# If we can move at the speed of light, can we pass a small hole?

1. Mar 11, 2015

### beste ulusoy

If we can motion at speed of light,can we pass a small hole like a keyhole? Of course in suitable conditions...

2. Mar 11, 2015

### Chronos

The speed of light is only achievable by massless particles. It would be fascinating to see what a massless particle sees, but, we haven't figured out how to mount a massless camera on one to observe what happens.

3. Mar 11, 2015

### Essence

So you probably know that moving at the speed of light is not considered possible (for something with mass). This is related to the fact that as you get faster your mass increases, which makes it harder to go even faster (requires more energy) until it will actually require an infinite amount of energy to increase your speed even more.

However, let's pretend we are really close to the speed of light. In this case there is something called length contraction which will make an object very skinny in the direction that it is moving when observed by someone who is watching it pass by at that really fast speed (close to the speed of light). The object will get skinnier but it will not get shorter (or less wide) so it will not fit through through the key hole. By the way in this case

---------> If this is the direction the object is moving in
-------------> this is the dimension of the object that is "skinny"

if an object looked like this (and was moving right very fast) :
--------------------
--------------------
--------------------

it could start to look like this (at high enough speeds):

------
------
------

I should tell you that I have not taken unusually advanced physics yet. It is possible outside of normal special relativity that there is a theory somewhere that suggests otherwise, but I am 99% confident in my answer.

4. Mar 12, 2015

### beste ulusoy

i just ask my question out of all rules.this is just a think.if we can move at speed of light(assume),can we pass a little hole
for example how to fit these huge stars to our eyes,how can we see them

5. Mar 12, 2015

### Staff: Mentor

I cannot understand you. Are you asking how we can see stars?
Are you asking if we can fit large objects through small holes while traveling at near-light speed?

6. Mar 12, 2015

### phinds

It is unacceptable to assume we can move at the speed of light.

Your question is like asking "if the laws of physics do not apply, what do the laws of physics say about <insert nonsense of your choice>"

7. Mar 12, 2015

### ZapperZ

Staff Emeritus
This is a typical "When did you stop beating your wife?" question.

Secondly, even with applying length contraction, the contraction is only along the direction of motion, not in the transverse direction! Your transverse size is still the SAME!

Zz.

8. Mar 12, 2015

### Orodruin

Staff Emeritus
The truth of this sentence is conditioned on "mass" meaning "relativistic mass", a concept most physicists tend to avoid. For the reasons why, see our FAQ on the subject: https://www.physicsforums.com/threads/what-is-relativistic-mass-and-why-it-is-not-used-much.796527/ [Broken]

Last edited by a moderator: May 7, 2017
9. Mar 12, 2015

### DaveC426913

I'm still trying to figure out what he means by "can we pass a small hole like a keyhole".

10. Mar 12, 2015

### phinds

I think he's totally confused about length contraction and thinks that things set skinnier along their line of travel and if they get skinny enough they could pass through a keyhole.

11. Mar 12, 2015

### A.T.

You can pass almost everything if you move fast enough... and don't care about surviving it.

12. Mar 12, 2015

### Staff: Mentor

Perhaps we should wait and see what the OP says instead of trying to guess.

13. Mar 12, 2015

### DaveC426913

Ohhhh. Pass through the keyhole.
Because of length contraction.

OK, I get what he's asking now.

14. Mar 12, 2015

### phinds

Yeah, but guessing is so much more fun ... and apparently none of us have anything better to do anyway

15. Mar 12, 2015

### bahamagreen

"pass a small hole like a keyhole"

I think this means pass through a slot... the OP may be confused about the dimension of contraction, unless he is thinking of something like this:

The object's path has two components, vertical Y and horizontal X, so the observed contraction may be in the X dimension, but that contraction allows the object to slip in the Y direction though a slot with its long axis oriented in the Z dimension, so as to accept passage of the X contracted object "sideways" ...

Kind of like throwing a loaf of bread fast enough that it contracts to the thickness of a single slice, and then that slice takes on a vertical component to fall into the slot of an awaiting toaster oriented sideways...

But yeah, let's see if the OP can clarify...

16. Mar 12, 2015

### phinds

I think the OP's a drive-by and we're just flailing around

17. Mar 12, 2015

### DaveC426913

It's only been 18 hours...

18. Mar 12, 2015

### phinds

Yeah, but patience is not one of my virtues

19. Mar 12, 2015

### OCR

Well, you could edit your typo... ...

20. Mar 12, 2015

### phinds

an innocent slip of the figner

21. Mar 12, 2015

### OCR

Understood...

22. Mar 13, 2015

### jimgraber

Just for fun, let's try to put a photon, an electron and a proton through that small hole.

The photon does not get any faster, but as it gets more energetic, it gets “skinnier” sideways (transversely) as well as longitudinally.

If I understand what I have read correctly, the electron-electron collision cross section also shrinks with increasing energy.

The proton-proton collision cross section, on the other hand increases with increasing energy.

(For nice pictures, google electron electron cross section images and also proton proton cross section images.)

Thanks.

Jim Graber

23. Mar 13, 2015

### beste ulusoy

do you understand me? and do you agree with me partially?

Last edited by a moderator: Mar 13, 2015
24. Mar 13, 2015

### beste ulusoy

what's the reason of a big object can not go through in a small hole? i guess, it is the distance between them and the elapsed time. because when the object is far away, it is as small as can go through in a small hole. but as long as the object approach the hole, namely, as long as it passes the road and the time, the possibility of the object's ability to go through in the hole gets low. if this object moves as fast as speed of light the distance between the hole and the object disappears instantly. so can the object go through in the hole?

25. Mar 13, 2015

### Staff: Mentor

This is a truly bizarre comment. Do you actually believe that a star can go through a hole the size of your pupil because it is far away and therefore small enough? I must be really misunderstanding you, because this is the type of geometrical idea that even a very young child knows is wrong.

No.