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Gravity is a dimension?

  1. Jan 4, 2009 #1
    Hey everyone. I was recently on youtube, looking at 4-d objects, when I came across a comment which caught my eye:

    "You're forgetting Gravity. Without gravity there is no xyz and without two large bodies there is no concept of time. Therefore, gravity must be included as a dimension. They are known as XYZTG, and basic physics explains. However, quantum physics predicts that there my be more than that, probably even 11. I won't go into all of them but given enough time I guess I could do a few if you really want me to."

    Ignoring any technical mistakes that he might have in his understanding, I'm curious if the underlying idea is correct. Is gravity a dimension?

    Thank you.

    edit: This post possibly belongs in the string theory forum. If that's the case, sorry.
  2. jcsd
  3. Jan 4, 2009 #2


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    This makes no sense.

    Look in QM. Write down the Hamiltonian for, say, an EM interaction. Where's gravity there? There isn't. Yet, I have no only space, but time incorporated in the Hamiltonian. Isn't this rather obvious and falsify what you read?

    Now, whether gravity can "leak" into other higher dimension is a different matter, but that has nothing to do with gravity being a "dimension".

    BTW, it is already difficult enough for us to tackle question based on valid sources. It is going to be ridiculous to entertain stuff you heard off YouTube and without giving us the exact source. We have no way to verify that you heard this right, or if the source is crackpottery. If you haven't been told already or haven't read my many comments on this, please provide the exact reference to the source that you wish to ask on. Without it, this whole thing can easily be a waste of time.

  4. Jan 4, 2009 #3
    Yea, that does seem kind of obvious now. I realize it's not a valid source, but it's something I read which got me thinking and after some thought, it seemed... plausible(?).
    I copy and pasted what was said in full. I didn't know where to look to validate his thought, so I turned to you guys.
    Thanks for the reply.
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