involves 3 cases for a cube in 3-space (look at $|x|, |y|, |z|$: each case handles the situations where one of these is the largest).
When we get to 4-space, it's the same deal, but with another variable, and the formula for $g$ has four cases.
But everything else I said (including the fact that with the resulting smoothness structure, the standard embedding of the square/cube/hypercube is not a smooth embedding) remains true.
edited Dec 5 '18 at 12:44
answered Dec 4 '18 at 14:43
John Hughes
62.4k24090
62.4k24090
what's $s$ in $scirc g$?
– Lau
Dec 5 '18 at 3:16
Fixed. It's "u" -- just a typo. Sorry about that.
– John Hughes
Dec 5 '18 at 12:44
I think I have got your point, thanks a lot.
– Lau
Dec 5 '18 at 12:47
add a comment |
what's $s$ in $scirc g$?
– Lau
Dec 5 '18 at 3:16
Fixed. It's "u" -- just a typo. Sorry about that.
– John Hughes
Dec 5 '18 at 12:44
I think I have got your point, thanks a lot.
– Lau
Dec 5 '18 at 12:47
what's $s$ in $scirc g$?
– Lau
Dec 5 '18 at 3:16
what's $s$ in $scirc g$?
– Lau
Dec 5 '18 at 3:16
Fixed. It's "u" -- just a typo. Sorry about that.
– John Hughes
Dec 5 '18 at 12:44
Fixed. It's "u" -- just a typo. Sorry about that.
– John Hughes
Dec 5 '18 at 12:44
I think I have got your point, thanks a lot.
– Lau
Dec 5 '18 at 12:47
I think I have got your point, thanks a lot.
– Lau
Dec 5 '18 at 12:47
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3022708%2fcan-the-surface-of-a-3-dimension-cube-be-diffeomorphic-to-a-3-dimension-sphere%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Do you mean the surface of the unit hypercube in $Bbb R^4$, with the differential structure inherited from $Bbb R^4$? I don't really know what happens at the edges and vertices there, but it looks messy.
– Arthur
Dec 2 '18 at 14:51
Can you define what you mean by "3-dimensional cube" and by "3-dimensional sphere"? I would think that the former is the three-fold product of the unit interval, and the latter is the unit sphere in $Bbb R^4$. But those two spaces are not homeomorphic (e.g. their homology distinguishes them).
– Danu
Dec 2 '18 at 15:34
I think you mean a $3$ dimensional ball, which is a solid object like the earth. We use sphere to represent the surface of a ball.
– Ross Millikan
Dec 2 '18 at 16:07
In addition, in order to ask if two things are diffeomorphic, both things must be smooth manifolds. So, you must first choose some kind of atlas on the cube.
– Jason DeVito
Dec 4 '18 at 14:24
So the question is, if there exist a kind of atlas on cube, such that the cube with the atlas can be a smooth manifolds.
– Lau
Dec 4 '18 at 14:26